Potassium level
Potassium is the major cation inside cells. Two US survey laboratory manuals print adult ranges of 3.3 to 5.1 and 3.5 to 5.0 mEq/L, and guideline bodies start grading high potassium at 5.0 or 5.5. In 1.2 million people, deaths were lowest at 4 to 4.5 and rose on both sides. Hemolysis and fist clenching can raise a result falsely.
- Status
- Part of routine basic and comprehensive metabolic blood panels, ordered by a clinician and also sold direct to consumers by some US laboratories. FDA classifies potassium test systems as class II devices [1]. Reports print the unit as mEq/L or mmol/L, and for potassium the two give the same number.
- Measures
- The concentration of potassium in serum or plasma. Potassium is the major positively charged ion inside cells and is critical to nerve and muscle cell activity [2].
- Also called
- potassium, serum potassium, potassium serum, plasma potassium, K, K+, potassium blood test, kalemia
- Tested for
- electrolyte balance, heart rhythm, muscle cramps, muscle weakness, kidney function, blood pressure medication monitoring, diuretic monitoring, checking a potassium supplement
Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on
Linked in research3
- ModerateLinked to more deaths at both low and high potassium, with the lowest risk at 4 to 4.5 mEq/L across 1.2 million people.
- ModerateLinked to more rhythm problems at low potassium and more cardiovascular deaths at high potassium in a meta-analysis of 24 observational studies.
- LimitedOne trial found raising potassium to 4.5 to 5.0 mEq/L cut a combined count of arrhythmia events, hospital stays and deaths by 24% in people with implanted defibrillators.
Reported risks0
No risks sourced yet.
Reference ranges
Each range is the one its source published, in mEq/L. Also reported in mmol/L. Where sources differ, each is shown.
US national survey laboratory procedure manual, 2017 to 2018
Adults, as the reference range printed for the serum assay · [2], [3]
| Range | What the source calls it |
|---|---|
| below 3.3 mEq/L | No name given |
| 3.3 to 5.1 mEq/L | "reference range" |
| above 5.1 mEq/L | No name given |
The reference range listed in the laboratory manual for the method used in the 2017 to 2018 US National Health and Nutrition Examination Survey (Roche Cobas 6000, indirect ion-selective electrode, serum). It is the range attached to that assay, not one derived from survey participants [2]. The manual prints the range in mmol/L. For potassium that is the same number as mEq/L: the 2015 to 2016 manual labels the survey's potassium variable in mmol/L and prints its reference range in mEq/L [3].
US national survey laboratory procedure manual, 2015 to 2016
People older than 10, as the reference range printed for the assay · [3]
| Range | What the source calls it |
|---|---|
| below 3.5 mEq/L | No name given |
| 3.5 to 5 mEq/L | "reference range" |
| above 5 mEq/L | No name given |
From the manual for the method used in the 2015 to 2016 survey (Beckman UniCel DxC 800, run by Collaborative Laboratory Services). The manual states that its reference ranges were established from wellness participants with an age mix similar to the laboratory's patients. Two assays used by the same national survey print different ranges [3][2].
US national survey laboratory procedure manual, 2015 to 2016, children aged 5 to 10
Children aged 5 to 10 · [3]
| Range | What the source calls it |
|---|---|
| below 3.4 mEq/L | No name given |
| 3.4 to 5.4 mEq/L | "reference range" |
| above 5.4 mEq/L | No name given |
The manual attributes its pediatric ranges to a 1995 multicenter guideline for the analyzer, built on data from Montreal, Miami and Denver. The manual prints the age bands as 5 to 10 and older than 10 without saying which band a child of exactly 10 falls in [3].
US national survey laboratory procedure manual, 2015 to 2016, children aged 1 to 5
Children aged 1 to 5 · [3]
| Range | What the source calls it |
|---|---|
| below 3.2 mEq/L | No name given |
| 3.2 to 5.7 mEq/L | "reference range" |
| above 5.7 mEq/L | No name given |
From the same manual and the same 1995 pediatric guideline for the analyzer [3].
US national survey laboratory procedure manual, 2015 to 2016, infants aged 1 month to 1 year
Infants aged 1 month to 1 year · [3]
| Range | What the source calls it |
|---|---|
| below 3.6 mEq/L | No name given |
| 3.6 to 6.8 mEq/L | "reference range" |
| above 6.8 mEq/L | No name given |
From the same manual and the same 1995 pediatric guideline for the analyzer. The upper limit for infants is above the level that guideline bodies grade as severe in adults [3][4].
US national survey laboratory procedure manual, 2015 to 2016, newborns under 1 month
Newborns from birth to 1 month · [3]
| Range | What the source calls it |
|---|---|
| below 3.9 mEq/L | No name given |
| 3.9 to 6.9 mEq/L | "reference range" |
| above 6.9 mEq/L | No name given |
From the same manual and the same 1995 pediatric guideline for the analyzer [3].
European Resuscitation Council guidelines, 2021
People with low or high potassium, graded by concentration · [5]
| Range | What the source calls it |
|---|---|
| below 2.5 mEq/L | "severe hypokalemia" A doctor, immediately |
| 2.5 to 2.9 mEq/L | "moderate hypokalemia" |
| 3 to 3.4 mEq/L | "mild hypokalemia" |
| 3.5 to 5.4 mEq/L | No name given |
| 5.5 to 5.9 mEq/L | "mild hyperkalemia" |
| 6 to 6.4 mEq/L | "moderate hyperkalemia" |
| 6.5 or above mEq/L | "severe hyperkalemia" A doctor, immediately |
From the Council's guideline on cardiac arrest in special circumstances. It defines hypokalemia as a serum potassium below 3.5 mmol/L, and counts a result as severe when it is below 2.5 mmol/L or when symptoms are present. For high potassium it states that there is no universal definition and that hyperkalemia is a continuum in practice. It reports that 15% of patients with potassium of 6.5 mmol/L or above had an arrhythmia or cardiac arrest within 6 hours of an electrocardiogram and before treatment began. The bands were read in the Council's official German-language edition, which prints them as leicht, mittel and schwer for low potassium and mild, moderat and schwer for high potassium. The English labels here are translations of those words [5].
UK Kidney Association clinical practice guideline, 2026 update
Adults with high potassium, graded by concentration · [4]
| Range | What the source calls it |
|---|---|
| below 5.5 mEq/L | No name given |
| 5.5 to 5.9 mEq/L | "mild" |
| 6 to 6.4 mEq/L | "moderate" |
| 6.5 or above mEq/L | "severe" A doctor, immediately |
The guideline states that there is no universally accepted definition of hyperkalemia and that it adopted the European Resuscitation Council threshold of 5.5 mmol/L. It covers high potassium only, so this block does not classify low results. It describes severe hyperkalemia as potentially life-threatening [4].
Kidney Disease: Improving Global Outcomes conference report, 2020
People with acute high potassium and no electrocardiogram changes · [6]
| Range | What the source calls it |
|---|---|
| below 5 mEq/L | No name given |
| 5 to 5.9 mEq/L | "mild" |
| 6 to 6.4 mEq/L | "moderate" |
| 6.5 or above mEq/L | "severe" A doctor, immediately |
An expert opinion classification from a controversies conference, not a graded guideline. It starts at 5.0 mmol/L or the laboratory's upper limit of normal, half a unit below the threshold used by the two bodies above. It moves each result up one grade when electrocardiogram changes are present: 5.0 to 5.9 becomes moderate and 6.0 or above becomes severe. It covers high potassium only, so this block does not classify low results [6].
Šupak-Smolčić and colleagues, Croatian pregnancy cohort, 2025, first trimester
Pregnant women at 11 to 14 weeks of gestation · [7]
| Range | What the source calls it |
|---|---|
| below 3.7 mEq/L | No name given |
| 3.7 to 4.8 mEq/L | "reference interval" |
| above 4.8 mEq/L | No name given |
The central 95% of results in 299 women with singleton pregnancies at one Croatian center, measured in serum by indirect ion-selective electrode on a Roche Cobas 6000. The authors compare it with the 3.9 to 5.1 mmol/L range that Croatian laboratories use for non-pregnant women and found no clinically significant change in potassium in early pregnancy. The study covers the first trimester only [7].
What has been shown to move it
Shown to lower it4
Low blood potassium
Shown to lower blood potassium by about 0.36 mmol/L after a single dose. The label calls the drop usually temporary.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- A single dose of a beta-agonist lowered potassium by 0.36 mmol/L (95% CI 0.18 to 0.54) against placebo [12]. The label states beta-agonists may produce significant hypokalemia in some patients, usually transient and not needing supplements [1].
- Population
- Single-dose trials in people with asthma or COPD [12].
- Sources
- [12], [1]
- Caveats
- An average change, not a rate of clinically low potassium.
Low potassium
Shown to lower blood potassium, with low potassium in 6.0% on chlorthalidone and 4.4% on hydrochlorothiazide in a head-to-head trial.
Across placebo-controlled trials, thiazides lowered potassium in a dose-related way, least with hydrochlorothiazide.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- In the head-to-head trial, hypokalemia occurred in 6.0% on chlorthalidone and 4.4% on hydrochlorothiazide [7]. In a cohort of first-time users, hypokalemia was more frequent on chlorthalidone (HR 2.72, 95% CI 2.38 to 3.12) [8]. Across placebo-controlled trials, thiazides lowered potassium in a dose-related way, least with hydrochlorothiazide [1]. Hypokalemia was more frequent than on placebo in the kidney stone and kidney disease trials [13][3]. The hydrochlorothiazide label states that hypokalemia may cause cardiac arrhythmia and may heighten the heart's response to the toxic effects of digitalis [14].
- Population
- 13,523 adults aged 65 and older [7]; 730,225 first-time users [8]; 11,282 people in 60 trials [1].
- Sources
- [7], [8], [1], [13], [3], [14]
- Caveats
- The two rates compare the drugs with each other. None of these abstracts gives a placebo rate.
Lowering high blood potassium
Small studies found inhaled and nebulized beta-agonists lowered blood potassium in hyperkalemia, and adding insulin with glucose lowered it more than either alone.
Compared with control groups in small trials, which the abstract does not describe [9]
The numbers and sources
- Effect
- Inhaled and nebulized beta-agonists and intravenous insulin with glucose all lowered serum potassium, and nebulized beta-agonists combined with insulin and glucose lowered it more than either alone. No study reported deaths or heart rhythm problems [9].
- Population
- Small randomized studies of emergency treatments for hyperkalemia [9].
- Sources
- [9]
- Caveats
- Many studies were small, and the abstract gives no effect sizes. This is a hospital use, not one on the inhaler label [9].
Low potassium
Linked to low potassium, more at higher doses, in 14.7% of bumetanide patients tested, while low torsemide doses for blood pressure did not raise it above placebo.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- Low potassium was reported in 14.7% of patients tested on bumetanide [15]. On torsemide 5 or 10 mg for hypertension, serum potassium fell a mean 0.1 mEq/L over 6 weeks, and 1.5% on torsemide and 3% on placebo dropped below 3.5 mEq/L. At the higher doses used for heart failure, cirrhosis or kidney disease, low potassium was more frequent and dose related [1]. In kidney injury trials, diuretics made little or no difference to low potassium (RR 1.20 for prevention, 1.52 for treatment) [12].
- Population
- Bumetanide-treated patients [15]; 564 people on torsemide and 274 on placebo in US trials [1]; 1,383 and 478 people in kidney injury trials [12].
- Sources
- [15], [1], [12]
- Caveats
- The bumetanide figure has no placebo group. Rates depend heavily on dose and on other drugs taken.
Shown to raise it11
High blood potassium
Shown to raise blood potassium, above 5.7 mEq/L in 2.2% of people treated for high blood pressure and 4.8% treated for heart failure.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- In clinical trials of lisinopril, serum potassium above 5.7 mEq/L occurred in 2.2% of people with hypertension and 4.8% of people with heart failure. In ATLAS, hyperkalemia was reported in 6% on the high dose and 4% on the low dose. The label lists kidney impairment, diabetes, potassium-sparing diuretics, potassium supplements and potassium salt substitutes as risk factors [3].
- Population
- People in lisinopril clinical trials, including 3,164 in ATLAS [3].
- Sources
- [3]
- Caveats
- The label gives no placebo rate for these figures.
With an ARB or aliskiren
Shown to raise high potassium, low blood pressure and kidney failure when an ACE inhibitor is combined with an ARB or aliskiren, with no fewer deaths.
The numbers and sources
- How common
- Very common: more than 1 in 10 people.
- Effect
- Across 33 trials, combining two blockers of the renin-angiotensin system did not lower all-cause mortality against one (RR 0.97, 95% CI 0.89 to 1.06) and raised hyperkalemia by 55%, low blood pressure by 66% and kidney failure by 41% [26]. In ONTARGET, ramipril plus telmisartan brought more low blood pressure symptoms (4.8% against 1.7%), fainting (0.3% against 0.2%) and kidney dysfunction (13.5% against 10.2%) than ramipril alone, with no difference in cardiovascular events (16.3% against 16.5%) [15]. In people with diabetic kidney disease, lisinopril added to losartan raised hyperkalemia (6.3 against 2.6 events per 100 person-years) and acute kidney injury (12.2 against 6.7), and the trial was stopped early [27].
- Population
- 68,405 people in 33 trials, mean 52 weeks [26]; 17,078 people assigned to the combination or ramipril alone [15]; 1,448 people with type 2 diabetes and kidney disease [27].
- Sources
- [26], [15], [27]
- Caveats
- Hospital admissions for heart failure fell 18% on dual therapy in the pooled analysis [26]. The lisinopril label describes the same findings [3].
High blood potassium
Shown to raise blood potassium, reported as hyperkalemia in 2% on valsartan against 1% on placebo in heart failure trials.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- In heart failure trials, hyperkalemia was reported in 2% on valsartan and 1% on placebo, and 0.5% against 0.1% stopped treatment over raised potassium [14]. The losartan label lists hyperkalemia among the events more frequent than placebo in its diabetic kidney disease trial, and warns that other drugs that raise potassium may lead to hyperkalemia [10].
- Population
- 3,282 people on valsartan and 2,740 on placebo in heart failure trials [14]; 1,513 people in the losartan kidney trial [10].
- Sources
- [14], [10]
- Caveats
- About 93% of people in the valsartan heart failure trials also took an ACE inhibitor [14].
With an ACE inhibitor or aliskiren
Shown to raise high potassium, low blood pressure and kidney failure when an ARB is combined with an ACE inhibitor or aliskiren, with no fewer deaths.
The numbers and sources
- How common
- Very common: more than 1 in 10 people.
- Effect
- Across 33 trials, combining two blockers of the renin-angiotensin system did not lower all-cause mortality against one (RR 0.97, 95% CI 0.89 to 1.06) and raised hyperkalemia by 55%, low blood pressure by 66% and kidney failure by 41% [36]. In ONTARGET, telmisartan plus ramipril brought more low blood pressure symptoms (4.8% against 1.7%) and kidney dysfunction (13.5% against 10.2%) than ramipril alone [16]. In people with diabetic kidney disease on losartan, adding lisinopril raised hyperkalemia (6.3 against 2.6 events per 100 person-years) and acute kidney injury (12.2 against 6.7), and the trial was stopped early [37].
- Population
- 68,405 people in 33 trials, mean 52 weeks [36]; 17,078 people assigned to the combination or ramipril alone [16]; 1,448 people with type 2 diabetes and kidney disease [37].
- Sources
- [36], [16], [37]
- Caveats
- Hospital admissions for heart failure fell 18% on dual therapy in the pooled analysis [36]. The losartan label carries the same warning [10].
Raised blood potassium and hyperkalemia
Salt substitutes raised blood potassium slightly, and hyperkalemia was about as common as on regular salt. Trials excluded people at known risk.
Increased potassium intake had no adverse effect on kidney function in adults.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- Salt substitutes raised blood potassium by 0.12 mmol/L (95% CI 0.07 to 0.18) and made little to no difference in hyperkalemia (4 more per 100,000, 95% CI 47 fewer to 121 more) [3]. In the stroke trial, serious adverse events attributed to hyperkalemia were 3.35 against 3.30 per 1,000 person-years (rate ratio 1.04, 95% CI 0.80 to 1.37) [6]. Increased potassium intake had no adverse effect on kidney function in adults [1]. In POTCAST, hospitalization for high or low potassium was similar between groups [8]. Hyperkalemia occurred in 3% of those on potassium supplements alone and 0.2% of controls [10].
- Population
- 784 adults in 6 RCTs for blood potassium, 22,849 in 5 RCTs for hyperkalemia [3]; 20,995 people [6]; 1,200 adults with a defibrillator [8][10].
- Sources
- [1], [3], [6], [8], [10]
- Caveats
- All 26 trials in the Cochrane review excluded people in whom extra potassium is known to be harmful. The reviewers found no evidence in those people, or in pregnant women [3].
Higher blood potassium with salt substitutes
Shown to raise blood potassium slightly, by 0.12 mmol/L, in trials that excluded people at risk. Serious high potassium events did not differ from regular salt.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Low-sodium salt substitutes raised blood potassium by 0.12 mmol/L (95% CI 0.07 to 0.18, 6 trials) and made little or no difference to hyperkalemia (4 more per 100,000, 95% CI 47 fewer to 121 more, 5 trials) [7]. In the large trial, serious adverse events attributed to hyperkalemia occurred at 3.35 against 3.30 per 1,000 person-years (rate ratio 1.04, 95% CI 0.80 to 1.37) [10]. A network meta-analysis found no substitute increased adverse events or withdrawals [8].
- Population
- 784 adults for blood potassium and 22,849 for hyperkalemia [7]. 20,995 older Chinese adults [10]. 34 trials [8].
- Sources
- [7], [10], [8]
- Caveats
- Every trial excluded people for whom more potassium is known to be harmful, so these results do not cover them [7]. The network meta-analysis authors limit their safety conclusion to people without kidney impairment [8].
High blood potassium
Shown to about double high blood potassium in heart failure, 18.7% against 9.1% on placebo in one trial. Rates in healthy young women matched baseline.
In resistant hypertension, potassium exceeded 6.0 mmol/L once in 6 of 285 people.
The numbers and sources
- How common
- Very common: more than 1 in 10 people.
- Effect
- In heart failure with preserved ejection fraction, hyperkalemia occurred in 18.7% on spironolactone and 9.1% on placebo [4]. Across four trials of this drug class, the odds of hyperkalemia doubled (OR 2.27, 95% CI 2.02 to 2.56), and serious hyperkalemia above 6.0 mmol/L occurred in 2.9% against 1.4% [2]. In resistant hypertension, potassium exceeded 6.0 mmol/L once in 6 of 285 people [5]. After RALES was published, hospitalization for hyperkalemia among older Ontario heart failure patients on ACE inhibitors rose from 2.4 to 11.0 per 1,000, and the associated deaths from 0.3 to 2.0 per 1,000 [16]. Among healthy young women taking spironolactone for acne, 0.72% of potassium measurements were high, against 0.76% at baseline in that population [17].
- Population
- 3,445 people with heart failure [4]; 13,846 people in four heart failure trials [2]; 285 people with resistant hypertension [5]; more than 1.3 million Ontario adults aged 66 or older [16]; 974 healthy young women with 1,802 potassium measurements [17].
- Sources
- [4], [2], [5], [16], [17]
- Caveats
- The risk depends on who is taking it. The label names impaired kidney function, potassium supplements and drugs that raise potassium as factors [3]. Low potassium was halved on these drugs in heart failure (7% against 14%) [2].
With trimethoprim-sulfamethoxazole
Linked to hospital admission for high potassium and to sudden death in adults over 65 on an ACE inhibitor or ARB given this antibiotic.
The numbers and sources
- How common
- Uncommon: between 1 in 1,000 and 1 in 100 people.
- Effect
- Among older adults on an ACE inhibitor or ARB, hospital admission with hyperkalemia within 14 days was about 7 times as likely after trimethoprim-sulfamethoxazole as after amoxicillin (adjusted OR 6.7, 95% CI 4.5 to 10.0). Other antibiotics studied showed no such rise [29]. Sudden death within 7 days was also more likely than after amoxicillin (adjusted OR 1.38, 95% CI 1.09 to 1.76), about 3 sudden deaths within 14 days per 1,000 prescriptions [30].
- Population
- Ontario residents aged 66 or older on an ACE inhibitor or ARB, with 4,148 hyperkalemia admissions over 14 years [29] and 39,879 sudden deaths from 1994 to 2012 [30].
- Sources
- [29], [30]
- Caveats
- Observational studies in older adults from one province. Ciprofloxacin was also associated with sudden death in the second study [30].
With trimethoprim-sulfamethoxazole
Linked to hospital admission for high potassium and to sudden death in adults over 65 on an ARB or ACE inhibitor given this antibiotic.
The numbers and sources
- How common
- Uncommon: between 1 in 1,000 and 1 in 100 people.
- Effect
- Among older adults on an ARB or ACE inhibitor, hospital admission with hyperkalemia within 14 days was about 7 times as likely after trimethoprim-sulfamethoxazole as after amoxicillin (adjusted OR 6.7, 95% CI 4.5 to 10.0) [39]. Sudden death within 7 days was also more likely than after amoxicillin (adjusted OR 1.38, 95% CI 1.09 to 1.76), about 3 sudden deaths within 14 days per 1,000 prescriptions [40].
- Population
- Ontario residents aged 66 or older on an ACE inhibitor or ARB, with 4,148 hyperkalemia admissions over 14 years [39] and 39,879 sudden deaths from 1994 to 2012 [40].
- Sources
- [39], [40]
- Caveats
- Observational studies in older adults from one province. Neither abstract separates ARB users from ACE inhibitor users.
With ACE inhibitors or ARBs
Linked to more hospital stays for high potassium, rising from 2.4 to 11.0 per 1,000 older heart failure patients on ACE inhibitors as spironolactone use grew.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- Among older adults on ACE inhibitors recently hospitalized for heart failure, spironolactone prescriptions rose from 34 to 149 per 1,000 patients between 1994 and 2001. Over the same period hospitalization for hyperkalemia rose from 2.4 to 11.0 per 1,000 and the associated deaths from 0.3 to 2.0 per 1,000, an estimated 560 additional hospitalizations [16]. The label names ACE inhibitors and ARBs among drugs that raise the risk of hyperkalemia with spironolactone [3].
- Population
- More than 1.3 million Ontario adults aged 66 or older [16].
- Sources
- [16], [3]
- Caveats
- A population time-series, not a comparison of individuals. In RALES, where everyone took an ACE inhibitor, serious hyperkalemia was minimal in both groups [1].
With trimethoprim-sulfamethoxazole
Linked to hospital admission for high potassium, about 12 times as likely as after amoxicillin, and to sudden death in older adults on spironolactone.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Among older adults on long-term spironolactone, hospital admission for hyperkalemia within 14 days was far more likely after trimethoprim-sulfamethoxazole than after amoxicillin (adjusted OR 12.4, 95% CI 7.1 to 21.6) [20]. Sudden death within 14 days was also more likely (adjusted OR 2.46, 95% CI 1.55 to 3.90) [21].
- Population
- Ontario residents aged 66 or older on spironolactone, with 6,903 hyperkalemia admissions over 18 years [20] and 11,968 sudden deaths [21].
- Sources
- [20], [21]
- Caveats
- Observational, in older adults. The label lists trimethoprim among drugs that can raise potassium [3].
How it compares with the reference method
Did not match the reference method2
Falsely high results from hemolysis and the blood draw
Limited evidence: hemolysis and fist clenching raise the result falsely, and one UK clinic network saw results above range fall from 9% to 6% after changing how blood was drawn.
The numbers and sources
- Compared with
- The same blood without hemolysis, and results before the change in draw technique
- Effect
- Both survey manuals state that hemolysis falsely elevates potassium, and one instructs the laboratory not to use hemolyzed specimens [2][3]. In blood from 16 volunteers hemolyzed in the laboratory, clinically meaningful changes in potassium appeared at moderate hemolysis, with free hemoglobin above 1 g/L [12]. In UK primary care, after staff were trained not to ask patients to clench a fist, results at 5.2 mmol/L or higher fell from 9% to 6% of samples and results at 5.8 mmol/L or higher fell from 0.9% to 0.5% [13]. A kidney conference report lists fist clenching during the draw, mechanical trauma, tourniquet use for more than 1 minute, blood clotting and raised white cell or platelet counts as causes of a falsely elevated result [6]. A UK guideline names prolonged transit to the laboratory or poor storage as the most common cause, and also lists difficult venepuncture, a high platelet count, hemolysis and cold storage [4].
- Population
- 16 volunteers [12]. Primary care samples in one UK region from 2002 to 2005 [13].
- Sources
- [2], [3], [12], [13], [6], [4]
- Caveats
- The UK study compared periods before and after the change and was not randomized. Potassium in its samples was also inversely related to outdoor temperature [13]. The UK guideline states that recognizing a falsely high result matters because it avoids unnecessary treatment that could cause harm [4].
Serum against plasma
Limited evidence: serum reads 0.1 to 0.7 mEq/L higher than plasma, and up to 2.6 mEq/L higher in one study of people with blood cell disorders.
The numbers and sources
- Compared with
- Plasma potassium from the same person
- Effect
- A kidney conference report states that serum potassium is 0.1 to 0.7 mmol/L higher than plasma potassium and asks research reports to state which was measured [6]. In 435 patients with raised platelet, red cell or white cell counts and 30 controls, the difference between serum and plasma potassium was larger with raised platelets, raised red cells or both than in controls, was no different from controls with white cell disorders, and did not exceed 2.61 mmol/L [14]. A UK guideline defines pseudo-hyperkalemia as serum potassium more than 0.4 mmol/L above plasma potassium [4]. The conference report adds that point-of-care devices have limited accuracy and precision, with mean differences of 0.1 to 0.5 mmol/L from laboratory measurement for some devices [6].
- Population
- 435 patients with blood cell disorders and 30 controls [14].
- Sources
- [6], [14], [4]
- Caveats
- The patient study selected people with blood disorders, so its largest differences do not describe the general population [14]. Whether a result is serum or plasma potassium depends on the blood tube used, a clotted tube for serum or a lithium heparin tube for plasma [4].
What studies tie it to
Linked in research3
Death from any cause
Linked to more deaths at both low and high potassium, with the lowest risk at 4 to 4.5 mEq/L across 1.2 million people.
The numbers and sources
- Effect
- In an individual-level meta-analysis of 27 cohorts, the relation between potassium and death was U-shaped, with the lowest risk at 4 to 4.5 mmol/L. Against 4.2 mmol/L, the adjusted hazard ratio for death from any cause was 1.22 (95% CI 1.15 to 1.29) at 5.5 mmol/L and 1.49 (1.26 to 1.76) at 3.0 mmol/L. Risks were similar across levels of kidney function [8]. In two US community cohorts, potassium of 5.0 mEq/L or above went with more deaths from any cause than 4.0 to 4.4 mEq/L (HR 1.41, 95% CI 1.12 to 1.76), and the association was stronger in people using diuretics [9].
- Population
- 1,217,986 participants in 10 general population, 7 high cardiovascular risk and 10 chronic kidney disease cohorts, followed for a mean of 6.9 years [8]. 9,651 adults free of cardiovascular disease in the Multi-Ethnic Study of Atherosclerosis and the Cardiovascular Health Study [9].
- Sources
- [8], [9]
- Caveats
- Observational, from potassium measured in outpatients at baseline. The authors of the US cohort study write that whether keeping potassium within the normal range improves outcomes requires future study [9].
Heart rhythm problems and cardiovascular death
Linked to more rhythm problems at low potassium and more cardiovascular deaths at high potassium in a meta-analysis of 24 observational studies.
The numbers and sources
- Effect
- In the older general population, low potassium was associated with more supraventricular arrhythmias (RR 1.62, 95% CI 1.02 to 2.55) and high potassium with more cardiovascular deaths (RR 1.38, 1.14 to 1.66). In patients with a heart attack, high potassium was associated with more ventricular arrhythmias (RR 2.33, 1.60 to 3.38). In people with high blood pressure, a composite cardiovascular outcome was 2.6 times as frequent with hypokalemia and 1.7 times as frequent with hyperkalemia [10].
- Population
- 310,825 participants in 24 observational studies [10].
- Sources
- [10]
- Caveats
- Observational, and the studies defined low and high potassium by different cut points. The authors call for controlled trials [10].
Raising potassium to the upper part of the range
One trial found raising potassium to 4.5 to 5.0 mEq/L cut a combined count of arrhythmia events, hospital stays and deaths by 24% in people with implanted defibrillators.
The numbers and sources
- Effect
- People with a baseline plasma potassium of 4.3 mmol/L or lower were assigned to a regimen aimed at 4.5 to 5.0 mmol/L or to standard care. Over a median 39.6 months, sustained ventricular tachycardia or appropriate defibrillator therapy, unplanned hospitalization for arrhythmia or heart failure, or death occurred in 22.7% of the higher potassium group and 29.2% of the standard care group (HR 0.76, 95% CI 0.61 to 0.95). Hospitalization for hyperkalemia or hypokalemia was similar in the two groups [11].
- Population
- 1,200 people in Denmark with an implantable cardioverter-defibrillator, at high risk of ventricular arrhythmias [11].
- Sources
- [11]
- Caveats
- One open-label trial in people with an implanted defibrillator, so it does not show what a higher potassium does in people without heart disease. The regimen used potassium supplementation, a mineralocorticoid receptor antagonist or both, with dietary guidance [11].
- Why limited
- This rests on one trial, of 1,200 people. Strength counts independent studies that agree, so one trial is limited at any size.
Sources
- US Food and Drug Administration. 21 CFR 862.1600, Potassium test system. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/section-862.1600
- Centers for Disease Control and Prevention, National Center for Health Statistics. National Health and Nutrition Examination Survey 2017-2018 Laboratory Procedure Manual: Potassium, serum, Roche Cobas 6000. Performed by the University of Minnesota Advanced Research and Diagnostic Laboratory. https://wwwn.cdc.gov/nchs/data/nhanes/public/2017/labmethods/BIOPRO-J-MET-Potassium-508.pdf
- Centers for Disease Control and Prevention, National Center for Health Statistics. National Health and Nutrition Examination Survey 2015-2016 Laboratory Procedure Manual: Potassium, refrigerated serum, Beckman UniCel DxC 800 Synchron. Performed by Collaborative Laboratory Services. https://wwwn.cdc.gov/nchs/data/nhanes/public/2015/labmethods/BIOPRO_I_MET_POTASSIUM_DXC800and660i.pdf
- Alfonzo A, Harrison A, Baines R, et al. Clinical Practice Guidelines: Treatment of Acute Hyperkalaemia in Adults. UK Kidney Association. Updated July 2026. https://www.ukkidney.org/sites/default/files/documents/FINAL%20VERSION%20-%20UKKA%20CLINICAL%20PRACTICE%20GUIDELINE%20-%20MANAGEMENT%20OF%20HYPERKALAEMIA%20IN%20ADULTS%20-%20UPDATED%20JULY%202026_0.pdf
- Lott C, Truhlář A, Alfonzo A, et al. Kreislaufstillstand unter besonderen Umständen [Cardiac arrest under special circumstances]. Leitlinien des European Resuscitation Council 2021. Notfall + Rettungsmedizin. 2021. https://doi.org/10.1007/s10049-021-00891-z
- Clase CM, Carrero JJ, Ellison DH, et al. Potassium homeostasis and management of dyskalemia in kidney diseases: conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference. Kidney International. 2020. https://doi.org/10.1016/j.kint.2019.09.018
- Šupak-Smolčić V, Franin L, Antončić D, et al. Reference Intervals for Common Biochemistry and Hematology Parameters in Early Pregnancy: A Prospective Study. Diagnostics. 2025. https://doi.org/10.3390/diagnostics15040415
- Kovesdy CP, Matsushita K, Sang Y, et al. Serum potassium and adverse outcomes across the range of kidney function: a CKD Prognosis Consortium meta-analysis. European Heart Journal. 2018. https://doi.org/10.1093/eurheartj/ehy100
- Hughes-Austin JM, Rifkin DE, Beben T, et al. The Relation of Serum Potassium Concentration with Cardiovascular Events and Mortality in Community-Living Individuals. Clinical Journal of the American Society of Nephrology. 2017. https://doi.org/10.2215/CJN.06290616
- Hoppe LK, Muhlack DC, Koenig W, et al. Association of Abnormal Serum Potassium Levels with Arrhythmias and Cardiovascular Mortality: a Systematic Review and Meta-Analysis of Observational Studies. Cardiovascular Drugs and Therapy. 2018. https://doi.org/10.1007/s10557-018-6783-0
- Jøns C, Zheng C, Winsløw UCG, et al. Increasing the Potassium Level in Patients at High Risk for Ventricular Arrhythmias. New England Journal of Medicine. 2025. https://doi.org/10.1056/NEJMoa2509542
- Koseoglu M, Hur A, Atay A, Cuhadar S. Effects of hemolysis interference on routine biochemistry parameters. Biochemia Medica. 2011. https://doi.org/10.11613/BM.2011.015
- Bailey IR, Thurlow VR. Is suboptimal phlebotomy technique impacting on potassium results for primary care? Annals of Clinical Biochemistry. 2008. https://doi.org/10.1258/acb.2007.007123
- Sevastos N, Theodossiades G, Efstathiou S, et al. Pseudohyperkalemia in serum: the phenomenon and its clinical magnitude. Journal of Laboratory and Clinical Medicine. 2006. https://doi.org/10.1016/j.lab.2005.11.008