Sodium level
Sodium is the major cation in the fluid outside cells. Two US survey laboratory manuals print adult ranges of 133 to 145 and 136 to 144 mEq/L. Lower values go with more deaths, falls and fractures, yet a trial that corrected low sodium in hospital found no fewer deaths or readmissions. Two common methods differ by about 2 mEq/L.
- 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 sodium test systems as class II devices [1]. Reports print the unit as mEq/L or mmol/L, and for sodium the two give the same number.
- Measures
- The concentration of sodium in serum or plasma. Sodium is the major positively charged ion in the fluid outside cells and maintains fluid distribution and osmotic pressure [2].
- Also called
- sodium, serum sodium, sodium serum, plasma sodium, Na, Na+, sodium blood test, natremia
- Tested for
- hydration, dehydration, electrolyte balance, low sodium, kidney function, fluid retention, confusion workup, diuretic monitoring
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 research4
- StrongLinked to about twice the odds of falls and of fractures at low sodium in two meta-analyses of observational studies.
- ModerateLinked to more deaths at low sodium, about 2.6 times the risk across 81 pooled studies, with risk rising as sodium fell.
- ModerateLinked to more deaths at high sodium in intensive care and in chronic kidney disease, with the odds reaching 3.6 times above 155 mEq/L.
- LimitedOne US cohort linked midlife sodium above 142 mEq/L to 39% more chronic disease, and above 144 mEq/L to 21% more early deaths, over 25 years.
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 assay · [2], [3]
| Range | What the source calls it |
|---|---|
| below 133 mEq/L | No name given |
| 133 to 145 mEq/L | "reference range" |
| above 145 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). It is the range attached to that assay, not one derived from survey participants [2]. The manual prints the range in mmol/L. For sodium that is the same number as mEq/L: the 2015 to 2016 manual labels the survey's sodium 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 136 mEq/L | No name given |
| 136 to 144 mEq/L | "reference range" |
| above 144 mEq/L | No name given |
From the manual for the method used in the 2015 to 2016 survey (Beckman UniCel DxC 800, indirect ion-selective electrode, 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. It lists results below 115 or above 160 mEq/L as critical values that the laboratory telephones for its own 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 135 mEq/L | No name given |
| 135 to 143 mEq/L | "reference range" |
| above 143 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 132 mEq/L | No name given |
| 132 to 143 mEq/L | "reference range" |
| above 143 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 131 mEq/L | No name given |
| 131 to 145 mEq/L | "reference range" |
| above 145 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, newborns under 1 month
Newborns from birth to 1 month · [3]
| Range | What the source calls it |
|---|---|
| below 131 mEq/L | No name given |
| 131 to 143 mEq/L | "reference range" |
| above 143 mEq/L | No name given |
From the same manual and the same 1995 pediatric guideline for the analyzer [3].
European clinical practice guideline on hyponatremia, 2014
People with low sodium, graded by how far the concentration has fallen · [4], [5]
| Range | What the source calls it |
|---|---|
| below 125 mEq/L | "profound" A doctor, immediately |
| 125 to 129 mEq/L | "moderate" |
| 130 to 135 mEq/L | "mild" |
| above 135 mEq/L | No name given |
A joint guideline of the European Society of Intensive Care Medicine, the European Society of Endocrinology and the European Renal Association. It defines hyponatremia as a serum sodium below 135 mmol/L and grades it by the concentration measured with an ion-specific electrode. It prints the mild band as 130 to 135, so a result of exactly 135 sits on the edge of the guideline's own definition. It grades symptoms and speed of onset separately. It covers low sodium only, so this block does not classify high results. The guideline states that hyponatremia is associated with increased illness, death and length of hospital stay [4]. The bands were read in the guideline group's own Spanish-language publication of 2017, which prints them as leve, moderada and grave. The English words mild, moderate and profound are as given in a case report that reproduces the group's table [5].
Funk and colleagues, Austrian intensive care cohort, 2010
Adults on admission to an intensive care unit · [6]
| Range | What the source calls it |
|---|---|
| below 125 mEq/L | "severe hyponatremia" A doctor, immediately |
| 125 to 129 mEq/L | "mild hyponatremia" |
| 130 to 134 mEq/L | "borderline hyponatremia" |
| 135 to 145 mEq/L | "normal sodium levels" |
| 146 to 150 mEq/L | "borderline hypernatremia" |
| 151 to 155 mEq/L | "mild hypernatremia" |
| above 155 mEq/L | "severe hypernatremia" A doctor, immediately |
Grades defined by the authors of a study of 151,486 adults admitted to 77 Austrian intensive care units, to test whether sodium on admission predicted death in hospital. The paper prints the bands as inequalities, such as 125 or above and below 130, which this block writes in whole numbers. Its mild band (125 to 129) is the band the European guideline calls moderate, and it is the only source on this page that grades high sodium. Every grade outside 135 to 145 was associated with more deaths in hospital [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 133 mEq/L | No name given |
| 133 to 139 mEq/L | "reference interval" |
| above 139 mEq/L | No name given |
The central 95% of results in 299 women with singleton pregnancies at one Croatian center, measured by indirect ion-selective electrode on a Roche Cobas 6000. The authors compare it with the 137 to 146 mmol/L range that Croatian laboratories use for non-pregnant women and judge sodium to be lower in early pregnancy by a clinically relevant amount. The study covers the first trimester only [7].
What has been shown to move it
Shown to lower it4
Low sodium
Linked to low blood sodium in about 6% of SNRI users in observational studies, at about twice the odds of non-users.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- Across 38 observational studies, hyponatremia occurred in 6.13% of people on SNRIs, with an odds ratio of 2.270. Venlafaxine ranked highest among SNRIs and duloxetine lower [38]. An earlier review found incidence figures from 0.08% to 70% for venlafaxine depending on study design and cutoff, and named older age and thiazide diuretics as risk factors [39].
- Population
- 30 cohort and 8 case-control studies [38]; 21 effect studies and more than 100 case reports [39].
- Sources
- [38], [39]
- Caveats
- Observational, with rates that swing widely by population and sodium cutoff. The abstract of [38] gives no confidence intervals.
Low sodium
Linked to low blood sodium in about 6% of users in observational studies, at about twice the odds of non-users, more often in older adults.
The label reports cases with sodium below 110 mmol/L and states that older people and people on diuretics may be at greater risk.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- Across 38 observational studies, hyponatremia occurred in 5.98% of people on SSRIs, with an odds ratio of 2.158 against comparison groups. Among individual drugs, fluoxetine ranked highest and sertraline lower [45]. An earlier review found incidence figures from 0.06% to 40% for SSRIs depending on design and cutoff, and named older age (OR 6.3) and thiazide diuretics (OR 11.2 to 13.5) as risk factors [46]. The label reports cases with sodium below 110 mmol/L and states that older people and people on diuretics may be at greater risk [24].
- Population
- 30 cohort and 8 case-control studies [45]; 21 effect studies and more than 100 case reports [46].
- Sources
- [45], [46], [24]
- Caveats
- Observational, with rates that swing widely by population and by the sodium cutoff used [46]. The abstract of [45] gives no confidence intervals.
Low sodium
Linked to low blood sodium in about 3.5% of new users over 2 years, about 1.4 percentage points more than on comparison drugs.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- In a Danish cohort, the 2-year cumulative incidence of sodium below 130 mmol/L was 3.51% in new users of hydrochlorothiazide combined with a renin-angiotensin drug, 1.38 percentage points more than on the renin-angiotensin drug alone (95% CI 1.01 to 1.75). For bendroflumethiazide it was 3.83%, 1.35 points more than on a calcium channel blocker. The excess was largest in the first 30 days (HR 4.25 and 3.56) and rose with age and illness [18]. In a US cohort, hyponatremia was more frequent on chlorthalidone than on hydrochlorothiazide (HR 1.31, 95% CI 1.16 to 1.47) [8].
- Population
- 11,943 new users of hydrochlorothiazide with a renin-angiotensin drug and 85,784 of the renin-angiotensin drug alone, and 37,786 new users of bendroflumethiazide against 44,963 of a calcium channel blocker, all aged 40 or older [18]; 730,225 first-time users [8].
- Sources
- [18], [8]
- Caveats
- Observational. The authors note residual confounding is likely [18].
Low sodium
Linked to low sodium, reported in 9.2% of bumetanide patients tested. The labels warn of low sodium and other electrolyte losses.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- Low sodium was reported in 9.2% of patients tested on bumetanide, alongside low chloride in 14.9% [15]. The furosemide label lists low sodium, low chloride alkalosis, low potassium, low magnesium and low calcium among the imbalances to watch for [10].
- Population
- Bumetanide-treated patients [15]; label statements [10].
- Sources
- [15], [10]
- Caveats
- No placebo comparison for these rates.
How it compares with the reference method
Mixed results1
High blood glucose
One small experiment found measured sodium fell about 2.4 mEq/L for each 100 mg/dL rise in blood glucose in 6 volunteers.
The numbers and sources
- Compared with
- Sodium in the same people as glucose was raised and lowered
- Effect
- When glucose was raised above 600 mg/dL by infusion, serum sodium fell a mean 2.4 mEq/L for every 100 mg/dL rise in glucose, more than the 1.6 mEq/L correction factor then in common use (P = 0.02). The relation was not linear: up to 400 mg/dL the 1.6 factor fit, and above 400 mg/dL a factor of 4.0 fit better [18]. The European guideline uses 2.4 mmol/L per 100 mg/dL of glucose above 100 mg/dL to estimate a corrected sodium, and lists high glucose among the causes of low sodium that is not hypotonic [4].
- Population
- 6 volunteers given somatostatin to block insulin release and 20% dextrose to raise glucose [18].
- Sources
- [18], [4]
- Caveats
- Six people in one short experiment. The authors describe the fall as a physiologic decrease in sodium concentration, not a laboratory error, and the study states no threshold for agreement [18].
Did not match the reference method1
Indirect against direct measurement
Shown to differ by method: the indirect method used on most large analyzers read 1.9 mEq/L higher on average than the direct method in 231 people.
The numbers and sources
- Compared with
- Direct ion-selective electrode measurement of the same blood
- Effect
- In 878 paired measurements, the indirect method read a mean 1.9 mmol/L higher than the direct method (95% limits -3.2 to 6.9), and the gap widened as sodium rose [15]. In a hospital study, the two methods were predicted to disagree by 4 mmol/L or more in 25% of intensive care samples and 8% of samples hospital wide. Almost all of the intensive care disagreements (97%) were in samples with low protein, where the indirect method tended to read higher [16]. A review explains that the indirect method dilutes the sample first, so raised lipid or protein gives a falsely low sodium [17]. Both survey manuals above used the indirect method, and one notes that gross lipemia can result in pseudohyponatremia [2].
- Population
- 140 patients and 91 volunteers measured during a hypertonic saline test [15]. 346 specimens chosen for low, normal or high protein, extrapolated to 48,033 routine assays over 3 months [16].
- Sources
- [15], [16], [17], [2]
- Caveats
- The paired measurements were made while sodium was being raised by a salt infusion [15]. The hospital figures are projections from selected specimens to all samples [16]. A laboratory report does not usually say which method was used.
What studies tie it to
Linked in research4
Death from any cause at low sodium
Linked to more deaths at low sodium, about 2.6 times the risk across 81 pooled studies, with risk rising as sodium fell.
The numbers and sources
- Effect
- In a meta-analysis of 81 studies, people with hyponatremia had a higher risk of death from any cause than people without it (RR 2.60, 95% CI 2.31 to 2.93). The association held in heart attack (RR 2.83), heart failure (2.47), cirrhosis (3.34), lung infections (2.49) and hospitalized patients (2.48). People who died had a mean sodium 4.8 mmol/L lower than survivors (130.1 against 134.9 mmol/L) [8]. In US veterans with chronic kidney disease, the adjusted hazard ratio for death was 1.93 (95% CI 1.83 to 2.03) below 130 mEq/L and 1.28 (1.26 to 1.30) at 130 to 135.9 mEq/L, against 136 to 145 mEq/L [9]. On admission to intensive care, the adjusted odds of death in hospital were 1.32 (1.25 to 1.39) at 130 to 134 mmol/L, 1.89 (1.71 to 2.09) at 125 to 129 and 1.81 (1.56 to 2.10) below 125 [6].
- Population
- 850,222 patients in 81 studies, 17.4% of them hyponatremic [8]. 655,493 US veterans with chronic kidney disease not on dialysis, followed for a median of 5.5 years [9]. 151,486 adults admitted to 77 Austrian intensive care units from 1998 to 2007 [6].
- Sources
- [8], [9], [6]
- Caveats
- Observational, and most of the people studied were already ill. The authors of a later trial write that it remains unclear whether hyponatremia itself increases illness and death or is an indicator of the severity of the underlying disease [10].
Falls and fractures at low sodium
Linked to about twice the odds of falls and of fractures at low sodium in two meta-analyses of observational studies.
The numbers and sources
- Effect
- In a meta-analysis of 15 studies, hyponatremia was associated with more falls (OR 2.14, 95% CI 1.71 to 2.67). The odds were already higher when the cut-off for hyponatremia was 135 mmol/L (OR 1.26, 1.23 to 1.29). Hyponatremia was also associated with more fractures, particularly hip fractures (OR 2.00, 1.43 to 2.81) [12]. A second meta-analysis found more fractures with hyponatremia in studies that reported odds ratios (OR 1.99, 95% CI 1.50 to 2.63) and in studies that reported hazard ratios (HR 1.62, 1.28 to 2.05) [13].
- Population
- 51,879 patients in 15 studies, 2,329 of them hyponatremic [12]. 212,889 participants in 15 observational studies, 12 of them pooled [13].
- Sources
- [12], [13]
- Caveats
- Observational. The authors of one review write that it is unclear whether hyponatremia is directly associated with fracture or is a surrogate marker of other causes, and call for studies of fracture risk after hyponatremia is corrected [13].
Death from any cause at high sodium
Linked to more deaths at high sodium in intensive care and in chronic kidney disease, with the odds reaching 3.6 times above 155 mEq/L.
The numbers and sources
- Effect
- On admission to intensive care, the adjusted odds of death in hospital were 1.48 (95% CI 1.36 to 1.61) at 146 to 150 mmol/L, 2.32 (1.98 to 2.73) at 151 to 155 and 3.64 (2.88 to 4.61) above 155, against 135 to 145 mmol/L [6]. In US veterans with chronic kidney disease, the adjusted hazard ratio for death was 1.33 (1.28 to 1.38) at 145.1 to 150 mEq/L and 1.56 (1.33 to 1.83) at 150 mEq/L or above, against 136 to 145 mEq/L. Mortality was lowest at 140 mEq/L [9].
- Population
- 151,486 adults admitted to Austrian intensive care units, 6.9% of them with sodium above 145 mmol/L [6]. 655,493 US veterans with chronic kidney disease not on dialysis [9].
- Sources
- [6], [9]
- Caveats
- Observational, in people who were critically ill or had kidney disease. These studies cannot say whether high sodium caused the deaths or marked the illness behind it.
Sodium at the upper end of the range in midlife
One US cohort linked midlife sodium above 142 mEq/L to 39% more chronic disease, and above 144 mEq/L to 21% more early deaths, over 25 years.
The numbers and sources
- Effect
- Sodium above 142 mmol/L in middle age was associated with a higher risk of developing chronic diseases (HR 1.39, 95% CI 1.18 to 1.63) and with higher odds of a biological age above chronological age (OR 1.50, 1.14 to 1.96). Sodium above 144 mmol/L was associated with a higher risk of premature death (HR 1.21, 1.02 to 1.45) [14].
- Population
- 15,752 adults aged 45 to 66 at enrollment in the Atherosclerosis Risk in Communities study, followed for 25 years [14].
- Sources
- [14]
- Caveats
- One cohort, observational. The authors used serum sodium as a proxy for hydration habits and state that intervention studies are needed to confirm a link between hydration and aging. These values sit inside both laboratory reference ranges at the top of this page [14].
Mixed results1
Death and readmission after low sodium is corrected
Mixed results: pooled observational studies linked a rise in low sodium to fewer deaths, while a 2,173-person trial of targeted correction found no fewer deaths or readmissions.
The numbers and sources
- Effect
- In a meta-analysis of 15 studies, any improvement of hyponatremia was associated with a lower risk of death (OR 0.57, 95% CI 0.40 to 0.81). The association was stronger in the 8 studies that set the threshold for improvement at above 130 mmol/L (OR 0.51, 0.31 to 0.86) [11]. In a randomized trial in hospitalized patients with sodium below 130 mmol/L, a targeted correction program brought sodium to 135 to 145 mmol/L in 60.4% of patients, against 46.2% with routine care. Death or readmission within 30 days occurred in 20.5% and 21.8% (difference -1.3 percentage points, 95% CI -4.9 to 2.2). Death occurred in 8.0% of each group [10].
- Population
- 13,816 patients in 15 studies [11]. 2,173 hospitalized patients at 9 European centers, median age 73, median sodium 127 mmol/L at entry [10].
- Sources
- [11], [10]
- Caveats
- The pooled studies were not randomized, so people whose sodium rose may have differed in other ways from those whose sodium did not [11]. The trial counted outcomes for 30 days and tested one program of correction in hospital. Overcorrection occurred in 2.3% of the intervention group and 1.4% of the control group, and no case of osmotic demyelination syndrome was observed [10].
Sources
- US Food and Drug Administration. 21 CFR 862.1665, Sodium test system. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/section-862.1665
- Centers for Disease Control and Prevention, National Center for Health Statistics. National Health and Nutrition Examination Survey 2017-2018 Laboratory Procedure Manual: Sodium, 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-Sodium-508.pdf
- Centers for Disease Control and Prevention, National Center for Health Statistics. National Health and Nutrition Examination Survey 2015-2016 Laboratory Procedure Manual: Sodium, 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_SODIUM_DXC800and660i.pdf
- Spasovski G, Vanholder R, Allolio B, et al. Guía de práctica clínica sobre el diagnóstico y tratamiento de la hiponatremia [Hyponatraemia diagnosis and treatment clinical practice guidelines]. Nefrología. 2017. https://doi.org/10.1016/j.nefro.2017.03.021
- John V, Evans P, Kalhan A. Delayed dyskinesia and prolonged psychosis in a patient presenting with profound hyponatraemia. Endocrinology, Diabetes & Metabolism Case Reports. 2017. https://doi.org/10.1530/EDM-16-0147
- Funk GC, Lindner G, Druml W, et al. Incidence and prognosis of dysnatremias present on ICU admission. Intensive Care Medicine. 2010. https://doi.org/10.1007/s00134-009-1692-0
- 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
- Corona G, Giuliani C, Parenti G, et al. Moderate Hyponatremia Is Associated with Increased Risk of Mortality: Evidence from a Meta-Analysis. PLoS ONE. 2013. https://doi.org/10.1371/journal.pone.0080451
- Kovesdy CP, Lott EH, Lu JL, et al. Hyponatremia, Hypernatremia, and Mortality in Patients With Chronic Kidney Disease With and Without Congestive Heart Failure. Circulation. 2012. https://doi.org/10.1161/CIRCULATIONAHA.111.065391
- Refardt J, Potasso L, Pelouto A, et al. A Randomized Trial of Targeted Hyponatremia Correction in Hospitalized Patients. NEJM Evidence. 2026. https://doi.org/10.1056/EVIDoa2500086
- Corona G, Giuliani C, Verbalis JG, et al. Hyponatremia Improvement Is Associated with a Reduced Risk of Mortality: Evidence from a Meta-Analysis. PLOS ONE. 2015. https://doi.org/10.1371/journal.pone.0124105
- Corona G, Norello D, Parenti G, et al. Hyponatremia, falls and bone fractures: A systematic review and meta-analysis. Clinical Endocrinology. 2018. https://doi.org/10.1111/cen.13790
- Upala S, Sanguankeo A. Association Between Hyponatremia, Osteoporosis, and Fracture: A Systematic Review and Meta-analysis. The Journal of Clinical Endocrinology & Metabolism. 2016. https://doi.org/10.1210/jc.2015-4228
- Dmitrieva NI, Gagarin A, Liu D, et al. Middle-age high normal serum sodium as a risk factor for accelerated biological aging, chronic diseases, and premature mortality. eBioMedicine. 2023. https://doi.org/10.1016/j.ebiom.2022.104404
- Refardt J, Sailer CO, Chifu I, et al. The challenges of sodium measurements: indirect versus direct ion-selective method. European Journal of Endocrinology. 2019. https://doi.org/10.1530/EJE-19-0101
- Dimeski G, Morgan TJ, Presneill JJ, Venkatesh B. Disagreement between ion selective electrode direct and indirect sodium measurements: Estimation of the problem in a tertiary referral hospital. Journal of Critical Care. 2012. https://doi.org/10.1016/j.jcrc.2011.11.003
- Fortgens P, Pillay TS. Pseudohyponatremia Revisited: A Modern-Day Pitfall. Archives of Pathology & Laboratory Medicine. 2011. https://doi.org/10.5858/2010-0018-RS.1
- Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia. The American Journal of Medicine. 1999. https://doi.org/10.1016/S0002-9343(99)00055-8