Calcium level
Total calcium counts calcium bound to protein along with the free fraction. Two US survey laboratory manuals print adult ranges of 8.4 to 10.2 and 8.5 to 10.5 mg/dL. Higher values go with slightly more deaths and heart disease in pooled studies. Formulas that correct calcium for albumin did not beat the plain total in two large laboratory studies.
- 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 calcium test systems, which measure the total calcium level in serum, as class II devices [1]. Albumin-corrected calcium is a calculated figure and ionized calcium is a separate measurement.
- Measures
- The total calcium in serum. About 40% of it is bound to proteins, 10% is in inorganic complexes and 50% is free (ionized) calcium [2].
- Also called
- calcium, serum calcium, total calcium, calcium total, calcium serum, Ca, calcium blood test
- Tested for
- bone health, parathyroid problems, kidney stones, kidney disease, vitamin D status, muscle cramps, checking a calcium 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 research2
- ModerateLinked to slightly more deaths and cardiovascular disease at higher calcium, 13% more deaths per standard deviation, in pooled studies of people without a calcium disorder.
- ModerateShown in a genetic study to go with more coronary artery disease, 25% higher odds for each 0.5 mg/dL of genetically higher calcium.
Reported risks0
No risks sourced yet.
Reference ranges
Each range is the one its source published, in mg/dL. Also reported in mmol/L. Where sources differ, each is shown.
US national survey laboratory procedure manual, 2017 to 2018
Adults aged 18 to 60, as the reference range printed for the assay · [2], [3]
| Range | What the source calls it |
|---|---|
| below 8.4 mg/dL | No name given |
| 8.4 to 10.2 mg/dL | "reference range" |
| above 10.2 mg/dL | 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). It is the range attached to that assay, not one derived from survey participants, and the manual gives no range for people older than 60 [2]. The survey's data file reports each result in both units, and its lowest and highest values, 6.4 and 11.7 mg/dL, appear as 1.6 and 2.925 mmol/L, which matches the conversion factor above [3].
US national survey laboratory procedure manual, 2015 to 2016
People older than 12, as the reference range printed for the assay · [4]
| Range | What the source calls it |
|---|---|
| below 8.5 mg/dL | No name given |
| 8.5 to 10.5 mg/dL | "reference range" |
| above 10.5 mg/dL | 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. It lists results below 7.0 or above 14.0 mg/dL as critical values that the laboratory telephones for its own patients. Two assays used by the same national survey print different ranges [4][2].
US national survey laboratory procedure manual, 2015 to 2016, children aged 2 to 12
Children aged 2 to 12 · [4]
| Range | What the source calls it |
|---|---|
| below 8.8 mg/dL | No name given |
| 8.8 to 10.8 mg/dL | "reference range" |
| above 10.8 mg/dL | 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 2 to 12 and older than 12 without saying which band a child of exactly 12 falls in [4].
US national survey laboratory procedure manual, 2015 to 2016, infants aged 10 days to 2 years
Infants and children aged 10 days to 2 years · [4]
| Range | What the source calls it |
|---|---|
| below 9 mg/dL | No name given |
| 9 to 11 mg/dL | "reference range" |
| above 11 mg/dL | No name given |
From the same manual and the same 1995 pediatric guideline for the analyzer [4].
US national survey laboratory procedure manual, 2015 to 2016, newborns under 10 days
Newborns from birth to 10 days · [4]
| Range | What the source calls it |
|---|---|
| below 7.6 mg/dL | No name given |
| 7.6 to 10.4 mg/dL | "reference range" |
| above 10.4 mg/dL | No name given |
From the same manual and the same 1995 pediatric guideline for the analyzer [4].
What has been shown to move it
Shown to lower it2
Lower blood calcium
Shown to lower blood calcium slightly, with mild drops in 18% on alendronate against 12% on placebo. The zoledronic acid label calls low calcium a significant risk in Paget's disease.
The numbers and sources
- How common
- Very common: more than 1 in 10 people.
- Effect
- Mild, transient, symptom-free drops in serum calcium occurred in about 18% on alendronate and 12% on placebo, and calcium fell about 2% from baseline in the first month. Drops below 8.0 mg/dL were similar in both groups [15]. After zoledronic acid, about 0.2% of women with osteoporosis had calcium below 7.5 mg/dL, and about 21% of people with Paget's disease had calcium below 8.4 mg/dL at 9 to 11 days [13].
- Population
- Alendronate controlled trials [15]; zoledronic acid osteoporosis and Paget's trials [13].
- Sources
- [15], [13]
- Caveats
- Both labels require low calcium and vitamin D shortage to be corrected first [15][13].
Calcium
One small study found calcium intake below reference values in adults over 12 weeks, with blood calcium falling but staying in range.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- In 35 adults with obesity, calcium intake stayed below reference values, and serum calcium fell from 2.52 to 2.36 mmol/L at 12 weeks, within the reference range [15].
- Population
- 35 adults with BMI over 30 [15].
- Sources
- [15]
- Caveats
- One small uncontrolled study. The authors link the fall to fewer legumes and less dairy, or to the high fat intake [15].
Shown to raise it3
Phosphate and parathyroid hormone
Shown to lower blood phosphate, urea and parathyroid hormone in adults with chronic kidney disease on a protein-restricted diet.
The numbers and sources
- Effect
- Ketoanalogues added to a protein-restricted diet lowered blood urea nitrogen and phosphorus and raised calcium against a low-protein diet alone [1]. In 17 RCTs, they lowered serum phosphate and parathyroid hormone [2].
- Population
- Adults with CKD not on dialysis [1][2].
- Sources
- [1], [2]
- Caveats
- These are blood markers, not fractures or heart events.
Blood calcium
Shown to raise blood calcium in adults with chronic kidney disease, mainly when paired with a low-protein diet.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Blood calcium rose with ketoanalogues against a low-protein diet alone [1]. In a second meta-analysis, calcium rose significantly only when ketoanalogues were paired with a low-protein diet, not a very low-protein diet [2].
- Population
- Adults with CKD [1][2].
- Sources
- [1], [2]
- Caveats
- The abstracts do not report how many people developed high calcium.
Long-term use
One small study: over 36 months on calcium AKG, blood calcium rose and parathyroid hormone fell in 14 dialysis patients. No long-term study in healthy people was located.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- In 14 hemodialysis patients given calcium AKG, a mean 4.5 g a day for 36 months, serum phosphate fell from 2.6 to 1.9 mmol/l, serum calcium rose from 2.2 to 2.47 mmol/l, and intact parathyroid hormone fell from 29 to 8 pmol/l [12]. The abstract does not report adverse events [12].
- Population
- 14 adults on hemodialysis [12].
- Sources
- [12]
- Caveats
- One uncontrolled study in kidney failure, where the falls in phosphate and parathyroid hormone were the aim of treatment [12]. It does not show what years of use do in healthy people.
Tested, and not shown to change it1
Calcium
Small trials found calcium intake about 290 mg a day lower than on a national guideline diet, and 60% of need on a modified version.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Calcium intake was 292 mg a day lower than on the Australian national guide diet after 4 weeks (95% CI 99 to 486) [7]. In a 3-week study, calcium intake changed unfavorably [9]. On a modified Paleolithic diet for multiple sclerosis, calcium from food averaged 60.3% of individual need, and serum calcium did not change [10].
- Population
- 39 women [7]; volunteers without known disease, 14 completing and 6 with full dietary data [9]; 19 people with progressive multiple sclerosis [10].
- Sources
- [7], [9], [10]
- Caveats
- Intake, not bone outcomes. Small studies, one uncontrolled [9].
How it compares with the reference method
Mixed results1
Published severity grades use corrected calcium
Two endocrine societies grade high calcium on albumin-adjusted calcium, so their cut points of 12 and 14 mg/dL are not ranges for the total calcium on a standard panel.
The numbers and sources
- Compared with
- Albumin-adjusted calcium, the quantity these guidelines grade
- Effect
- The Endocrine Society guideline on hypercalcemia of malignancy classifies albumin-adjusted serum calcium below 12 mg/dL (3 mmol/L) as mild, 12 to 14 mg/dL (3 to 3.5 mmol/L) as moderate and above 14 mg/dL (3.5 mmol/L) as severe [11]. UK Society for Endocrinology guidance states that calcium measurements are to be adjusted for serum albumin, and describes levels below 3.0 mmol/L as often without symptoms, 3.0 to 3.5 mmol/L as tolerated when the rise has been slow, and above 3.5 mmol/L as carrying a risk of dysrhythmia and coma [12]. Its companion guidance on low calcium states that symptoms typically develop when adjusted calcium falls below about 1.9 mmol/L, and calls severe hypocalcemia a medical emergency [13].
- Population
- Adults with hypercalcemia of malignancy [11]. Adult patients seen by non-specialists in the UK [12][13].
- Sources
- [11], [12], [13]
- Caveats
- These grades are for a calculated quantity, so this page does not place a typed total calcium against them. The Endocrine Society introduces the same cut points under the plain term serum calcium and specifies albumin-adjusted calcium in its treatment figure [11]. The UK guidance notes that the threshold for symptoms varies greatly and depends on how fast calcium falls [13].
Did not match the reference method1
Albumin-corrected calcium against ionized calcium
Not shown to match ionized calcium better than plain total calcium: in two laboratory studies of 6,549 and 5,055 samples, correction formulas added no accuracy.
The numbers and sources
- Compared with
- Ionized (free) calcium measured in the same blood sample
- Effect
- In Norwegian laboratory data, unadjusted total calcium classified calcium status more accurately than albumin-adjusted calcium in people with reduced kidney function (Harrell's c 0.801 against 0.790 for locally derived formulas and 0.791 for the top-performing formula taken from the literature). With kidney function above that level the three did not differ [8]. In a second laboratory series, calcium adjusted by the Payne formula overestimated calcium status in up to 80% of cases with low albumin or a blood pH disorder. Three other formulas improved on the Payne formula but not on total calcium [9]. The corrected figure also depends on how albumin is measured: on 165 samples, mean corrected calcium was 2.34 mmol/L with one albumin method and 2.46 mmol/L with another [10].
- Population
- 6,549 patients older than 2 with ionized calcium, total calcium, albumin, creatinine and phosphate measured in one blood draw [8]. 5,055 samples with ionized calcium, total calcium, albumin and pH measured together [9]. 165 serum samples [10].
- Sources
- [8], [9], [10]
- Caveats
- Both large studies used samples on which ionized calcium had been ordered, so they describe hospital and clinic patients more than the general population. The authors of the first propose abandoning adjustment formulas, and the authors of the second conclude that total and albumin-adjusted calcium both misclassify calcium status [8][9].
What studies tie it to
Linked in research2
Death and cardiovascular disease
Linked to slightly more deaths and cardiovascular disease at higher calcium, 13% more deaths per standard deviation, in pooled studies of people without a calcium disorder.
The numbers and sources
- Effect
- In a systematic review of studies in people selected neither for kidney disease nor for abnormal calcium, 5 of 11 studies reported a significant positive association between serum calcium and death, and 8 of 13 between serum calcium and cardiovascular disease. Pooled across 8 studies each, the hazard ratio per standard deviation of serum calcium was 1.13 (95% CI 1.09 to 1.18) for death and 1.08 (1.04 to 1.13) for cardiovascular disease. With hazard ratios adjusted for cardiovascular risk factors, the pooled figure for cardiovascular disease was 1.04 (1.01 to 1.08) [5].
- Population
- Longitudinal studies with at least 1 year of follow-up, located in a search to December 2014 [5].
- Sources
- [5]
- Caveats
- Observational. The authors state that these data cannot determine causality [5]. The abstract gives no total head count.
Coronary artery disease in a genetic study
Shown in a genetic study to go with more coronary artery disease, 25% higher odds for each 0.5 mg/dL of genetically higher calcium.
The numbers and sources
- Effect
- Using 6 gene variants related to serum calcium, the odds ratio per 0.5 mg/dL of genetically predicted higher calcium, about 1 standard deviation, was 1.25 (95% CI 1.08 to 1.45) for coronary artery disease and 1.24 (1.05 to 1.46) for heart attack [6].
- Population
- 184,305 individuals, 60,801 with coronary artery disease and 123,504 without [6].
- Sources
- [6]
- Caveats
- Mendelian randomization. The 6 variants explained about 0.8% of the variation in serum calcium. The estimate describes lifelong genetic exposure, and the authors state that whether it carries over to shorter exposures is unknown [6].
Checked, no link found1
Surgery for mildly raised calcium from an overactive parathyroid
One trial found parathyroid surgery did not reduce deaths, fractures, heart events or kidney stones over 10 years in mild primary hyperparathyroidism.
The numbers and sources
- Effect
- In people with mild primary hyperparathyroidism and modest hypercalcemia, 15 had died 10 years after randomization, 8 assigned to surgery and 7 to observation. Over an extended period to 2018 there were 44 deaths, 24 and 20. Cardiovascular events, cerebrovascular events, cancer, peripheral fractures and kidney stones numbered 52 in the surgery group and 49 in the observation group. Vertebral fractures occurred in 7 patients in each group [7].
- Population
- 191 patients at 8 Scandinavian centers, 95 assigned to parathyroidectomy and 96 to observation [7].
- Sources
- [7]
- Caveats
- One trial of 191 people, and 50 withdrew during the study. It enrolled mild disease without known complications, and the abstract does not report calcium levels after surgery [7].
Sources
- US Food and Drug Administration. 21 CFR 862.1145, Calcium test system. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/section-862.1145
- Centers for Disease Control and Prevention, National Center for Health Statistics. National Health and Nutrition Examination Survey 2017-2018 Laboratory Procedure Manual: Total Calcium, 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-Total-Calcium-508.pdf
- Centers for Disease Control and Prevention, National Center for Health Statistics. National Health and Nutrition Examination Survey 2017-2018 Data Documentation, Codebook, and Frequencies: Standard Biochemistry Profile (BIOPRO_J). February 2020. https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2017/DataFiles/BIOPRO_J.htm
- Centers for Disease Control and Prevention, National Center for Health Statistics. National Health and Nutrition Examination Survey 2015-2016 Laboratory Procedure Manual: Total Calcium, 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_CALCIUM_DXC800and660i.pdf
- Reid IR, Gamble GD, Bolland MJ. Circulating calcium concentrations, vascular disease and mortality: a systematic review. Journal of Internal Medicine. 2016. https://doi.org/10.1111/joim.12464
- Larsson SC, Burgess S, Michaëlsson K. Association of Genetic Variants Related to Serum Calcium Levels With Coronary Artery Disease and Myocardial Infarction. JAMA. 2017. https://doi.org/10.1001/jama.2017.8981
- Pretorius M, Lundstam K, Heck A, et al. Mortality and Morbidity in Mild Primary Hyperparathyroidism: Results From a 10-Year Prospective Randomized Controlled Trial of Parathyroidectomy Versus Observation. Annals of Internal Medicine. 2022. https://doi.org/10.7326/M21-4416
- Lian IA, Åsberg A. Should total calcium be adjusted for albumin? A retrospective observational study of laboratory data from central Norway. BMJ Open. 2018. https://doi.org/10.1136/bmjopen-2017-017703
- Pekar JD, Grzych G, Durand G, et al. Calcium state estimation by total calcium: the evidence to end the never-ending story. Clinical Chemistry and Laboratory Medicine. 2020. https://doi.org/10.1515/cclm-2019-0568
- Garcia Moreira V, Beridze Vaktangova N, Martinez Gago MD, et al. Overestimation of Albumin Measured by Bromocresol Green vs Bromocresol Purple Method: Influence of Acute-Phase Globulins. Laboratory Medicine. 2018. https://doi.org/10.1093/labmed/lmy020
- El-Hajj Fuleihan G, Clines GA, Hu MI, et al. Treatment of Hypercalcemia of Malignancy in Adults: An Endocrine Society Clinical Practice Guideline. The Journal of Clinical Endocrinology & Metabolism. 2023. https://doi.org/10.1210/clinem/dgac621
- Walsh J, Gittoes N, Selby P, Society for Endocrinology Clinical Committee. Society for Endocrinology Endocrine Emergency Guidance: Emergency management of acute hypercalcaemia in adult patients. Endocrine Connections. 2016. https://doi.org/10.1530/EC-16-0055
- Turner J, Gittoes N, Selby P, Society for Endocrinology Clinical Committee. Society for Endocrinology Endocrine Emergency Guidance: Emergency management of acute hypocalcaemia in adult patients. Endocrine Connections. 2016. https://doi.org/10.1530/EC-16-0056