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Hypercalcemia (PDQ®): Supportive care - Health Professional Information [NCI] - Assessment

Laboratory Assessment

Normal serum calcium levels are maintained within narrow and constant limits, approximately 9.0 to 10.3 mg/dL (= 4.5–5.2 mEq/L or 2.25–2.57 mmol/L) for men and 8.9 to 10.2 mg/dL (= 4.4–5.1 mEq/L or 2.22–2.54 mmol/L) for women. Symptoms of hypocalcemia or hypercalcemia are caused by abnormalities in the ionized fraction of the plasma calcium concentration; however, ionized calcium levels are rarely checked routinely in clinical laboratories. The total plasma calcium is used to infer the ionized calcium fraction and is usually accurate, except in the setting of hypoalbuminemia. Because hypoalbuminemia is not uncommon among patients with cancer, it is necessary to correct the total plasma calcium concentration for the percent of calcium that would have been measured if the albumin level were within normal range. The calculation is as follows:

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total serum calcium corrected for albumin level:[(normal albumin – patient's albumin) × 0.8] + patient's measured total calcium

This calculated value is fairly accurate, except in the presence of elevated serum paraproteins, such as in multiple myeloma. In this case, laboratory measurement of the actual ionized calcium concentration may be necessary.[1]

Calcium also binds to globulins in blood. In contrast with hypoalbuminemia, hypogammaglobulinemia has a relatively small effect on calcium protein binding. Serum total calcium concentration can be corrected for changes in globulins as follows: total serum calcium concentration varies directly by 0.16 mg/dL, 0.08 mEq/L, or 0.04 mmol/L with each 1 g/dL change in globulin concentration. In clinical practice, changes in serum globulin concentrations rarely effect clinically significant changes in the ionized calcium fraction.

Acid-base status also affects the interpretation of serum calcium values. While acidosis decreases the protein-bound fraction (consequently increasing the ionized calcium fraction), alkalosis increases protein binding. Ionized calcium fraction concentration can be corrected for changes in pH as follows: ionized calcium fraction concentration varies inversely by 0.12 mg/dL, 0.06 mEq/L, or 0.03 mmol/L with each 0.1 unit change in pH. Unlike changes in serum albumin concentration, alterations in blood pH rarely effect clinically significant changes in the ionized calcium fraction.[2]

Laboratory studies

It is important to measure the serum calcium and albumin concentrations. Other selected tests (as shown below) may be useful in some instances:

  • Blood urea nitrogen and creatinine concentrations (renal function).
  • Immunoreactive parathormone (iPTH):
    • iPTH concentration is increased or rarely normal in hyperparathyroid disease.
    • iPTH is typically decreased or undetectable in hypercalcemia of malignancy.
  • Parathyroid hormone–related peptide (if available).
  • Serum 1,25-dihydroxy vitamin D concentration in patients with hematologic malignancies.
  • Other serum electrolyte concentrations (phosphate, magnesium).
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WebMD Public Information from the National Cancer Institute

Last Updated: February 25, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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