Hypercalcemia (PDQ®): Supportive care - Health Professional Information [NCI] - 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:
Detection of asymptomatic metastatic disease in prostate cancer is greatly affected by the staging tests performed. Radionuclide bone scans are currently the most widely used tests for metastases to the bone, which is the most common site of distant tumor spread. Magnetic resonance imaging (MRI) is more sensitive than radionuclide bone scans but is impractical for evaluating the entire skeletal system. Some evidence suggests that serum prostate-specific antigen (PSA) levels can predict the results...
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.
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.
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.