Hypocalcemia Differential Diagnoses

Updated: Nov 10, 2022
  • Author: Manish Suneja, MD, FASN, FACP; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Diagnostic Considerations

The first step in evaluation of hypocalcemia is to exclude factitious cases by measuring the serum albumin levels, as low serum albumin levels can cause a reduction in the total, but not the ionized, fraction of serum calcium. Patients do not have any signs or symptoms of hypocalcemia.

Each 1 g/dL reduction in the serum albumin concentration will lower the total calcium concentration by approximately 0.8 mg/dL without affecting the ionized calcium concentration. Thus, the calcium level should be corrected in patients with low serum albumin levels, using the following formula:

Corrected calcium (mg/dL) = measured total Ca (mg/dL) + 0.8 (4.0 - serum albumin [g/dL]), where 4.0 represents the average albumin level.

Note that calcium correction based on the above calculation may be inaccurate, particularly in geriatric patients. Ionized calcium levels should be obtained if hypocalcemia is considered to be clinically significant. It is also important to note that affinity of calcium for albumin is increased in the presence of alkalosis. Thus, respiratory alkalosis may cause an acute decrease in ionized calcium.

Gadodiamide and gadoversetamide, which are gadolinium-based contrast agents used in magnetic resonance imaging and angiography, may interfere with the colorimetric assays for calcium that are frequently used in hospital laboratories. This effect is not observed with other gadolinium-based agents: dimeglumine gadopentetate, gadoteridol, or gadoterate meglumine.

The interaction can result in a marked reduction in the measured calcium concentration of as much as 6 mg/dL if a blood sample is obtained soon after the imaging study. This effect is rapidly reversible as the gadolinium is excreted in the urine, and the patient has no symptoms or signs of hypocalcemia.

Awareness of this phenomenon is particularly important in patients with kidney insufficiency who may retain the contrast agent for prolonged periods. There is no reason to treat this type of hypocalcemia. [44, 45, 46]

Differential Diagnoses