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Hypercalcemia and elevated concentration of vitamin D: A case report too easy to be true
Nassima Belaidi1, Agnès Georges2, Isabelle Lacroix3
1Laboratoire d'hormonologie, CHU de Bordeaux, 33604 Pessac, France.
Background:
Endogenous (heterophile, human anti-animal …) antibodies are a known cause of interference in immunoassays.
Case Report:
A patient with hypercalcemia and low PTH levels was investigated. The serum 25OH vitamin D (25OHD) concentration was above the analytical range of the automated analyser (>150ng/mL) but serum dilutions were not linear. A myeloma-related monoclonal peak of immunoglobulin G (30g/L) was found.
Results:
Alternative 25OHD assays (RIA, automated analysers, mass spectrometry) all found concentrations <25ng/mL. NabTM columns (Thermo Scientific) eliminated the endogenous immunoglobulin from the serum thus allowing the initial analyser to provide correct results.
Discussion And Conclusion:
The potentially misleading point was that the apparent very high 25OHD levels were concomitant with hypercalcemia and low PTH levels thus mimicking vitamin D intoxication. Identifying assay interferences requires clinical awareness but, when suspected, one should be aware that technical tools or alternate assays are available to correct some interferences, including monoclonal immunoglobulins.
