Hypercalcemia and elevated concentration of vitamin D: A case report too easy to be true.

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.

Aldosterone determination: comparison of a RIA assay and a CLIA assay.

OBJECTIVE: To extend knowledge about the clinical performances of a new chemiluminescent immunoassay (CLIA) for aldosterone set up in available analysers. DESIGN AND PATIENTS: We compared the results of a RIA assay to those of a CLIA assay in 198 serum and 80 urine samples from patients in endocrine and hypertension departments. Furthermore, for serum samples the concordance of results for postural tests was analysed. RESULTS: RIA and CLIA aldosterone serum concentration was linearly correlated with a slope of 0.988 and an intercept of 70.4pmol/L. The variations of aldosterone serum concentration obtained with the two assays during postural tests were very consistent. There was no significant difference of aldosterone concentrations after thawing with the CLIA assay. RIA and CLIA aldosterone urine concentrations were linearly correlated with a slope of 0.787 and an intercept of -2.64nmol/L. Omitting the preservative boric acid from urine samples did not modify aldosterone concentration at least up to 48h after collection. CONCLUSION: The RIA and CLIA assays were well correlated for the most useful serum samples. It is well suited to circumvent isotopic assays with the throughput of available analysers.