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.


METHODS
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.


CONCLUSIONS
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.
Laboratoire d'hormonologie, CHU de Bordeaux, 33604 Pessac, France.
Nassima
N
Belaidi
Laboratoire d'hormonologie, CHU de Bordeaux, 33604 Pessac, France; Groupe de Biologie Spécialisé, Société Française de Médecine Nucléaire, 75270 Paris, France.
Agnès
A
Georges
Groupe de Biologie Spécialisé, Société Française de Médecine Nucléaire, 75270 Paris, France; Laboratoire Cerba, 95310 Saint-Ouen, l'Aumône, France.
Isabelle
I
Lacroix
Laboratoire, Groupe Hospitalier Mutualiste, Clinique des Eaux Claires, 38000 Grenoble, France.
Anne
A
Croisonnier
Département de biochimie, toxicologie et pharmacologie, CHU de Grenoble, 38043 Grenoble, France.
Véronique
V
Ducros
Laboratoire d'explorations fonctionnelles, hôpital Necker AP-HP, 75015 Paris, France.
Jean-Claude
JC
Souberbielle
Laboratoire d'hormonologie, CHU de Bordeaux, 33604 Pessac, France; Groupe de Biologie Spécialisé, Société Française de Médecine Nucléaire, 75270 Paris, France; Laboratoire Nutrition et Neurobiologie intégrée, UMR 1286, Université de Bordeaux, 33076 Bordeaux, France. Electronic address: jean-benoit.corcuff@u-bordeaux.fr.
Jean-Benoît
JB
Corcuff
D006801:Humans; D006934:Hypercalcemia / Q000097:blood*; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D014807:Vitamin D / Q000097:blood*
D010281:Parathyroid Hormone; D014807:Vitamin D
25 hydroxyvitamin D; Analytical interference; Immunoassay; Monoclonal immunoglobulin