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.