Spurious increase in serum chromogranin A: the role of heterophilic antibodies

Background: The aim of the study was to examine the prevalence of heterophilic antibody (HAb) interference on serum chromogranin A (CgA) measurements. Methods: Serum CgA was measured in 672 serum samples before and following incubation in heterophilic antibody blocking tubes (HBTs). Results showing more than 3 and 5 SD percentage difference from the original result were considered to be affected by possible or definite HAb interference, respectively. All possible interferences were confirmed or excluded by non-linear or linear dilution tests. Results: Following HBT treatment, CgA concentrations fell > 3 SD percent compared with the original result in seven specimens, six of which also showed non-linear dilution (0.9%). A clinically relevant increase in serum CgA occurred in five patients (0.7%). No samples showed a significant increase of > 3 SD percent following HBT treatment. Conclusions: Interference from HAb occurred in up to 0.9% of sera tested for serum CgA. If an increased CgA result does not fit the clinical picture, pretreatment of serum in HBT tubes may prevent unwarranted investigations or therapies. Clin Chem Lab Med 2010;48:1497-9.