Hook effect

Abstract: Objective and importance We present a case of a giant prolactinoma with a falsely low serum prolactin concentration determined by a two-site chemiluminometric assay. Awareness of the possibility of the "high-dose hook effect" in such cases will prevent preoperative misdiagnosis. Clinical presentation A patient with a giant invasive pituitary tumor was found preoperatively to have serum prolactin of 31 ng/ml. Pathological examination of the excised tissue, however, demonstrated strong staining for prolactin. Intervention Serial dilutions of the serum disclosed hyperprolactinemia of 280,000 ng/ml, establishing the presence of the "high-dose hook effect." Treatment with pergolide (Permax; Athena Neurosciences, S. San Francisco, CA) decreased tumor size and lowered serum prolactin by more than 99%. Conclusion A "high-dose hook effect" needs to be suspected in every patient with a giant pituitary adenoma (>3 cm) and normal serum prolactin. Subsequently assaying the diluted serum will reliably disclose this phenomenon and allow correct diagnosis and therapy.

Abstract: BackgroundThe high-dose hook effect is a well-known phenomenon of two-site immunoassays including those for human chorionic gonadotrophin (hCG). We investigated the occurrence of a high-dose hook effect in six routinely available hCG assays using a sample with a total hCG concentration of approximately 3,600,000 IU/L.MethodDilutions of a sample with high hCG concentration were analysed using six common methods: Advia Centaur, Immulite 2000, Dimension RxL, Unicel DxI 800, Roche E170 and Abbott Architect. The measured concentrations and corresponding assay signals were obtained for each method. Performance was compared with manufacturer claims.ResultsFour of the tested platforms demonstrated a clear high-dose hook effect, while the other methods showed no hook effect at the highest level tested.ConclusionOur results indicate that the hook effect may occur in some hCG assays, although the risk of reporting falsely low results was in most cases at higher concentrations than those indicated in manufacturers' p...

Abstract: Large quantities of antigen in an immunoassay system impair antigen-antibody binding, resulting in low antigen determination. This is called the 'high dose hook effect'. We report this phenomenon in a patient with a large macroprolactinoma. In this patient, the correct estimate of serum prolactin (PRL) was obtained only after appropriate dilution of serum. We suggest that in order to avoid the high dose hook effect, the serum PRL be estimated in appropriate dilution in all patients with large pituitary tumours. This is particularly important when the clinical suspicion of high PRL is strong, as in women with amenorrhoea-galactorrhoea and men with long standing hypogonadism.