False-negative urine human chorionic gonadotropin in molar pregnancy: " The high-dose hook effect" !

Abstract

Failure to detect pregnancy in the emergency situations can have important consequences. These include missing of ectopic pregnancy (the leading cause of first-trimester pregnancy-related maternal death), administration of medications contraindicated in pregnancy, fetal radiation exposure, and medico legal problems. This in turn has led to the dictum to check for pregnancy in all women of child-bearing age group. Urine pregnancy (human chorionic gonadotropin [hCG]) test is the commonly used test to rule out pregnancy and has been reported by Griffey et al. in their study to achieve 100% sensitivity and 99.2% specificity in a clinical setting, resulting in a positive predictive value of 98.3% and a negative predictive value of nearly 100%. However, the sensitivity is influenced not only by the quantity of β hCG but on its variants that vary with different weeks of pregnancy. β hCG is present in several variant forms that change in their concentrations at different stages of pregnancy. In spite of its high sensitivity, in the presence of molar pregnancy that is associated with very high levels of β hCG it fails to detect the antigen (β hCG). This is explained by the phenomenon known as high-dose hook effect which further leads to delay in diagnosis and treatment. This can be overcome by dilution of the sample. In such cases, diagnosis will be made by serum β hCG and ultrasound (USG). Here, we present a case of gravida 2 para 1 living 1 with 2΍ months amenorrhea with bleeding p/v and pain abdomen of 20 days duration whose urine β hCG was repeatedly negative and diagnosis was made by serum β hCG and USG.