False Negative Urine Pregnancy Test: Hook Effect Revealed

Shista Priyadarshini,Fnu Manas,Sheela Prabhu

doi:10.7759/cureus.22779

Abstract

The urine pregnancy kit tests are commonly used in women of childbearing age to detect pregnancy. However, these tests may fail to detect pregnancy, rarely leading to inadvertent lab and radiation exposure. The hook-effect is a rare but important phenomenon, rendering the kit tests false negative due to an improper antigen-antibody ratio.

Highlights

Human chorionic gonadotropin is a hormone produced by the trophoblastic tissue that helps in the development of the embryo and fetal placenta [2]
The urinary kits target the beta subunit to avoid any confounding, as the alpha subunit is shared by other members of the glycoprotein family, including follicle-stimulating hormone (FSH), luteinizing hormone (LH), and thyroid-stimulating hormone (TSH)
Urine dilution prior to repeating the kit test often overcomes the “hook effect” as it reduces the antigen: antibody ratio. This manuscript aims to educate healthcare personnel about the rare but important “hook effect,” especially when the clinical picture is not congruent with the lab test. This case describes a scenario where pregnancy was missed because of inconsistent history, irregular menstruation, the patient's being unaware of her pregnancy and the results of her pregnancy test being negative as a result of "hook effect." Similar to our patient, there could be instances, as mentioned above, that can make the urine pregnancy tests (UPTs) false negative, so it should be kept in mind

Summary

Introduction

Every time a woman of child-bearing age is admitted to a hospital, it is a rule of thumb to check for pregnancy. We tend to lose our skepticism that these tests can sometimes be inaccurate and rate them above a well-performed history and physical examination. A 33-year-old Caucasian woman presented to the emergency room with severe low back pain, aggravated with minimal exertion She had a generalized limited range of movement and was unable to lie flat on her back. She had a past medical history of intravenous drug abuse (IVDU), tricuspid valve regurgitation, and methicillin-resistant Staphylococcus aureus (MRSA) endocarditis with valve replacement. She had two prior normal deliveries, a BMI of 21, and reported recent irregular menstruation (oligomenorrhea).

Discussion

Conclusions

Disclosures