False-positive point-of-care urine beta human chorionic gonadotropin testing: Insights from two clinical cases

Abstract

Case one

A young woman presented to the Early Pregnancy Assessment Unit (EPAU) with abdominal pain, amenorrhoea and variably positive home-pregnancy tests. On review, a point-of-care test (POCT) for urine beta-HCG (β-HCG) was negative but a blood test using the Abbott i-STAT β-HCG POCT device was positive. Initial transvaginal ultrasound did not demonstrate an intra- or extra-uterine pregnancy. Over the following 2 months, weekly plasma POCT iSTAT β-HCG checks remained positive. After a further ultrasound suggesting a possible ectopic pregnancy, the patient underwent a diagnostic laparoscopy which was unremarkable. Post-operatively, POCT iSTAT β-HCG levels remained elevated, and a blood sample was sent for laboratory analysis revealing an undetectable β-HCG of <1.20 IU/L (reference interval 0–4).

Case two

A middle-aged woman presented to the emergency department with mons pubis pain and swelling and was admitted to the gynaecology ward for drainage of bilateral abscesses. On review, she had raised blood β-HCG levels, measured using the Abbott i-STAT POCT device. A subsequent blood sample sent for laboratory analysis showed β-HCG levels within the post-menopausal reference interval. Discussion: In both cases, POCT immunoassay interference was confirmed by consistent results produced when contemporaneous samples were analysed by different analytical platforms. Immunoassay interference, though rare, can lead to inaccurate results from POCT devices, potentially impacting patient diagnosis and management. Clinical teams should remain vigilant for this possibility; if test results do not align with clinical expectations, it is essential to promptly send a blood sample for laboratory analysis.