False negative point-of-care urine pregnancy tests in an urban academic emergency department: a retrospective cohort study.

STUDY OBJECTIVE

To determine the prevalence of false negative point-of-care (POC) urine pregnancy tests among emergency department (ED) patients and among those with abdominal pain or vaginal bleeding.

METHODS

We identified all female patients, ages 14-50 years without prior hysterectomy who had a negative POC urine pregnancy test (beta subunit of human chorionic gonadotropin [β-hCG]) performed by trained clinical staff in the ED between September 1, 2017 and December 31, 2018, as well as a subgroup we defined a priori as "high risk" for early pregnancy complications based on a triage chief complaint (text) of abdominal pain or vaginal bleeding. We identified those with a positive urine β-hCG, serum β-hCG >5 mIU/mL, or a diagnosis of pregnancy within 3 months of the initial ED visit (index visit). We used structured chart review with American College of Obstetrics and Gynecology guidelines to determine pregnancy diagnosis and outcomes (ectopic, intrauterine, abnormal including spontaneous abortion, and unknown), the date of conception, and whether the pregnancy was present at the index visit.

RESULTS

Of 10,924 visits with a negative urine pregnancy test result that were screened for a pregnancy outcome, 171 (1.6%, 95% confidence interval [CI] = 1.4, 1.8) had a pregnancy present at the index visit. Diagnoses were ectopic (n = 12, 7.0%), intrauterine (n = 71, 41.5%), abnormal (n = 77, 45.0%), and unknown (n = 11, 6.4%). Of the 2732 patients with high-risk complaints, 97 (3.6%, 95% CI = 2.9, 4.3) had a pregnancy present at the index visit (relative risk of a pregnancy diagnosis 3.9, 95% CI = 2.9,5.3), including 10/12 ectopic (83%), 58/77 abnormal (75%), and 25/71 intrauterine pregnancies (35%). Serum β-hCG ranged from 2 mIU/mL to above assay (median = 119.5, interquartile range = 957.5).

CONCLUSION

Although false negative urine pregnancy tests were uncommon, multiple pregnancy diagnoses were missed, including ectopic pregnancies. False negatives were more common among patients with abdominal pain or vaginal bleeding. Concurrent serum β-hCG levels demonstrated a broad distribution.