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

Abstract

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.

Residual Seizure Rate of Intermittent Inpatient EEG Compared to a Continuous EEG Model

“…Using pregnancy tests as reference, wherein a negative test ideally represents a 0% chance of pregnancy, a recent retrospective study at a large urban American academic medical center found a false-negative rate of just 1.6%, which was a reported cause for concern. 14 Although our results agree with consensus in the literature reporting increased cEEG seizure detection rates compared to non-cEEG, we did not take the typical route of describing increased cEEG detections; rather, we adopted a unique approach of estimating the number of seizures left behind when cEEG is not used, allowing for more direct risk assessments of not using cEEG. To assist QI initiatives elsewhere, other centers may calculate their own “seizure miss rates” using our custom-coded MATLAB residual risk estimator to assess their own institutional risk tolerance based on existing 2HELPS2B criteria and to justify potential deviations below or above the suggested 5% benchmark.…”

Power to Detect What? Considerations for Planning and Evaluating Sample Size

“…To use an example from daily life, people awaiting the results of a medical diagnostic test would not be happy if it could only detect a life-changing condition 80% of the time! Accordingly, some medical tests have very low false-negative rates (e.g., some pregnancy tests have only a 1% false-negative rate with others no higher than 5%; Bhandari, 2019 ; Kleinschmidt et al, 2021 ). Regardless of the exact approach one uses, however, it is important to justify trade-offs involved in adopting any power criterion, as with any particular value of α ( Lakens, Adolfi, et al, 2018 ).…”

Urine pregnancy testing: When does no mean maybe?

“…found an overall false negative rate of ∼1.6% out of over 11,000 patient visits. Interestingly in a subset of patients with “high‐risk complaints,” including pain, cramping, pelvic pain/cramping, and vaginal bleeding, the false negative rate was ∼3.6% 5 . The authors reported 12 ectopic pregnancies in patients with negative UPT with 83% of cases occurring in the high‐risk group.…”

“…Interestingly in a subset of patients with “high‐risk complaints,” including pain, cramping, pelvic pain/cramping, and vaginal bleeding, the false negative rate was ∼3.6%. 5 The authors reported 12 ectopic pregnancies in patients with negative UPT with 83% of cases occurring in the high‐risk group. Similarly, the authors reported that ∼75% of all “abnormal pregnancies” occurred in this high‐risk group.…”