In this post, I link to and excerpt from False negative point-of-care urine pregnancy tests in an urban academic emergency department: a retrospective cohort study [PubMed Abstract] [Full-Text HTML] [Full-Text PDF]. J Am Coll Emerg Physicians Open. 2021 May 1;2(3):e12427. doi: 10.1002/emp2.12427. eCollection 2021 Jun.
All that follows is from the above resource.
The Bottom Line
“False negative urine pregnancy tests in the emergency
department risk iatrogenic harm as well as delayed diagnosis
of pregnancy complications. This retrospective study found
a prevalence of 1.6%, including multiple ectopic pregnancies,
and a 3.6% rate among females presenting with abdominal
pain or vaginal bleeding.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.
1. INTRODUCTION
1.1. Background
When a patient of childbearing potential presents to an emergency department (ED), determining whether they are pregnant is of critical importance to explain symptoms, rule out life‐threatening complications, prevent iatrogenic harm, and allow a patient to make informed and timely decisions about pregnancy management. Because patient report and physical examination have limited sensitivity in early pregnancy, objective testing is routinely performed. 1 , 2 , 3 Testing methods vary by institution, but urine point‐of‐care (POC) detection of the beta subunit of human chorionic gonadotropin (β‐hCG) is one of the most common because it is non‐invasive, low cost, provides rapid results, and is routinely used at our center to screen for pregnancy. 4
1.2. Importance
Despite the widespread use of urine pregnancy tests, there is limited evidence of their real‐world performance. One recent review concluded that “no relevant health technology assessments, systematic reviews, meta‐analyses, randomized controlled trials, or evidence‐based guidelines were identified” regarding the diagnostic accuracy or clinical utility of urine pregnancy testing in the ED. 5 POC urine pregnancy testing has a reportedly high sensitivity (97%) with diagnostic thresholds of ≈20 mIU/mL. 6 However, false negative results have been reported with several case reports of patients with ectopic pregnancy, ruptured ectopic pregnancy, or molar pregnancies who had negative urine β‐hCG tests. 7 , 8 , 9
One study reported a false omission rate (FOR) of 0.34% 6 with another study reporting in abstract a false negative rate of 10.8% (95% CI; 9.3 to 12.6%) corresponding to a FOR of 0.9%. 10 Of note, the former and lower of these estimates only examined false negative results discovered at the index visit via concurrent testing, adding a potential downward bias by not including pregnancies identified in follow‐up. For example, if a patient who has a negative urine POC β‐hCG result is then diagnosed 3 weeks later with an 8‐week intrauterine pregnancy (IUP) by ultrasound, obstetric dating guidelines suggest that this index visit would have occurred a full 3 weeks after conception; however, such a delayed diagnosis would not have been identified as a false negative case by prior study methods. 6 , 11
1.3. Goals of this investigation
We sought to determine the prevalence of false negative urine pregnancy test results in a large urban ED to establish whether this test should appropriately be used to rule out pregnancy, both among a general population and among patients with symptoms concerning for early pregnancy complications. A high rate of false negative urine tests could inform clinician decisions as well as operational changes to support exclusive or more frequent serum testing. When available, we examined the concurrent serum β‐hCG level to evaluate the reason for false negative results. By identifying patients who had concurrent pregnancy testing (serum β‐hCG or ultrasound) as well as those who had pregnancy diagnosed in follow up from the ED visit, we aimed to provide a more accurate estimate of the performance of POC urine β‐hCG testing in routine clinical care.
1.3. Goals of this investigation
We sought to determine the prevalence of false negative urine pregnancy test results in a large urban ED to establish whether this test should appropriately be used to rule out pregnancy, both among a general population and among patients with symptoms concerning for early pregnancy complications. A high rate of false negative urine tests could inform clinician decisions as well as operational changes to support exclusive or more frequent serum testing. When available, we examined the concurrent serum β‐hCG level to evaluate the reason for false negative results. By identifying patients who had concurrent pregnancy testing (serum β‐hCG or ultrasound) as well as those who had pregnancy diagnosed in follow up from the ED visit, we aimed to provide a more accurate estimate of the performance of POC urine β‐hCG testing in routine clinical care.
