Reducing False-Positive Pregnancy Test Results in Patients With Cancer

Abstract

OBJECTIVE To assess whether the use of a lab test specific for intact human chorionic gonadotropin (hCG) would reduce the number of false-positive pregnancy cases. METHODS From 10/21/14 – 01/20/15 and 04/01/15 – 06/02/15, all serum samples sent for pregnancy screening at a large cancer center with a value of ≥5 mIU/mL total β-hCG were frozen and stored, then re-tested using intact hCG reagent. We compared the accuracy of total β-hCG and intact hCG results for the diagnosis of clinically confirmed pregnancy. A negative test was defined as ≤14 mIU/mL, our current institutional cutoff. We also assessed a cutoff of <5 mIU/mL, a historical cutoff to rule out pregnancy. RESULTS We performed intact hCG testing on 64 patient samples, of which 34 had originally resulted positive when tested for total β-hCG. These included 21 cases of clinically confirmed pregnancy, and 13 false positive cases. No women were pregnant when their intact hCG concentration was ≤14 mIU/mL, and all pregnancies were detected at and above this concentration. Intact hCG reduced the number of false positive pregnancy tests from 13 to 1, a 92% reduction [95% Confidence Interval (CI) 64–99%], corresponding to a reduction in the false-positive rate from 38% [95% CI 22–56%] to 3% [95% CI 1–15%]. CONCLUSION The use of intact hCG reagent in cancer patients reduces the rate of false positive pregnancy tests without increasing the rate of false negative tests.

A rational diagnostic approach to the “phantom hCG” and other clinical scenarios in which a patient is thought to be pregnant but is not

“…A negative intact hCG test can be used to rule out pregnancy in patients producing only beta hCG fragments coming from a nontrophoblastic cancer. 71 It is thought that these carcinomatous tissues undergo metaplasia and become similar to poorly differentiated trophoblast cells. There is evidence that production of free β-hCG subunits by nontrophoblastic tumors is associated with poor prognosis.…”

A Case of a False-Positive Urine Pregnancy Test and Delayed Diagnosis of Obstructive Pyelonephritis

“…Urine and serum pregnancy tests that are based on an enzymelinked immunosorbent assay (ELISA) are qualitative tests that use monoclonal antibodies to detect levels of the 145 amino acid beta-subunit of human chorionic gonadotropin (hCG). Beta-hCG is also expressed by trophoblastic tumors [1,2].…”

“…False-positive results are associated with germ cell ovarian tumors, gestational trophoblastic tumors, and placental site trophoblastic tumors [8], ectopic pregnancy [8], paraneoplastic syndromes [8][9][10], urothelial bladder carcinoma with choriocarcinoma differentiation [11], lung carcinoma [3], urogenital anatomical malformations [12, tubo-ovarian abscess [2], adenomyosis [13], metastatic melanoma [14], treatment with selective serotonin reuptake inhibitor (SSRI) antidepressants [15], nephrotic syndrome [16,17], following blood transfusions [18], and in perimenopausal and postmenopausal states [19]. These false-positives can cause psychological distress for patients who believe that they may be pregnant, and can also lead to delays in medical procedures and tests for underlying diseases [1].…”

“…In this setting, a positive pregnancy test can lead to a delay in treatment or increase costs due to the need for further testing. Therefore, a false-positive pregnancy test may result in psychological and medical challenges, leading to a delay in diagnosis, patient distress, and increased costs of medical care [1].…”

Beta-HCG levels and ovarian ultrasonography results among non-pregnant women of reproductive age in Port Harcourt, Nigeria

“…Moreover, there is a lack of consensus among laboratories regarding the cut off values, leading to significant variation in reporting quantitative results [7]. Additionally, the reference limits suggested by manufacturers of commercial HCG assay kits may not align with actual clinical practice [12]. Despite these limitations, some studies support the use of β-HCG as a biomarker for ovarian cancer, particularly in advanced stages [8,9].…”