Reducing False-Positive Pregnancy Test Results in Patients With Cancer

Obstet Gynecol. 2017 Oct;130(4):825-829. doi: 10.1097/AOG.0000000000002244.

Abstract

Objective: To assess whether the use of a laboratory test specific for intact human chorionic gonadotropin (hCG) would reduce the number of false-positive pregnancy test results.

Methods: From October 21, 2014, to January 20, 2015, and April 1, 2015, to June 2, 2015, all serum samples sent for pregnancy screening at a large cancer center with a value of 5 milli-international units/mL or greater total β-hCG were frozen and stored and then retested 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 milli-international units/mL or less, our current institutional cutoff. We also assessed a cutoff of less than 5 milli-international units/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 milli-international units/mL or less, and all pregnancies were detected at and above this concentration. Intact hCG reduced the number of false-positive pregnancy test results from 13 to 1, a 92% reduction (95% 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 patients with cancer reduces the rate of false-positive pregnancy test results without increasing the rate of false-negative test results.

Publication types

  • Evaluation Study

MeSH terms

  • Adolescent
  • Adult
  • Biomarkers, Tumor / blood*
  • Chorionic Gonadotropin, beta Subunit, Human / blood*
  • False Positive Reactions
  • Female
  • Humans
  • Middle Aged
  • Neoplasms*
  • Predictive Value of Tests
  • Pregnancy
  • Pregnancy Tests, Immunologic*
  • Young Adult

Substances

  • Biomarkers, Tumor
  • Chorionic Gonadotropin, beta Subunit, Human