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An unlikely pregnancy.

CASE DESCRIPTION

A 46-year-old woman presented for anterior cervical discectomy and fusion of C5/C6 and C6/C7 vertebrae to treat a cervical myelopathy. She had a history of anxiety disorders, epilepsy, and mild intellectual impairment. She denied any recent sexual activity, but was 2 weeks late for her menstrual cycle. A serum point-of-care human chorionic gonadotropin (hCG) test was interpreted as positive but a urine point-of-care hCG test was interpreted as negative and a quantitative serum hCG was <2 IU/L (reference interval 0-5 IU/L).

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Questions

1. What are potential causes of the discrepant hCG test results?

2. What tests can be done to investigate the discrepancy?

3. What should the physicians do about the discrepant results before proceeding with the surgery?

The answers are below.

ANSWERS

There are multiple reasons for discrepant hCG results. False-negative/decreased results can be caused by the high-dose hook effect (1) or high concentrations of specific hCG variants (2), whereas false-positive/increased results can be due to hCG-secreting malignancies (3) or pituitary hCG (4). Interfering antibodies have been implicated in both falsely increased and falsely decreased results (5). Investigations to identify the cause will vary depending on the pattern of test results. For example, to investigate a possible high-dose hook effect, sample dilution would be most appropriate. In this case, a positive serum qualitative result in conjunction with a serum quantitative result below the measuring range of the assay suggested the presence of an interfering antibody. Consistent with this hypothesis, the qualitative test result was negative after treatment of the sample with a lyophilized interfering- antibody-blocking reagent. This case demonstrates that point-of-care hCG tests can produce erroneous results due to interfering antibodies. Physicians are encouraged to contact the laboratory when discrepancies occur or when test results are not consistent with the clinical evidence.

Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article.

Authors' Disclosures of Potential Conflicts of Interest: No authors declared any potential conflicts of interest.

Role of Sponsor: The funding organizations played no role in the design of study, choice of enrolled patients, review and interpretation of data, or preparation or approval of manuscript.

References

(1.) Stickle DF, Gronowski AM, Olsen GA, Fellows PA, Avery MB, Studts DJ, Pirruccello SJ. Decreased signal intensity of Sure-Vue serum/urine qualitative hCG test at high [hCG] [Abstract]. Clin Chem 2000;46(Suppl 6):A3.

(2.) Gronowski AM, Cervinski M, Stenman UH, Woodworth A, Ashby L, Scott MG. False-negative results in point-of-care qualitative human chorionic gonadotropin (hCG) devices due to excess hCGbeta core fragment. Clin Chem 2009;55:1389-94.

(3.) Stenman UH, Alfthan H, Hotakainen K. Human chorionic gonadotropin in cancer. Clin Biochem 2004;37:549-61.

(4.) Snyder JA, Haymond S, Parvin CA, Gronowski AM, Grenache DG. Diagnostic considerations in the measurement of human chorionic gonadotropin in aging women. Clin Chem 2005;51:1830-5.

(5.) Kricka LJ. Human anti-animal antibody interferences in immunological assays. Clin Chem 1999;45:942-56.

Dina N. Greene, [1] Brian J. Hall, [1] and David G. Grenache [1] *

[1] University of Utah Health Sciences Center, Department of Pathology, Salt Lake City, UT.

* Address correspondence to this author at: Department of Pathology, University of Utah School of Medicine, ARUP Laboratories, 500 Chipeta Way, Salt Lake City, UT 84108. Fax 801-584-5207; e-mail david.grenache@path.utah.edu.

DOI: 10.1373/clinchem.2010.153064
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Article Details
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Title Annotation:the Chemical Chemist: What Is Your Guess?
Author:Greene, Dina N.; Hall, Brian J.; Grenache, David G.
Publication:Clinical Chemistry
Date:Oct 1, 2010
Words:600
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