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Clinical Chemistry 49: 1421-1422, 2003; 10.1373/49.8.1421
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(Clinical Chemistry. 2003;49:1421-1422.)
© 2003 American Association for Clinical Chemistry, Inc.

Letters to the Editor

Method Evaluation for Total ß-Human Chorionic Gonadotropin Using Urine and the ADVIA Centaur

Anna M. Halldorsdottir1, Mary O. Carayannopoulos1, Mary Scrivner2 and Ann M. Gronowski1,a

1 Department of Pathology, and Immunology, Division of Laboratory Medicine, Washington University, School of Medicine, 660 South Euclid Ave., Box 8118, St. Louis, MO 63110

2 Barnes-Jewish Hospital, St. Louis, MO 63110

aAuthor for correspondence. Fax 314-362-1461; e-mail gronowski{at}pathology.wustl.edu.


To the Editor:

We recently described the use of a quantitative serum human chorionic gonadotropin (hCG) assay with urine samples (1) . Quantitative urine hCG assays are important in validations of point-of-care qualitative hCG tests and in cases of suspected false-positive quantitative serum hCG results because of heterophilic antibodies (2)(3). Here, we report our study of the ADVIA Centaur® (Bayer Corporation) total-hCG (ThCG) serum assay with urine.

Recovery of hCG (US Pharmaco-peia) added to urine was >100% at all concentrations (Table 1 ). At concentrations <=200 IU/L, recovery was >130%. Urine hCG measurements <=200 IU/L were linear but were not parallel to expected amounts. For samples with results <200 IU/L, the concentration of hCG in the urine was equal to (measured concentration - 12 IU/L)/1.3.


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  		Table 1. Recovery of total ß-hCG from urine by the ADVIA Centaur.

We added hCG at final concentrations that ranged from 25 to 500 IU/L into four different matrices as follows: 1) urine from premenopausal, nonpregnant females (as above); 2) saline; 3) Bayer ThCG diluent (buffered heat-treated equine serum with EDTA, sodium azide, and preservatives); and 4) pooled serum from male subjects. Recoveries from diluent and serum were within 15% of expected amounts, whereas recoveries from saline were as great as 150%, similar to those seen in urine (Fig. 1, available as a Data Supplement accompanying the online version of this Letter at http://www.clinchem.org/content/vol49/issue8/).

Imprecision (CV) of twice-daily measurements over 10 days was 4.7%, 5.6%, and 3.6% at 38, 143, and 690 IU/L, respectively. This imprecision is similar to that seen with the Abbott AxSYM assay for urine hCG in our laboratory, which has CVs of 9.5%, 4.7%, and 7.6% at 17, 397, and 781 IU/L, respectively. Intraassay imprecision (n = 10) was 1.7%, 3.8%, and 3.9%, respectively, at these concentrations.

The detection limit was evaluated by measuring total ß-hCG in urine, from 40 premenopausal, nonpregnant females and 10 males, that presumably contained no hCG. The detection limit, calculated as the mean (SD), was 14 (3) IU/L. The detection limit stated by the manufacturer for serum is 10 IU/L.

To estimate the lower limit of the reportable range, we measured total ß-hCG in duplicate in urine with 2.5–50 IU/L hCG added. Results were linear from 15 to 50 IU/L but deviated from expected amounts at concentrations <15 IU/L. We evaluated the results by adding hCG to urine from a premenopausal, nonpregnant female at concentrations from 25 to 500 IU/L. Total ß-hCG was measured in duplicate. The assay was linear to 300 IU/L in urine samples compared with 1000 IU/L in serum.

Urine hCG results should be interpreted with caution because they vary with fluid intake. Serum-hCG-positive individuals may test negative by a urine hCG test because of very dilute urine. This is true for all urine pregnancy tests.

In conclusion, the ADVIA Centaur seems to provide an adequate detection limit for confirming results from point-of-care devices that detect hCG concentrations >=20 IU/L (4). This method could also be useful in cases of persistent low-positive serum hCG that are potentially attributable to heterophilic antibodies. Recovery of hCG added to urine is >100% at concentrations <200 IU/L. We recommend that this method, when used for urine hCG testing, be used only as a qualitative assay.


References

  1. Carayannopoulos MO, Grenache DG, Gronowski AM. Total ß-human chorionic gonadotropin measured in urine by an automated method. Clin Chem 2002;48:1796-1797.[Free Full Text]
  2. Cole LA, Tinne KM, Shahabi S, Omarani A. False-positive hCG assay results leading to unnecessary surgery and chemotherapy and needless occurrences of diabetes and coma. Clin Chem 1999;45:313-314.[Free Full Text]
  3. Cole LA. False positive hCG immunoassay results. Clin Chem 2002;48:A115.
  4. . College of American Pathologists. XL-G external comparative evaluations for laboratories 2002 2001 College of American Pathologists Northfield, IL. .



The following articles in journals at HighWire Press have cited this article:


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A. M. Ferguson, B. Ford, and A. M. Gronowski
Method Validation for Cerebral Spinal Fluid Human Chorionic Gonadotropin Measurement with the Advia Centaur(R)
Clin. Chem., August 1, 2008; 54(8): 1408 - 1409.
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