Received on February 25, 2008
Accepted on April 30, 2008

Endocrinology and Metabolism

State-of-the-Art of Serum Testosterone Measurement by Isotope Dilution Liquid Chromatography/Tandem Mass Spectrometry

¹ Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Gent University, Gent, Belgium
² Abbott Diagnostics, Dartford, Kent, UK
³ Abbott Diagnostics, Abbott Park, IL
⁴ Department of Biochemistry, University Hospital of South Manchester, Manchester, UK
⁵ ARUP Laboratories, Salt Lake City, UT, and Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT
⁶ ARUP Laboratories, Salt Lake City, UT
⁷ Esoterix Inc., Calabasas Hills, CA
⁸ Department of Clinical Biochemistry, Old Medical School, Leeds General Infirmary, Leeds, UK
⁹ Clinical Pathology Core Laboratory, Massachusetts General Hospital, Boston, MA

^* To whom correspondence should be addressed. E-mail: linda.thienpont{at}ugent.be.

BACKGROUND: The recent interest of clinical laboratories in developing serum testosterone assays based on isotope dilution liquid chromatography/tandem mass spectrometry (ID-LC/tandem MS) stems from the lack of accuracy of direct immunoassays. In this study, we assessed the accuracy and state of standardization (traceability) of 4 published ID-LC/tandem MS procedures in a method comparison with an ID-gas chromatography (GC)/MS reference measurement procedure listed in the database of the Joint Committee for Traceability in Laboratory Medicine.

METHODS: The study used 58 specimens from different patient categories. Each specimen was measured in triplicate (ID-LC/tandem MS) and quadruplicate (ID-GC/MS) in independent runs.

RESULTS: The testosterone concentrations by ID-GC/MS were 0.2–4.4 nmol/L (women), 0.2–2.0 nmol/L (hypogonadal man), and 10.1–31.3 nmol/L (normogonadal men). For ID-GC/MS, the CV was nearly constant, with a median of 1.0%; for ID-LC/tandem MS, it was concentration-dependent, with a median of up to 8%. Weighted Deming regression gave mean slopes, intercepts, and correlation coefficients of 0.90–1.11, -0.055–0.013 nmol/L, and 0.993–0.997, respectively. The % difference plot showed between 7% and 26% of the results outside a total error limit of 14%, with median deviations from ID-GC/MS between -9.6 and 0.4%.

CONCLUSIONS: This study demonstrated fairly good accuracy and standardization of the tested ID-LC/tandem MS procedures. Performance differences between procedures were evident in some instances, due to improper calibration and between-run calibration control. This emphasizes the need for thorough validation, including traceability, of new ID-LC/tandem MS procedures.