State-of-the-art of serum testosterone measurement by isotope dilution-liquid chromatography-tandem mass spectrometry.
BACKGROUND
The recent interest of clinical laboratories in developing serum testosterone assays based on isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/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-MS/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-MS/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-MS/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-MS/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-MS/MS procedures.
Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Gent University, Gent, Belgium. linda.thienpont@ugent.be
Linda M
LM
Thienpont
Katleen
K
Van Uytfanghe
Stuart
S
Blincko
Carol S
CS
Ramsay
Hui
H
Xie
Robert C
RC
Doss
Brian G
BG
Keevil
Laura J
LJ
Owen
Alan L
AL
Rockwood
Mark M
MM
Kushnir
Kelly Y
KY
Chun
Donald W
DW
Chandler
Helen P
HP
Field
Patrick M
PM
Sluss
D000293:Adolescent; D000328:Adult; D002138:Calibration; D002247:Carbon Isotopes; D002853:Chromatography, Liquid / Q000379:methods*; D005260:Female; D006801:Humans; D007006:Hypogonadism / Q000097:blood; D007201:Indicator Dilution Techniques; D008297:Male; D008875:Middle Aged; D012015:Reference Standards; D012044:Regression Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013048:Specimen Handling; D053719:Tandem Mass Spectrometry / Q000379:methods*; D013739:Testosterone / Q000097:blood*
D002247:Carbon Isotopes; D013739:Testosterone