Confirmation of congenital adrenal hyperplasia by adrenal steroid profiling of filter paper dried blood samples using ultra-performance liquid chromatography-tandem mass spectrometry.

BACKGROUND: The specificity of screening for congenital adrenal hyperplasia by direct measurement of 17-hydroxyprogesterone in filter paper dried blood spot samples by immunoassay is low and has a high false-positive rate. In order to reduce the false-positive rate of this test, we developed a rapid, robust, specific confirmatory procedure in which cortisol, 4-androstene-3,17-dione and 17-hydroxyprogesterone were measured simultaneously by ultra-performance liquid chromatography-tandem mass spectrometry. METHODS: After extraction, samples were analysed by ultra-performance liquid chromatography-tandem mass spectrometry and 17-hydroxyprogesterone was quantified accurately. Other steroids were determined using stable deuterated internal standards. In total, 25 patient blood spot samples and 92 control samples were analysed. RESULTS: The assay was linear for 17-hydroxyprogesterone, with a coefficient of determination >0.997 and imprecision ≤ 6.5%. An upper limit of normal for 17-hydroxyprogester-one of 4.45 nmol/L was established by analysing a cohort of samples from unaffected newborns. In addition, a cut-off of 3.5 for the peak areas ratio (17-hydroxyprogesterone+4-androstene-3,17-dione)/cortisol, allows confirmation of the affected steroidogenic enzyme. CONCLUSIONS: A high throughput method for the detection of steroids related to congenital adrenal hyperplasia has been developed, allowing the false-positive rate associated with screening for 17-hydroxyprogesterone by immunoassay to be determined.

Measurement of urinary free cortisol by tandem mass spectrometry and comparison with results obtained by gas chromatography-mass spectrometry and two commercial immunoassays.

BACKGROUND: Determination of urinary free cortisol (UFC) is an important adjunct for the assessment of adrenal function. In this study, we have analysed cortisol concentrations in urine samples by gas chromatography-mass spectrometry (GC-MS), liquid chromatography-tandem mass spectrometry (LC-MS/MS) and two immunoassays. The results were compared with GC-MS. The interference of cortisol ring-A metabolites in immunoassays was also assessed. METHODS: The GC-MS technique involved solvent extraction, LH-20 clean-up and derivatization. Only solid-phase extraction procedure was used for LC-MS/MS. The samples were analysed in positive electro-spray ionization mode, monitoring the transitions for cortisol and deuterated-cortisol at m/z 363.3 > 121.2 and m/z 365.3 > 122.2, respectively. Immunoassays were performed according to the manufacturer's instructions. RESULTS: When compared with GC-MS results both immunoassays (Coat-A-Count; approximately 1.9-fold, Centaur; approximately 1.6-fold) overestimated UFC concentrations. Cortisol ring-A dihydro- and tetrahydrometabolites contribute significantly to this overestimation. There was no interference by these metabolites in either GC-MS or LC-MS/MS methods. The sensitivity of the LC-MS/MS procedure was 2 nmol/L and the intra- and inter-assay variations were <5% in each quality-control sample. The comparison of the UFC results achieved by assaying the study samples with GC-MS and LC-MS/MS indicated that the agreement between the two methods was excellent (LC-MS/MS = 1.0036GC-MS - 0.0841; r2 = 0.9937). CONCLUSIONS: The interference of cortisol ring-A metabolites in immunoassays contribute to overestimation of UFC concentrations. The LC-MS/MS procedure had the sensitivity, specificity, linearity, precision and accuracy for the determination of UFC concentrations. The method is suitable for routine use provided that method-dependant reference values are established.

Measurement of urinary free cortisol using liquid chromatography-tandem mass spectrometry: comparison with the urine adapted ACS:180 serum cortisol chemiluminescent immunoassay and development of a new reference range.

BACKGROUND: The measurement of urinary free cortisol (UFC) is commonly used in the investigation of possible Cushing's syndrome. With the recent availability of liquid chromatography-tandem mass spectrometry (LC-MS/MS) in hospital laboratories, we wanted to develop a specific UFC LC-MS/MS method and compare it with our current immunoassay method and develop a new LC-MS/MS reference range if required. METHODS: A UFC LC-MS/MS method using deuterated cortisol as an internal standard was optimized using solid-phase extraction as a clean-up procedure. The multiple reaction-monitoring transitions used for the detection of cortisol and deuterated cortisol were 363.1 > 121 and 365.1 > 121.8, respectively. The method was investigated regarding precision, linearity, sensitivity, recovery and interference. UFC was measured by the in-house urine adapted ACS:180 serum cortisol immunoassay and the developed LC-MS/MS method in 110 urine samples from patients being investigated for possible Cushing's syndrome. RESULTS: The within-batch precisions (n = 25) of the LC-MS/MS method were 7.6%, 4.5% and 3.3% at 25.0 nmol/L, 49.6 nmol/L and 344.6 nmol/L, respectively; the between-batch precisions (n = 10) were 9.4%, 9.4% and 8.4%, respectively, at these concentrations. The method is sensitive down to 5 nmol/L and linear up to at least 1000 nmol/L. The method showed adequate cortisol recovery and no interference from the numerous drugs and steroids tested. The total run time for 20 samples, including sample preparation, was 120 min. A scatter plot of paired UFC measurements on the LC-MS/MS and the ACS:180 gave the equation: LC-MS/MS = 0.408 (ACS:180) + 2.65, r2 = 0.6664. The 24-h measured UFC results on 110 samples (25 men and 85 women) were positively skewed. After log transformation the data were less skewed, and following back transformation of the lower 97.5th centile, the upper limit of normal was 165 nmol/24 h. The 95th centile of the untransformed data was 146 nmol/24 h (n = 110, 25 men and 85 women). Separated by sex, the 95th centile was 152 nmol/24 h for men (n = 25) and 141 nmol/24 h for women (n = 85). CONCLUSIONS: We have developed a UFC LC-MS/MS method with a solid-phase extraction clean-up step. The method shows adequate performance and is suitable for routine laboratory use. The mixed sex (n = 110, men = 25, women = 85) reference range was up to 165 nmol/24 h or 146 nmol/24 h, depending on how the data are manipulated.

Measurement of total homocysteine in plasma and blood spots using liquid chromatography-tandem mass spectrometry: comparison with the plasma Abbott IMx method.

BACKGROUND: Current sampling for total homocysteine (tHcy) is problematic, requiring plasma separation within 15 min. The aim of this study was to develop a liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method for the measurement of tHcy in plasma and dried blood spots and to determine whether the dried blood spot concentration could be used to predict plasma concentrations of tHcy. METHODS: LC-MS/MS methodology was optimized to measure tHcy in plasma and dried blood spots. Fifty blood samples collected from heart transplant patients were used to form dried blood spots and for plasma analysis. Plasma tHcy was also measured using the Abbott IMx method and values were compared to the tHcy concentrations determined in plasma and dried blood spots using LC-MS/MS methodology. RESULTS: The plasma tHcy LC-MS/MS results compared well with the IMx values: LC-MS/MS=1.18(IMx)-0.44 (r(2)=0.915). The within-batch precision (n =10) of the plasma LC-MS/MS method was < 2.0% at 14.6 and 37.7 micromol/L, respectively; the between-batch precision (n=10) was 5.0 and 8.0%, respectively, at these concentrations. The method was found to be sensitive down to 1 micromol/L and linear up to at least 100 micromol/L. Dried blood spot LC-MS/MS results were considerably lower than the plasma IMx values (P < 0.0001): dried blood spot LC-MS/MS=0.33IMx+1.77 (r(2)=0.682). The within-batch precision (n=20) of the dried blood spot LC-MS/MS method was 7.3% and 4.7% at concentrations of 4.0 and 7.9 micromol/L, respectively; the between-batch precision was 12.6% and 7.9% at concentrations of 5.1 and 8.0 micromol/L, respectively. To assess whether dried blood spots are suitable as a screening test to predict plasma tHcy concentrations, arbitary cut-off levels were compared. If it is assumed that a plasma tHcy concentration of >15 micromol/L is raised, a dried blood spot result of >6.8 micro mol/L has a sensitivity and specificity in detecting a raised plasma tHcy of 83.3% and 96.2%, respectively, and a positive and negative predictive value of 95% and 86%, respectively, with an efficiency of 90%. Use of a dried blood spot cut-off concentration of 6.2 micromol/L for predicting high plasma tHcy concentrations (above 15 micromol/L) has a sensitivity and specificity of 95.8% and 73.1%, respectively, positive and negative predictive values of 76% and 95%, respectively, and an efficiency of 84%. CONCLUSIONS: We have developed a precise and accurate LC-MS/MS method for measuring plasma tHcy concentrations, which uses a small volume of plasma and is suitable for routine use. A satisfactory LC-MS/MS method for the measurement of tHcy in dried blood spots was also developed; this method might be useful in routine screening for raised plasma concentrations of tHcy.

Testosterone measurement by isotope-dilution liquid chromatography-tandem mass spectrometry: validation of a method for routine clinical practice.

BACKGROUND: Immunoassay is unsatisfactory for measuring the testosterone concentrations typically found in women. Bench-top tandem mass spectrometers are a viable alternative technology for measurements in the clinical laboratory. METHODS: We used stable-isotope dilution liquid chromatography-tandem mass spectrometry (ID/LC-MS/MS) to measure testosterone in plasma and serum. The sample volume was 50 muL in duplicate; preparation and analysis were carried out in a single tube, and a batch of 192 tubes was analyzed in 17.5 h. RESULTS: Intra- and interassay imprecision was <15% in the range 0.3-49 nmol/L. Recovery of testosterone added to samples at concentrations of 0.625-20 nmol/L was 96% (CV = 12%; n = 26). Six samples were serially diluted with double charcoal-stripped serum to demonstrate linearity. Correlation (r(2)) with isotope-dilution gas chromatography-mass spectrometry for 20 pools of clinical samples (range, 0.5-38.5 nmol/L) was 0.99. Correlations with our extraction RIA were 0.97 for clinical samples from men (range, 8-46.3 nmol/L) and 0.66 for samples from women (range, 0.7-3.0 nmol/L), but were 0.35 for male samples containing <3 nmol/L testosterone and 0.77 for female samples containing >8 nmol/L. Various steroids added to double charcoal-stripped serum showed no interference at the retention time of the testosterone peak. CONCLUSIONS: The ID/LC-MS/MS method has improved accuracy compared with immunoassay. The low sample volume and simplicity, rapidity, and robustness of the method make it suitable for use as a high-throughput assay in routine clinical biochemistry laboratories.