Correlation of Insulin-Like Growth Factor-I and -II Concentrations at Birth Measured by Mass Spectrometry and Growth from Birth to Two Months.

BACKGROUND: Immunoassays used to measure insulin-like growth factor (IGF)-I and -II concentrations are susceptible to interference from IGF-binding proteins. The aim of this study was to investigate the association of IGF-I and -II concentrations at birth with neonatal anthropometry using a liquid chromatography/mass spectrometry (LCMS) assay. METHODS: LCMS was used to measure IGF-I and -II concentrations in umbilical cord blood of term, healthy infants enrolled in the Cork BASELINE Birth Cohort Study. Weight, length, and occipitofrontal head circumference (OFC) were measured at birth and 2 months. RESULTS: Cord blood IGF-I and -II concentrations were measured in 1,100 infants. Mean (SD) IGF-I and -II concentrations were 52.5 (23.9) ng/mL and 424.3 (98.2) ng/mL, respectively. IGF-I and -II concentrations at birth were associated (p < 0.05) with weight (R2 = 0.19, R2 = 0.01), length (R2 = 0.07, R2 = 0.004), and OFC (R2 = 0.03, R2 = 0.04) at birth. Low IGF-I concentrations at birth were associated with increases in weight (p < 0.001) and OFC (p < 0.01) Z-scores in the first 2 months. CONCLUSION: Using an LCMS assay, we have shown that anthropometric parameters at birth are associated with IGF-I and weakly with IGF-II concentrations. This indicates that, at the time of birth, IGF-I is the more important growth factor for regulating infant growth.

Discordance between mass spectrometry and immunometric IGF-1 assay in pituitary disease: a prospective study.

PURPOSE: Measuring IGF-1, a biomarker for GH activity, is critical to evaluating disordered hypothalamic-pituitary GH axis. Inconsistent IGF-1 measurements among different immunoassays are well documented. We switched from Immulite 2000 immunoassay to narrow-mass-extraction, high-resolution liquid chromatography mass-spectrometry (LC-MS) compliant with recent consensus recommendations on assay standardization. Comparability of these two assays in patients with pituitary disease in a clinical practice setting is not known. We sought to compare IGF-1 levels on Immulite 2000 and LC-MS in samples from naïve and treated patients with secretory and non-secretory pituitary masses. METHODS: We prospectively collected serum samples from 101 patients treated at the Cedars-Sinai Pituitary Center between February 2012 and March 2014. We intentionally recruited more patients with acromegaly or GH deficiency to ensure a clinically representative cohort. Samples were classified as in or out of the respective reference ranges. Bland-Altman analysis was used to assess agreement between assays. RESULTS: Twenty-four percent of samples were classified differently as below, in, or above range. Agreement between the assays was poor overall, with a significant bias for immunoassay reporting higher values than LC-MS. This pattern was also observed in patients with acromegaly and those with ≥ 2 pituitary hormone deficiencies. CONCLUSIONS: IGF-1 results may differ after switching from an older immunoassay to a consensus-compliant assay such as LC-MS. Clinicians should consider the potential impact of assay switching before altering treatment due to discrepant results, particularly in patients monitored over time, such as those with acromegaly and GH deficiency.

Total and free cortisol levels during 1 µg, 25 µg, and 250 µg cosyntropin stimulation tests compared to insulin tolerance test: results of a randomized, prospective, pilot study.

PURPOSE: The appropriate cosyntropin dose during cosyntropin stimulation tests remains uncertain. We conducted a prospective, randomized pilot study to compare 1 µg IV low dose cosyntropin test, 25 µg IM medium dose cosyntropin test, and 250 µg IM standard dose cosyntropin test to evaluate secondary adrenal insufficiency. Insulin tolerance test was used as the gold standard. METHOD: The study included patients with hypothalamic/pituitary disease (n = 10) with at least one pituitary axis deficiency other than ACTH deficiency and controls (n = 12). All tests were done in random order. Sensitivity and specificity were calculated for total cortisol and serum free cortisol cut-off levels during cosyntropin stimulation tests. RESULTS: The median (range) age and F/M sex ratios for patients and controls were 54 years (23-62), 2/8, and 33 years (21-51), 6/6, respectively. The best total cortisol cut-off during low dose cosyntropin test, medium dose cosyntropin test, 30 min and 60 min standard dose cosyntropin test were 14.6 µg/dL (100% sensitivity & specificity), 18.7 µg/dL (100% sensitivity, 88% specificity), 16.1 (100% sensitivity & specificity), and 19.5 µg/dL (100% sensitivity & specificity), respectively. There was no difference in the ROC curve for cortisol values between the cosyntropin stimulation tests (p > 0.41). Using a cortisol cut-off of 18 µg/dL during cosyntropin stimulation tests, only cortisol level at 30 min during standard dose cosyntropin test provided discrimination similar to insulin tolerance test. The best peak free cortisol cut-off levels were 1 µg/dL for insulin tolerance test, 0.9 µg/dL for low dose cosyntropin test, 0.9 µg/dL for medium dose cosyntropin test, and 0.9 µg/dL and 1.3 µg/dL for 30 min and 60 min standard dose cosyntropin test, respectively. CONCLUSION: All cosyntropin stimulation tests had excellent correlations with insulin tolerance test, when appropriate cut-offs were used. This pilot study does not suggest an advantage in using 25 µg cosyntropin dose during the cosyntropin stimulation test. A serum free cortisol cut-off of 0.9 µg/dL may be used as pass criterion during low dose cosyntropin test, standard dose cosyntropin test cosyntropin test, and 30 min standard dose cosyntropin test.

Mutational Analysis in Pediatric Thyroid Cancer and Correlations with Age, Ethnicity, and Clinical Presentation.

BACKGROUND: Well-differentiated thyroid cancer (WDTC) incidence in pediatrics is rising, most being papillary thyroid carcinoma (PTC). The objective of the study was to assess the prevalence of different mutations in pediatric WDTC and correlate the genotype with the clinical phenotype. METHODS: This is a single-center retrospective study. Thyroid tissue blocks from 42 consecutive pediatric WDTC patients who underwent thyroidectomy between 2001 and 2013 were analyzed at Quest Diagnostics for BRAF(V600E), RAS mutations (N,K,H), and RET/PTC and PAX8/PPARγ rearrangements, using validated molecular methods. Thyroid carcinomas included PTC, follicular thyroid carcinoma (FTC), and follicular variant of PTC (FVPTC). RESULTS: Thirty-nine samples (29 females) were genotyped. The mean age at diagnosis was 14.7 years (range 7.9-18.4 years), and most were Hispanic (56.4%) or Caucasian (35.9%). The mean follow-up period was 2.9 years. Mutations were noted in 21/39 (53.8%), with both BRAF(V600E) (n = 9), and RET/PTC (n = 6) detected only in PTC. Mutations were detected in 2/5 FTC (PAX8/PPARγ and NRAS) and 3/6 FVPTC cases (PAX8/PPARγ). Of 28 PTC patients, 57.1% had mutations: 32.1% with BRAF(V600E), 21.4% with RET/PTC, and 3.6% with NRAS. Of patients with BRAF(V600E), 77.8% were Hispanic and 88.9% were >15 years, while all RET/PTC-positive patients were ≤15 years (p = 0.003). Tumor size, lymph node involvement, and distant metastasis at diagnosis (or soon after (131)I ablation) did not vary significantly based on the mutation. CONCLUSIONS: BRAF(V600E) was the most common mutation, especially in older and Hispanic adolescents. A larger, ethnically diverse pediatric cohort followed long term will enable the genotypic variability, clinical presentation, and response to therapy to be better assessed.

Injectable dexamethasone sodium phosphate administered orally? A pharmacokinetic analysis of a common emergency department practice.

BACKGROUND: The injectable formulation of dexamethasone has been administered orally, for the treatment of pediatric asthma and croup. The practice is followed in emergency departments around the country, but pharmacokinetic data supporting this practice are lacking. OBJECTIVES: This study evaluated the relative bioavailability and pharmacokinetics of dexamethasone sodium phosphate for injection (DSPI) administered orally compared to dexamethasone oral concentrate (DOC) in healthy adults. METHODS: This was an open label, crossover study of 11 healthy adults 18 to 45 years of age. All subjects received 8 mg of dexamethasone oral concentrate initially. After a 1-week wash-out period, subjects received 8 mg of DSPI administered orally. Dexamethasone levels were measured by liquid chromatography in tandem mass spectrometry. Cmax and area under the curve (AUC (0-t) and AUC (0-∞)) were calculated and compared between groups using the paired t test. RESULTS: The mean ± SD AUC(0-t) for dexamethasone oral concentrate and DSPI were 5497.23 ± 1649 and 4807.82 ± 1971) ng/dL/hr, respectively; 90% confidence interval (CI) was 78.8%-96.9%. The mean ± SD AUC(0-∞) for dexamethasone oral concentrate and DSPI were 6136.43 ± 2577 and 5591.48 ± 3075 ng/dL/hr, respectively; 90% CI was 79.0% -105.2%. Mean Cmax ± SD for DOC and DSPI were 942.94 ± 151 and 790.92 ± 229 ng/dL, respectively; 90% CI 76.8%-91.7%. The relative bioavailability of DSPI administered orally was 87.4% when using AUC(0-t) and 91.1% when using AUC(0-∞). The calculated absolute bioavailability was 75.9%. CONCLUSIONS: DSPI is not bioequivalent to dexamethasone oral concentrate when administered orally. The existing literature supports the efficacy of DSPI despite this. Dosing adjustments may be considered.

Temporal relationship between vitamin D status and parathyroid hormone in the United States.

BACKGROUND: Interpretation of parathyroid hormone (iPTH) requires knowledge of vitamin D status that is influenced by season. OBJECTIVE: Characterize the temporal relationship between 25-hydroxyvitamin D3 levels [25(OH)D3] and intact iPTH for several seasons, by gender and latitude in the U.S. and relate 25-hydrovitamin D2 [25(OH)D2] levels with PTH levels and total 25(OH)D levels. METHOD: We retrospectively determined population weekly-mean concentrations of unpaired [25(OH)D2 and 25(OH)D3] and iPTH using 3.8 million laboratory results of adults. The 25(OH)D3 and iPTH distributions were normalized and the means fit with a sinusoidal function for both gender and latitudes: North >40, Central 32-40 and South <32 degrees. We analyzed PTH and total 25(OH)D separately in samples with detectable 25(OH)D2 (≥4 ng/mL). FINDINGS: Seasonal variation was observed for all genders and latitudes. 25(OH)D3 peaks occurred in September and troughs in March. iPTH levels showed an inverted pattern of peaks and troughs relative to 25(OH)D3, with a delay of 4 weeks. Vitamin D deficiency and insufficiency was common (33% <20 ng/mL; 60% <30 ng/mL) as was elevated iPTH levels (33%>65 pg/mL). The percentage of patients deficient in 25(OH)D3 seasonally varied from 21% to 48% and the percentage with elevated iPTH reciprocally varied from 28% to 38%. Patients with detectable 25(OH)D2 had higher PTH levels and 57% of the samples with a total 25(OH)D > 50 ng/mL had detectable 25(OH)D2. INTERPRETATION: 25(OH)D3 and iPTH levels vary in a sinusoidal pattern throughout the year, even in vitamin D2 treated patients; 25(OH)D3, being higher in the summer and lower in the winter months, with iPTH showing the reverse pattern. A large percentage of the tested population showed vitamin D deficiency and secondary hyperparathyroidism. These observations held across three latitudinal regions, both genders, multiple-years, and in the presence or absence of detectable 25(OH)D2, and thus are applicable for patient care.

Simultaneous measurement of thirteen steroid hormones in women with polycystic ovary syndrome and control women using liquid chromatography-tandem mass spectrometry.

BACKGROUND: The measurement of adrenal and ovarian androgens in women with PCOS has been difficult based on poor specificity and sensitivity of assays in the female range. METHODS: Women with PCOS (NIH criteria; n = 52) and control subjects with 25-35 day menstrual cycles, no evidence of hyperandrogenism and matched for BMI (n = 42) underwent morning blood sampling. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to simultaneously measure 13 steroids from a single blood sample to measure adrenal and ovarian steroids. Androgen and progesterone results were compared in the same samples using RIA. RESULTS: Testosterone, androstenedione, progesterone and 17OH progesterone levels were higher when measured using RIA compared to LC-MS/MS, although the testosterone RIA demonstrated the best agreement with the LC-MS/MS using a Bland-Altman analysis. Results using LC-MS/MS demonstrated that the concentration of androgens and their precursors were higher in women with PCOS than controls [median (2.5, 97.5th %ile); 1607 (638, 3085) vs. 1143 (511, 4784) ng/dL; p = 0.03]. Women with PCOS had higher testosterone [49 (16, 125) vs. 24 (10, 59) ng/dL], androstenedione [203 (98, 476) vs. 106 (69, 223) ng/dL] and 17OH progesterone levels [80 (17, 176) vs. 44 (17, 142) ng/dL] compared to controls (all P<0.02), but no differences in serum concentrations of the adrenal steroids DHEAS, cortisol, corticosterone and their 11 deoxy precursors. Women with PCOS also had an increase in the product:precursor ratio for 3ß-hydroxysteroid dehydrogenase [22% (6, 92) vs. 20% (4, 43); p = 0.009]. CONCLUSION: LC-MS/MS was superior to RIA in measuring androstenedione, progesterone and 17OH progesterone levels, while testosterone measurements were better matched in the two assays. Androgen levels were higher in women with PCOS in the absence of a difference in adrenal-predominant steroids. These data support previous findings that the ovary is an important source for the androgen excess in women with PCOS.

The measurement of 3-epimer 25-hydroxyvitamin D by mass spectrometry in clinical specimens detects inconsequential levels in adult subjects.

BACKGROUND: Vitamin D is derived from dietary sources or from the action of ultraviolet light on 7-dehydrocholesterol and undergoes a number of enzymatic modifications that lead to the synthesis of active vitamin D metabolites or metabolites with reduced biological activity. Among these, epimerization at the 3-hydroxyl group leads to the synthesis of 3-epimer 25-hydroxyvitamin D (3EVD). Described first in biological system experiments using in vitro incubation of vitamin D in cell culture, this molecule has been reported as having distinct activities when compared with 25-hydroxy vitamin D (25OHVD). Measurements of vitamin D have been conducted using a variety of methodologies and have led to conflicting assessments of the quantities of 3EVD3 that are measured. METHOD: The present article describes the development and use of a simple liquid chromatography-tandem mass spectrometry method validated by the Clinical Laboratory Improvement Amendments to quantitate 3EVD3 in 3528 subjects, including 309 children (162 are <2 years) and 232 pregnant women. RESULTS: Our findings demonstrate that, although 3EVD3 constitutes a significant proportion of measureable 25OHVD3 in subjects younger than 1 year, 3EVD3 levels are negligible in most subjects older than 1 year. CONCLUSIONS: It is important to choose the correct 25OHVD assay dependent on the age of the patient. Patients younger than 1 year should be run on a liquid chromatography-tandem mass spectrometry assay proven to not have potential contributions from any 3EVD present in the sample.

Specificity and predictive value of circulating testosterone assessed by tandem mass spectrometry for the diagnosis of polycystic ovary syndrome by the National Institutes of Health 1990 criteria.

OBJECTIVE: To determine whether liquid chromatography-tandem mass spectrometry (LC-MS/MS) determination of total (TT) and free (FT) testosterone is more specific than extraction chromatography-radioimmunoassay (RIA) for distinguishing women with polycystic ovary syndrome (PCOS) from controls and whether differing cutoff values should be used depending on the setting. DESIGN: Prospective case-control cohort study. SETTING: Tertiary care center and reference laboratory. INTERVENTION(S): Blood sampling. PATIENT(S): One hundred patients with PCOS and 100 controls. MAIN OUTCOME MEASURE(S): Circulating TT measured by RIA and LC-MS/MS and FT measured by equilibrium dialysis using RIA or LC-MS/MS-generated TT values. RESULT(S): T measurement by RIA and LC-MS/MS similarly differentiated patients with PCOS from controls; detection of PCOS was higher for FT for both methods. TT values demonstrated greater overlap between patients with PCOS and controls than did FT for both RIA (80% vs. 42% overlap) and LC-MS/MS (52% vs. 67% overlap). A lower cutoff value by LC-MS/MS was better suited for the study of patients seen in the clinical (referred) setting (35 and 4.0 ng/dL for TT and FT, respectively) than in the screening of a general population (50 and 5.0 ng/dL for TT and FT, respectively). CONCLUSION(S): Extraction chromatography-RIA and LC-MS/MS measurements of T have similar performance for differentiating patients with PCOS from healthy controls; LC-MS/MS may be preferable given its relative ease of automation. Compared with FT, measurement of TT has relatively limited value for distinguishing PCOS from normal. Finally, different cutoff values should be considered depending on the clinical/investigative setting, with higher values being used in the study of biased (e.g., clinical or referred) populations.

Quantitative insulin analysis using liquid chromatography-tandem mass spectrometry in a high-throughput clinical laboratory.

BACKGROUND: Circulating insulin concentrations reflect the amount of endogenous insulin produced by the pancreas and can be monitored to check for insulin resistance. Insulin is commonly measured using immunochemiluminometric assays (ICMA). Unfortunately, differing crossreactivities of the various ICMA antibodies have led to variability in assay results. In contrast, liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based approaches can provide a highly specific alternative to immunoassays. METHODS: Insulin was extracted from patient serum and reduced to liberate the insulin B chain. Subsequent resolution of the peptide was achieved by LC coupled to triple-quadrupole MS. Selected-reaction monitoring of B-chain transitions was used for quantification. Recombinant human insulin was used as a calibrator and was compared against the National Institute for Biological Standards and Control (NIBSC) reference standard. Bovine insulin and a stable isotopic-labeled ((13)C/(15)N) human insulin B chain were used and compared as internal standards. RESULTS: The LC-MS/MS assay described herein has been validated according to CLIA guidelines with a limit of detection of 1.8 µIU/mL (10.8 pmol/L) and a limit of quantitation of 3 µIU/mL (18.0 pmol/L). A correlation between the LC-MS/MS assay and a US Food and Drug Administration-approved ICMA was completed for patient samples and the resulting Deming regression revealed good agreement. A reference interval for the assay was established. CONCLUSIONS: A simple, high-throughput, quantitative LC-MS/MS insulin assay traceable to the NIBSC standard has been successfully developed and validated.

Serum concentrations of 1,25-dihydroxyvitamin D2 and 1,25-dihydroxyvitamin D3 in response to vitamin D2 and vitamin D3 supplementation.

OBJECTIVE: The purpose of this study was to determine 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and 1,25-dihydroxyvitamin D2 [1,25(OH)2D2] levels in healthy adults consuming 1000 IU vitamin D2 or vitamin D3 per day for 11 weeks. SUBJECTS AND DESIGN: Blood from 34 healthy male and female adults, aged 18 to 79 years, from a placebo-controlled, double-blind study who received a placebo, 1000 IU vitamin D3, or 1000 IU vitamin D2 daily for 11 weeks at end of winter was analyzed. Serum levels of 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, 1,25(OH)2D2, and 1,25(OH)2D3 were determined by liquid chromatography-tandem mass spectroscopy. RESULTS: Of the adults, 82% were vitamin D insufficient (serum 25-hydroxyvitamin D [25(OH)D <30 ng/mL]) at the start of the study. Administration of vitamin D2 and vitamin D3 induced similar increases in total 25(OH)D as well as in 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3, respectively. Compared with placebo and adjusting for baseline levels, 1000 IU daily of vitamin D2 was associated with a mean increase of 7.4 pg/mL (95% confidence interval, 4.4-10.3) in 1,25(OH)2D2, which was accompanied by a mean decrease of 9.9 pg/mL (-15.8 to -4.0) in 1,25(OH)2D3. No such differences accompanied administration of 1000 IU daily of vitamin D3. CONCLUSION: Vitamin D2 and vitamin D3 were effective in raising and maintaining total serum concentrations of 25(OH)D. Ingestion of vitamin D2 also resulted in an increase in serum concentrations of 1,25(OH)2D2. This increase was accompanied by a comparable decrease in serum concentrations of 1,25(OH)2D3; therefore, the total 1,25-dihydroxyvitamin D [1,25(OH)2D] concentrations did not significantly change after 11 weeks compared with baseline levels. Ingestion of vitamin D3 did not alter serum concentrations of 1,25(OH)2D3 or total 1,25(OH)2D. Therefore, ingestion of 1000 IU vitamin D2 or vitamin D3 for 11 weeks was effective in raising total serum concentrations of 25(OH)D as well as sustaining serum concentrations of total 1,25(OH)2D.

A novel mass spectrometry-based assay for the accurate measurement of thyroglobulin from patient samples containing antithyroglobulin autoantibodies.

Thyroid cancer is the most common endocrine cancer in the United States. The primary treatment of thyroid cancer is partial or complete thyroidectomy in patients in whom the cancer is discovered preoperatively, and is often followed by radioactive iodine ablation. After the initial therapy, patients are followed up regularly, most commonly by measurement of serum thyroglobulin (Tg) levels and high-resolution neck ultrasound. As Tg is only produced within the thyroid gland, it has long been recognized as an excellent biomarker for the presence of residual disease after treatment. A number of immunoassays are in common use to measure serum Tg levels. Unfortunately, irrespective of which method is chosen, there is a major potential artifact, in that the presence of autoantibodies binding to Tg (ATG) may bias the results to the point where they are clinically unreliable. This article describes a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the measurement of serum Tg after tryptic digestion of serum samples. The method is compared to Tg analyses using both a Food and Drug Administration-approved immunometric assay (IMA) and a well-respected, clinically used radioimmunoassay. In the absence of ATG, the new LC-MS/MS assay demonstrates equivalency compared to the IMA. However, in ATG-positive patients, the IMA Tg results are lower than the LC-MS/MS assay and the radioimmunoassay Tg results are typically higher. These studies demonstrate the accuracy and validity of the measurement of Tg by LC-MS/MS. This assay will permit the accurate determination of Tg levels even in patients with ATG.

Novel lipoprotein subfraction and size measurements in prediction of mortality in maintenance hemodialysis patients.

BACKGROUND AND OBJECTIVES: Conventional lipid profiles usually cannot predict cardiovascular outcomes in chronic disease states. We hypothesized that novel lipoprotein subfraction concentrations and LDL particle size measurements better predict mortality in maintenance hemodialysis (MHD) patients. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Mortality-predictability of LDL particle diameter and lipoprotein subfraction concentrations, measured by novel ion mobility, was examined in a cohort of 235 hemodialysis patients who were followed for up to 6 years using Cox models with adjustment for important covariables. RESULTS: Patients were 54 ± 14 years old (mean ± SD) and included 45% women with total, LDL and HDL cholesterol levels of 143 ± 42, 76 ± 29, and 37 ± 12 mg/dl, respectively. Over 6 years, 71 patients (31%) died. Conventional lipid profile was not associated with mortality. The death hazard ratio (HR, 95% confidence interval) of the highest versus lowest quartiles of very small and large LDL particle concentrations were 2.43 (1.03 to 5.72) and 0.38 (0.15 to 0.96), respectively. Across increasing quartiles of LDL particle diameter, death HRs were 1.00, 0.93 (0.46 to 1.87), 0.43 (0.21 to 0.89), and 0.45 (0.31 to 1.00), respectively. CONCLUSIONS: Whereas conventional lipid profile cannot predict mortality in MHD patients, larger novel LDL particle diameter or higher large LDL particle concentrations appear predictive of greater survival, whereas higher very small LDL particle concentration is associated with higher death risk. Examining lipoprotein subfraction modulation in chronic diseases is indicated.

Testosterone reference ranges in normally cycling healthy premenopausal women.

INTRODUCTION: At present, there are no well-accepted reference ranges for serum testosterone concentrations in women. AIM: The aim of this study was to determine the reference ranges for serum testosterone and sex hormone-binding globulin (SHBG) in premenopausal women with normal menstrual cycles. METHODS: We measured serum total, free, and bioavailable testosterone and SHBG concentrations in 161 healthy, normally cycling women (18-49 years). Morning blood samples were collected during follicular, mid-cycle, and luteal phases of the menstrual cycle and analyzed using validated methods. Mean, median, and weighted average hormone levels across menstrual cycle phases as well as percentiles for a typical 30-year-old woman were determined. MAIN OUTCOME MEASURES: Age-related serum levels of total, free, and bioavailable testosterone and SHBG levels in normally cycling premenopausal women. RESULTS: Serum testosterone concentrations exhibited an age-related decline, whereas SHBG remained relatively stable across studied age ranges. Reference ranges for total, free, and bioavailable testosterone and SHBG were established using 5th and 95th percentiles. The estimated 5th and 95th percentiles for a 30-year-old woman were: testosterone, 15-46 ng/dL (520-1595 pmol/L); free testosterone, 1.2-6.4 pg/mL (4.16-22.2 pmol/L); calculated free testosterone, 1.3-5.6 pg/mL (4.5-19.4 pmol/L); bioavailable testosterone, 1.12-7.62 ng/dL (38.8-264.21 pmol/L); and SHBG 18-86 nmol/L. The variations of hormones and SHBG across menstrual cycle were consistent with previous literature. CONCLUSIONS: Reference ranges for free, total, and bioavailable testosterone and SHBG were established in premenopausal women using validated immunoassays and an adequate number of subjects consistent with recommendations by the National Committee for Clinical Laboratory Standards. The increase in testosterone in the mid-cycle period is relatively small compared with the overall variability, so these reference ranges can be applied irrespective of the day in the menstrual cycle the sample has been taken.

Validation of a total testosterone assay using high-turbulence liquid chromatography tandem mass spectrometry: total and free testosterone reference ranges.

Accurate measurement of testosterone concentration is of critical importance when diagnosing and treating male hypogonadism, congenital adrenal hyperplasia, premature or delayed puberty, and androgen excess in polycystic ovary syndrome or other virilizing conditions. However, some assays have inherent limitations and biases that affect measurement of low-testosterone values. Therefore, we developed a highly specific online mass spectrometry method. Sera were extracted online using high-turbulence flow liquid chromatography coupled to analytical HPLC and atmospheric pressure chemical ionization tandem mass spectrometry (HTLC-APCI-MS/MS). Analyte ions were monitored by multiple reaction monitoring (MRM). Total analysis time was 1.15 min per sample when using the multiplexing system. Testosterone concentrations were measured directly from 150 microL of serum or plasma without derivatization or liquid-liquid extraction. The lower limit of quantification was 0.3 ng/dL, and the assay was linear up to 2000 ng/dL. The method compared very well with an established RIA: y=1.02x+1.5, r(2)=0.994. Comparison with a platform immunoassay confirmed the previously reported ICMA positive bias at low concentrations. Male and female adult and pediatric reference ranges were developed for this very sensitive and accurate high-throughput LC-MS/MS method. This method is suitable for measuring the expected low-testosterone concentrations seen in women, children, and hypogonadal males and for monitoring testosterone suppressive therapy in prostate cancer patients.

Ion mobility analysis of lipoprotein subfractions identifies three independent axes of cardiovascular risk.

OBJECTIVE: Whereas epidemiological studies show that levels of low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) predict incident cardiovascular disease (CVD), there is limited evidence relating lipoprotein subfractions and composite measures of subfractions to risk for CVD in prospective cohort studies. METHODS AND RESULTS: We tested whether combinations of lipoprotein subfractions independently predict CVD in a prospective cohort of 4594 initially healthy men and women (the Malmö Diet and Cancer Study, mean follow-up 12.2 years, 377 incident cardiovascular events). Plasma lipoproteins and lipoprotein subfractions were measured at baseline with a novel high-resolution ion mobility technique. Principal component analysis (PCA) of subfraction concentrations identified 3 major independent (ie, zero correlation) components of CVD risk, one representing LDL-associated risk, a second representing HDL-associated protection, and the third representing a pattern of decreased large HDL, increased small/medium LDL, and increased triglycerides. The last corresponds to the previously described "atherogenic lipoprotein phenotype." Several genes that may underlie this phenotype-CETP, LIPC, GALNT2, MLXIPL, APOA1/A5, LPL-are suggested by SNPs associated with the combination of small/medium LDL and large HDL. CONCLUSIONS: PCA on lipoprotein subfractions yielded three independent components of CVD risk. Genetic analyses suggest these components represent independent mechanistic pathways for development of CVD.

Direct determination of lipoprotein particle sizes and concentrations by ion mobility analysis.

BACKGROUND: Current methods for measuring the concentrations of lipoprotein particles and their distributions in particle subpopulations are not standardized. We describe here and validate a new gas-phase differential electrophoretic macromolecular mobility-based method (ion mobility, or IM) for direct quantification of lipoprotein particles, from small, dense HDL to large, buoyant, very-low-density lipoprotein (VLDL). METHODS: After an ultracentrifugation step to remove albumin, we determined the size and concentrations of lipoprotein particles in serum samples using IM. Scan time is 2 min and covers a particle range of 17.2-540.0 A. After scanning, data are pooled by totaling the particle number across a predetermined size range that corresponds to particular lipoprotein subclasses. IM results were correlated with those of standard methods for cholesterol and apolipoprotein analysis. RESULTS: Intra- and interassay coefficients of variation for LDL particle size were <1.0%. The intra- and interassay variation for LDL and HDL particle subfraction measurements was <20%. IM-measured non-HDL correlated well with apolipoprotein B (r = 0.92). CONCLUSIONS: The IM method provides accurate, reproducible, direct determination of size and concentration for a broad range of lipoprotein particles. Use of this methodology in studies of patients with cardiovascular disease and other pathologic states will permit testing of its clinical utility for risk assessment and management of these conditions.

A cross-sectional study of bone turnover markers in healthy premenopausal women.

BACKGROUND: Biochemical markers of bone turnover (BTMs) provide useful information in the diagnosis and management of metabolic bone diseases. Currently, there exist few published reference ranges for bone markers in healthy premenopausal women using the newer, automated assays of bone turnover. This cross-sectional study of healthy premenopausal women was performed to determine reference ranges for four different markers of bone turnover and to compare reference ranges in users and non-users of oral contraceptives (OCs). METHODS: Urinary N-telopeptide of type 1 collagen (NTX) was determined from fasting second morning-void urine of healthy premenopausal women. In addition, fasting serum was collected for determination of C-telopeptide of type I collagen (CTX), bone-specific alkaline phosphatase (bone ALP), and N-terminal propeptide of type 1 procollagen (PINP). Subjects underwent central dual energy X-ray absorptiometry and completed a questionnaire regarding medical history and activities known to affect bone health. RESULTS: Serum and urine samples were collected from 237 healthy premenopausal women (119 OC users and 118 non-users) between the ages of 28 and 45 years. The mean age of subjects was 37 years, with a mean bone mineral density T-score of -0.1 at the lumbar spine and 0.0 at the total hip. Logarithmic transformation produced normal distributions for all markers but NTX. Mid-95% ranges for each marker were generally consistent with those reported by manufacturers. For each BTM examined, values were skewed toward the lower end of the range. Median NTX levels for OC users and non-users were 16.0 and 29.0 nmol/mmol creatinine, respectively. The mid-95% ranges for NTX in OC users and non-users were 3-60 and 4-64 nmol/mmol creatinine, respectively. Median levels of CTX, bone ALP, and PINP were also lower in OC users than non-users. The mean level of each BTM was significantly lower in OC users than non-users (P<0.01), whereas reference ranges (geometric mean+/-2 SD) were somewhat similar for the two groups. CONCLUSION: Values obtained from this well-characterized population provide reference ranges for BTMs in healthy premenopausal women. Median and mean BTM levels for OC users were consistently lower compared with non-users; thus, separate reference ranges are required for these two groups of premenopausal women. The relevance of premenopausal reference ranges for postmenopausal women remains uncertain.

GH peak response to GHRH-arginine: relationship to insulin resistance and other cardiovascular risk factors in a population of adults aged 50-90.

OBJECTIVE: To assess the GH response to GHRH-arginine in apparently healthy adults in relation to cardiovascular risk factors. DESIGN: Cross-sectional. PATIENTS: Eighty-six male and female volunteers aged 50-90. MEASUREMENTS: GH peak response to GHRH-arginine and cardiovascular risk factors, including obesity, insulin resistance, low levels of high density lipoprotein (HDL) cholesterol, elevated triglycerides, and hypertension. The primary outcome measurement was GH response to GHRH-arginine. The relationship between GH peak responses and cardiovascular risk factors was determined after data collection. RESULTS: GH peaks were highly variable, ranging from 2.3 to 185 microg/l (14% with GH peaks < 9 microg/l). An increasing number of cardiovascular risk factors were associated with a lower mean GH peak (P < 0.0001). By univariate analysis, fasting glucose, insulin, body mass index (BMI), HDL cholesterol and triglycerides were significantly associated with GH peak (all P < 0.0001). Multiple regression analysis revealed that fasting glucose, fasting insulin, BMI, triglycerides and sex accounted for 54% of GH peak variability. The role of abdominal fat as it relates to GH peak was explored in a subset of 45 subjects. Trunk fat and abdominal subregion fat measured by dual energy X-ray absorptiometry (DXA) were inversely related to GH peak (P < 0.008 and 0.001, respectively). Analysis of this subgroup by multiple regression revealed that subregion abdominal fat became the significant obesity-related determinant of GH peak, but still lagged behind fasting insulin and glucose. CONCLUSIONS: GH response to secretagogues was highly variable in apparently healthy adults aged 50-90 years. Peak GH was significantly related to fasting glucose, insulin, BMI, HDL cholesterol, triglycerides, trunk fat and abdominal subregion fat, with fasting glucose ranking first by multiple regression analysis. There was a strong relationship between cardiovascular risk factors and low GH, with individual risk factors being additive. Although these data do not differentiate between low GH being a cause or an effect of these cardiovascular risk factors, they indicate that the relationship between low GH and increased cardiovascular risk may be physiologically important in the absence of pituitary disease.