BACKGROUND:Measurement of serum androgens is important in adult, geriatric, pediatric endocrinology, and oncology patients. We developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for simultaneous measurement of androstenedione, dehydroepiandrosterone (DHEA), and testosterone in these patients.

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High-sensitivity measurement of serum estrogens is important in adult and pediatric endocrinology and oncology. We developed a high-sensitivity liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for simultaneous measurement of estrone (E1) and estradiol (E2). Aliquots of 200 muL of serum were spiked with internal standard, extracted, derivatized with dansyl chloride, and analyzed by LC-MS/MS using 2-dimensional chromatographic separation. Total imprecision for the method was less than 11%; the limit of quantitation was 1 pg/mL. Reference intervals were established with samples from more than 900 healthy postmenopausal women, men, girls, and boys. Concentrations of estrogens in children reached adult levels by Tanner stage 3. In men and postmenopausal women, the median concentrations of total estrogens (E1 + E2) were 39 and 22 pg/mL, and the median E2/E1 ratios were 0.98 and 0.55, respectively. The method requires a small sample volume and has adequate sensitivity and specificity for analyzing estrogens in samples from postmenopausal women, men, and children.

BACKGROUND For many years, basic and clinical researchers have taken advantage of the analytical sensitivity and specificity afforded by mass spectrometry in the measurement of proteins. Clinical laboratories are now beginning to deploy these work flows as well. For assays that use proteolysis to generate peptides for protein quantification and characterization, synthetic stable isotope–labeled internal standard peptides are of central importance. No general recommendations are currently available surrounding the use of peptides in protein mass spectrometric assays. CONTENT The Clinical Proteomic Tumor Analysis Consortium of the National Cancer Institute has collaborated with clinical laboratorians, peptide manufacturers, metrologists, representatives of the pharmaceutical industry, and other professionals to develop a consensus set of recommendations for peptide procurement, characterization, storage, and handling, as well as approaches to the interpretation of the data generated by mass spectrometric protein assays. Additionally, the importance of carefully characterized reference materials—in particular, peptide standards for the improved concordance of amino acid analysis methods across the industry—is highlighted. The alignment of practices around the use of peptides and the transparency of sample preparation protocols should allow for the harmonization of peptide and protein quantification in research and clinical care.

In community-dwelling men older than 60 years, serum testosterone is independently associated with the risk of osteoporotic fracture and its measurement may provide additional clinical information for the assessment of fracture risk in elderly men.

The noncovalent tetrameric association of the protein streptavidin formed by electrospray ionization (ESI) mass spectrometry has been observed intact and dissociated in the gas phase. An extended mass-to-charge ratio range quadrupole mass spectrometer was employed to examine the effects of harsher conditions in the ESI atmosphere-vacuum interface region on the streptavidin tetramer. Thermally induced dissociation caused the mass spectra to exhibit a series of complementary monomer and trimer ions that correspond to decomposition of the tetrameric species. Similar results were obtained with tandem mass spectrometric experiments on a Fourier transform ion cyclotron resonance mass spectrometer by application of sustained off-resonance irradiation (SORI) on a selected tetrameric charge state. The technique of single-frequency quadrupole excitation was used to accomplish selected-ion accumulation of the 14 + charge state of the tetramer during ion injection. Subsequent low energy SORI combined with broadband quadrupole cooling produced the 7 + monomer and 7 + trimer species, as well as the 6 + monomer and 8 + trimer complementary ions. The observed asymmetric breakup of the tetramer is qualitatively explained by using physical models.

Background:The standard screening test for vitamin B 12 deficiency, measurement of total plasma vitamin B 12 , has limitations of sensitivity and specificity. Plasma vitamin B 12 bound to transcobalamin (holoTC) is the fraction of total vitamin B 12 available for tissue uptake and therefore has been proposed as a potentially useful alternative indicator of vitamin B 12 status. Methods: We compared the diagnostic accuracy of total vitamin B 12 , holoTC, and a combination of both measures to screen for metabolic vitamin B 12 deficiency in an elderly cohort (age >60 years). Plasma methylmalonic acid and homocysteine were used as indicators of vitamin B 12 deficiency. Results: Low total vitamin B 12 (<148 pmol/L) and low holoTC (<35 pmol/L) were observed in 6.5% and 8.0%, and increased methylmalonic acid (>350 nmol/L) and homocysteine (>13 mol/L) were observed in 12.1% and 17.0% of the study participants. In multiple regression models, holoTC explained 5%-6% more of the observed variance in methylmalonic acid and homocysteine than did total vitamin B 12 (P <0.004). ROC curve analysis indicated that total vitamin B 12 and holoTC were essentially equivalent in their ability to discriminate persons with and without vitamin B 12 deficiency. Individuals

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