Patent ID: 8415162

Claim:
A method for determining an amount of a vitamin D metabolite in a test sample, the method comprising: (a) providing a set of calibrator samples, each calibrator sample comprising a different amount of a first isotopically-labeled standard in a biological matrix, (b) providing to each calibrator sample a selected constant amount of a second isotopically labeled standard, the first and second isotopically labeled standards having distinct isotope content, and wherein the first and second isotopically labeled standards are isotopically-labeled vitamin D metabolite derivatives; (c) subjecting the calibrator samples comprising the first and second isotopically-labeled standards to mass spectrometry to determine signal intensities corresponding to the first and second isotopically-labeled standards; (d) generating a calibration curve based on ratios of the determined signal intensities of the first and second isotopically-labeled standards as a function of the amount of the first isotopically-labeled standard in the calibrator samples; (e) contacting a test sample with the selected constant amount of the second isotopically-labeled standard; (f) subjecting the test sample comprising the second isotopically-labeled standard to mass spectrometry to determine signal intensities corresponding to the second isotopically labeled standard and the vitamin D metabolite, and (g) using the calibration curve and the determined signal intensities corresponding to the second isotopically labeled standard and the vitamin D metabolite to determine the amount of the vitamin D metabolite in the test sample.