Should Plasma p - Endorphin Be Measured in Patients with Disorders of the Hypothalamic - Pituitary - Adrenal

CLINICAL CHEMISTRY, Vol. 32, No. 5, 1986 895 We prepared aqueous calcium standards in concentrations verified by atomic absorption, AMP buffer (3.5 mol/L, pH 10.7), AMP buffer with sodium acetate (25 g/L, pH 10.7), and start reagent(CPC, 0.48g/L;8-hydroxyquinoline, 5 g/L; pH 1.6). Manual and automated versions were performed by mixing sample, distilled water, AMP buffer, and start reagentin volume proportions of 1, 5.5, 28, and 4, respectively. Absorbances at 570 nm were read within 15 mm, subtracting values for reagent blanks. The aqueous standards gave sigmoid standard curves on the Cobas Bio. Deviations from the straight line passing through the 0 and 2.5 mmolJL points were -33, -24, -7,6, 13, and 13%;and -16, -15, -3, 1,2, and 1%for the 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 mmol/L standards in the presence and absence of acetate, respectively. Manual results were simi-