title: Free cortisol in serum assayed by temperature-controlled ultrafiltration before fluorescence polarization immunoassay.
abstract: A method is described for a temperature-controlled ultrafiltration procedure to measure free cortisol in serum. A special thermometer with a sensor was developed, measuring the temperature directly in the ultrafiltration device. The sensor is screwed on the axis of the centrifuge rotor, and the centrifuge is placed in a temperature-controlled box so that the temperature of the sample is kept at 37 degrees C +/- 0.1 degrees C. The overall CV of the free cortisol assay ranges from 2.2% to 11.4%, of which the ultrafiltration contributes only 2.2-3.6%. Increasing amounts of cortisol-binding protein, as found in women using estrogen-containing oral contraceptives, have minor but significant effects on the free cortisol concentrations in serum. Serum free cortisol concentrations in a reference population (n = 114; central 95 percentiles) were 12-43 nmol/L (4-9.5% of total cortisol); in the group of the oral-contraceptive users (n = 27), the reference interval was 11-53 nmol/L (1.5-4.5%).
authors.affiliation: Department of Clinical Chemistry, University Hospital Leiden, The Netherlands.
authors.forename: E G
authors.initials: EG
authors.lastname: Lentjes
authors.forename: F
authors.initials: F
authors.lastname: Romijn
authors.forename: R J
authors.initials: RJ
authors.lastname: Maassen
authors.forename: L
authors.initials: L
authors.lastname: de Graaf
authors.forename: P
authors.initials: P
authors.lastname: Gautier
authors.forename: A J
authors.initials: AJ
authors.lastname: Moolenaar
mesh_terms: D001793:Blood Preservation; D004355:Drug Stability; D005260:Female; D016231:Fluorescence Polarization Immunoassay / Q000706:statistics & numerical data; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D006863:Hydrogen-Ion Concentration; D008297:Male; D012016:Reference Values; D012044:Regression Analysis; D015203:Reproducibility of Results; D013696:Temperature; D013997:Time Factors; D014462:Ultrafiltration
chemical_list: D006854:Hydrocortisone