Core Laboratory

5. Cortisol

The procedure is a solid-phase radioimmunoassay, wherein 125I-labeled cortisol competes for a fixed time with cortisol in the sample for antibody sites. Because the antibody is immobilized to the wall of a polypropylene tube, simply decanting the supernatant suffices to terminate the competition and to isolate the antibody-bound fraction of the radiolabeled cortisol. Counting the tube in a gamma counter then yields a value, which represents by way of calibration curve to a measure of the cortisol present in the sample.

References:

  1. Foster L, Dunn R. Single-antibody technique for radioimmunoassay of cortisol in unextracted serum or plasma. Clin Chem 20:365-368, 1974.
  2. Farmer R, Pierce C. Plasma cortisol determination: radioimmunoassay and competitive protein binding compared. Clin Chem 20:411-414, 1974.
  3. Ruder H, et al. A radioimmunoassay for cortisol in plasma and urine. J Clin Endo Metab 35:219, 1972.

Interassay Coefficient of Variation (CV):

Sample 1 = 5.2% (n=20, mean=91.05, sd=4.69)
Sample 2 = 4.0% (n=20, mean=579.39, sd=22.90)
Sample 3 = 6.4% (n=20, mean=993.24, sd=63.46)

Detection Limit:

28 nmol/L

 

For more information, please contact the Core Laboratory manager or director.