Plasma 21-deoxycortisol: comparison of a time-resolved fluoroimmunoassay using a biotinylated tracer with a radioimmunossay using (125)iodine

J Steroid Biochem Mol Biol. 2000 Jan-Feb;72(1-2):55-60. doi: 10.1016/s0960-0760(99)00151-x.


Plasma 21-deoxycortisol (21DF) is an excellent marker of 21-hydroxylase deficiency. Currently, it is the only marker able to detect heterozygous carriers with 21-hydroxylase deficiency after ACTH stimulation. We have already developed radioimmunoassays for 21DF using first tritiated, then 125I-21DF which had a ten-fold higher sensitivity. However, because the lifespan of 125I-21DF is short, the tracer needs to be reprepared every two months and this multiplies the risk of contamination by radioactive 125I vapours. We therefore developed a non-isotopic 21DF assay that uses a 21DF-biotin conjugate with a original bridge, a diaminopropyl arm, linking the steroid to biotin. The 21DF-biotin conjugate was measured by time-resolved fluorescence after adding streptavidin-europium to the microtitration wells. The analytical qualities of this assay were very similar to those of the radioimmunoassay using 125I-21DF as tracer. The results obtained by the two methods, in either normal subjects or patients with 21-hydroxylase deficiency, were virtually the same.

Publication types

  • Comparative Study

MeSH terms

  • Adrenal Hyperplasia, Congenital*
  • Adult
  • Age of Onset
  • Biotinylation
  • Calibration
  • Cortodoxone / blood*
  • Cortodoxone / immunology
  • Cross Reactions / immunology
  • Cross-Linking Reagents
  • Europium / metabolism
  • Female
  • Fluorescence
  • Fluoroimmunoassay / methods*
  • Humans
  • Immune Sera / immunology
  • Iodine Radioisotopes
  • Male
  • Menstrual Cycle
  • Radioimmunoassay / methods*
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Streptavidin / metabolism
  • Time Factors


  • Cross-Linking Reagents
  • Immune Sera
  • Iodine Radioisotopes
  • Europium
  • 21-deoxycortisol
  • Streptavidin
  • Cortodoxone