Rapid, specific assay for plasma cortisol by competitive protein binding.

Area of Science:

• Biochemistry
• Endocrinology
• Analytical Chemistry

Background:

• Accurate measurement of plasma cortisol is crucial for diagnosing adrenal disorders.
• Existing competitive protein-binding assays (CPBAs) for cortisol may lack optimal specificity and precision.
• Radioimmunoassay (RIA) methods offer high specificity but can be complex.

Purpose of the Study:

• To develop and validate a modified competitive protein-binding assay (CPBA) for plasma cortisol.
• To enhance the specificity and precision of cortisol measurements.
• To compare the modified CPBA with existing methods, including RIA.

Main Methods:

• Plasma samples were deproteinized using an ethanol/phosphate buffer and heated.
• Horse serum was utilized as the source of transcortin.
• Separation of free radioactivity from protein-bound cortisol was achieved via liquid scintillation counting.

Main Results:

• The modified CPBA demonstrated improved specificity and precision over a standard CPBA using ethanol extraction and Florisil.
• Results obtained from the modified assay showed good correlation with a specific radioimmunoassay method.
• The assay procedure, including separation, was completed within 60 minutes.

Conclusions:

• The modified competitive protein-binding assay provides a reliable and efficient method for plasma cortisol determination.
• This assay offers advantages in specificity and precision, making it a valuable alternative to existing methods.
• The method's good correlation with RIA supports its clinical utility for cortisol analysis.