Cortisol directly determined in serum by fluoroimmunoassay with magnetizable solid phase.

Area of Science:

• Biochemistry
• Immunochemistry
• Analytical Chemistry

Background:

• Accurate measurement of serum cortisol is crucial for diagnosing adrenal disorders.
• Established methods like radioimmunoassay have limitations, necessitating development of alternative assays.

Purpose of the Study:

• To develop and validate a direct fluoroimmunoassay for quantifying serum cortisol.
• To assess the assay's sensitivity, specificity, reliability, and correlation with radioimmunoassay.

Main Methods:

• Developed a direct fluoroimmunoassay using fluorescein-labeled cortisol and antibody-coupled magnetic particles.
• Employed sodium salicylate as a blocking agent to prevent interference from endogenous binding proteins.
• Utilized magnetic sedimentation for efficient separation, washing, and elution steps.

Main Results:

• The assay demonstrated high sensitivity, specificity, and reliability for routine use.
• Achieved acceptable correlation (r = 0.92) with a radioimmunoassay.
• Exhibited good precision (CV 4-10%) and analytical recovery (91-109%).

Conclusions:

• The direct fluoroimmunoassay is a viable and effective method for serum cortisol determination.
• This assay offers a practical alternative to radioimmunoassays for clinical laboratories.
• The use of magnetic separation enhances assay efficiency and throughput.