Plasma catecholamine assays: calibration with spiked plasma versus aqueous solutions

Area of Science:

• Clinical Chemistry
• Analytical Biochemistry
• Pharmacology

Background:

• Plasma constituent assays commonly use both aqueous standards and spiked plasma.
• Previous high-performance liquid chromatographic (HPLC) assays using spiked plasma for norepinephrine, epinephrine, and dopamine showed lower detection thresholds, indicating higher concentrations.
• This suggests potential interference or binding of spiked catecholamines during the assay process.

Purpose of the Study:

• To investigate the hypothesis that spiked catecholamines bind to plasma proteins, affecting extraction efficiency prior to HPLC.
• To compare the recovery of catecholamine standards in human albumin solution versus aqueous standards.
• To determine the optimal calibration method for accurate free catecholamine assays in plasma.

Main Methods:

• Comparison of catecholamine recovery rates using standards dissolved in human albumin solution.
• Comparative analysis with recovery rates using aqueous standards.
• High-performance liquid chromatography (HPLC) was employed for the analysis of catecholamines.

Main Results:

• Albumin was identified as a significant factor contributing to the reduced recovery of catecholamines.
• The binding of catecholamines to albumin interferes with their extraction process.
• Extraction of aqueous standards demonstrated a more reliable calibration method compared to using spiked plasma.

Conclusions:

• Albumin in plasma significantly impacts the recovery of spiked catecholamines, leading to inaccurate assay results.
• Calibration using aqueous standards is superior to using spiked plasma for accurate free catecholamine measurements.
• This study highlights the importance of considering protein binding in the development and validation of bioanalytical methods for catecholamines.