Reproducibility of plasma catecholamine metabolites in normal subjects

Background: Plasma homovanillic acid (HVA) and methoxy-hydroxy-phenylglycol (MHPG) are often used in repeated measurement designs to assess dopamine and norepinephrine metabolism in clinical research. However, only limited data on the reproducibility of these metabolites are currently available. Methods: Plasma HVA and MHPG were measured in normal volunteers on five nonconsecutive mornings under fasting conditions and restricted smoking and physical activity. Results: Intraclass correlation coefficients (ICC) for plasma HVA and MHPG across 5 days were determined to be 0.85 and 0.79, respectively. ICC improved to 0.90 for HVA and 0.91 for MHPG when the average of the first 2 days was examined against the average of the last 2 days. Conclusions: Results suggested that under controlled conditions plasma HVA and MHPG measurements have good reproducibility.