Substance P: Correlation of CSF and Plasma Levels

OBJECTIVE: To determine the correlation between cerebrospinal fluid and plasma concentrations of substance P. PATIENTS: 37 patients undergoing lumbar puncture for various diagnostic purposes. MEASUREMENTS: Samples of cerebrospinal fluid and blood were obtained at the same visit. Substance P was measured by radioimmunoassay technique. At least 4 separate measurements were conducted on each sample to insure accuracy. RESULTS: The mean plasma SP level was 1.195 (+/- 1.1). The mean cerebrospinal fluid substance P level was 1.075 (+/- .07). There was a statistically significant positive correlation between substance P level in the plasma and cerebrospinal fluid. The Pearson correlation coefficient was 0.656 (P < .0001) and the Spearman correlation coefficient was 0.698 (P < .0001). CONCLUSIONS: Plasma substance P levels closely correlate with cerebrospinal fluid substance P levels. This will simplify the measurement of substance P in the evaluation of therapeutic agents for headache.