Spectrophotometry of tissue thromboplastin in cerebrospinal fluid

We describe a two-stage method for measuring thromboplastin in cerebrospinal fluid, based on the amidolytic determination of the generation rate of Factor Xa. We investigated the effect of variations in the duration of incubation, and in pH, temperature, and concentrations of calcium, buffer, and prothrombin complex (source of Factors VII and X). Optimal assay conditions are specified. The detection limit is 6 units/L and the results indicate an upper limit of normal of 14 units/L. The coefficients of variation were 7.7% within-day and 9.2--16.0% day-to-day, depending on the concentration.