Phenytoin concentrations in venous versus capillary blood of geriatric patients.

In 15 elderly patients who had seizure disorders, venous blood (standard venipuncture) was compared with capillary blood (finger lancet puncture) as the source of the specimen for determination of serum phenytoin concentration. The values obtained by the two procedures were similar (r = 0.99). The mean serum phenytoin levels in the venous samples was 17.3 micrograms/ml, and in the capillary samples 17.0 micrograms/ml; the paired t test showed no statistical difference. Either method provides an adequate blood sample for determination of phenytoin, and both may be used interchangeably. Capillary samples may be preferable for aged patients in whom venipuncture proves difficult or painful.