Phenytoin test offered by Thyrocare aids in monitoring blood Phenytoin concentration and determine if the drug level is within the therapeutic range. Individuals are advised to take up the Phenytoin test every few days after starting phenytoin medication. Routine monitoring of serum phenytoin concentrations is necessary to maintain therapeutic efficacy and avoid toxicity. Phenytoin test may also aid in determining renal failure. Results should often be evaluated in conjunction with the time of blood collection, dosage, and other medical histories.