Applies Winter-Tozer correction for hypoalbuminemia and renal dysfunction. Estimates albumin-adjusted total and free phenytoin levels with toxicity interpretation.
| Albumin (g/dL) | Measured (mcg/mL) | Adjusted — Normal Renal | Adjusted — CKD | Clinical Implication |
|---|---|---|---|---|
| 4.0 (normal) | 15 | 15.0 | 15.0 | No correction needed |
| 3.0 | 15 | 21.4 | 30.0 | True level higher than measured |
| 2.5 | 15 | 25.0 | 37.5 | Supratherapeutic despite normal-looking level |
| 2.0 | 15 | 30.0 | 50.0 | Potentially toxic — correction critical |
| 1.5 | 15 | 37.5 | 66.7 | Severely toxic — free level markedly elevated |
Normal Renal Function: Adjusted Level = Measured / [(0.2 x Albumin) + 0.1] Severe CKD (eGFR <20) or Dialysis: Adjusted Level = Measured / [(0.1 x Albumin) + 0.1] Estimated Free Level: Free = Adjusted Level x 0.1 Therapeutic Ranges: Total (adjusted): 10-20 mcg/mL Free: 1.0-2.0 mcg/mL Note: In normal renal function, phenytoin is ~90% protein-bound. In severe CKD, uremic toxins compete for albumin binding sites, reducing the denominator coefficient from 0.2 to 0.1.
