An equation for calculating phenytoin levels in patients with low albumin levels in “Pitfalls & pearls for 8 common lab tests” (J Fam Pract. 2014;63:198-205) was incorrect. The equation, known as the Sheiner-Tozer equation, should have read: phenytoin concentration adjusted = concentration reported/([adjustment × serum albumin] + 0.1), where adjustment = 0.2 for creatinine clearance ≥20, or adjustment = 0.1 for creatinine clearance <20. This equation has been corrected in the online edition of the article.

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