Clinical Lab Calculation Practice
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Several bedside calculations adjust or interpret lab values: corrected calcium for low albumin, corrected phenytoin for hypoalbuminemia (Sheiner-Tozer), the absolute neutrophil count, and the anion gap.
FormulasCorrected Ca = measured Ca + 0.8 × (4.0 − albumin)Corrected phenytoin = measured ÷ [(0.2 × albumin) + 0.1]ANC = WBC × (% segs + % bands) ÷ 100 • Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻)
Worked example
Measured calcium 7.5 mg/dL, albumin 2.5 g/dL. Corrected = 7.5 + 0.8 × (4.0 − 2.5) = 7.5 + 1.2 = 8.7 mg/dL.
💡 Only correct calcium when albumin is low. For phenytoin with CrCl < 10, the 0.2 factor becomes 0.1.