Albumin-Corrected Calcium (Payne) & Corrected Phenytoin (Sheiner-Tozer) Calculator
Calculates albumin-corrected total serum calcium (mg/dL) and albumin-corrected phenytoin concentration (mcg/mL) in hypoalbuminaemia.
⚠️ Educational Calculation & Clinical Safety Safeguard: In CrCl < 10 mL/min (uraemia), replace 0.2 with 0.1 in the Sheiner-Tozer denominator: C_corr = C_measured / [(0.1 × Albumin) + 0.1]. Educational calculations do not replace clinician assessment, patient-specific laboratory monitoring, or institutional prescribing protocols.
Interactive Calculator
Allowed physiological/compounding range: 4.0 to 18.0 mg/dL
Allowed physiological/compounding range: 1.0 to 6.0 g/dL
Allowed physiological/compounding range: 1.0 to 50.0 mcg/mL
Calculated Output (mg/dL (Ca) & mcg/mL (Phenytoin))
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Step-by-Step Mathematical Derivation & Explanation:
Validated Formula & Conversion Rules
Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin); Corrected Phenytoin (normal renal) = Measured Phenytoin / [(0.2 × Albumin) + 0.1]Worked Clinical Example
Albumin 2.5 g/dL, Measured Ca 7.8 mg/dL, Measured Phenytoin 8.0 mcg/mL: Corrected Ca = 7.8 + 0.8×(1.5) = 9.0 mg/dL; Corrected Phenytoin = 8.0 / (0.5 + 0.1) = 13.33 mcg/mL (within 10–20 mcg/mL therapeutic range).
Rounding Rules, Clinical Interpretation, Assumptions & Known Limitations
- 1. Purpose: Calculates albumin-corrected total serum calcium (mg/dL) and albumin-corrected phenytoin concentration (mcg/mL) in hypoalbuminaemia.
- 2. Required Inputs & Validated Units: Measured Total Serum Calcium (mg/dL, range 4.0–18.0), Serum Albumin (g/dL, range 1.0–6.0), Measured Total Phenytoin (mcg/mL, range 1.0–50.0)
- 3. Output Unit:
mg/dL (Ca) & mcg/mL (Phenytoin) - 4. Result Interpretation Notes: Computes Payne albumin-corrected total serum calcium (mg/dL) and Sheiner-Tozer albumin-corrected phenytoin (mcg/mL, including uraemic CrCl < 10 mL/min adjustment).
- 5. Rounding Guidance: Round Corrected Ca and Corrected Phenytoin to 1 or 2 decimal places.
- 6. Mathematical & Clinical Assumptions: Accounts for reduced protein binding in hypoalbuminaemia (serum albumin < 4.0 g/dL).
- 7. Known Limitations & Contraindications to Formula Use: In critically ill ICU patients or severe acid-base disturbances, direct ionised calcium and free (unbound) phenytoin assays are preferred over mathematical correction.
- 8. Supporting Compendial & Clinical References: Indian Pharmacopoeia (IP 2022), National Formulary of India (NFI), British National Formulary (BNF), and NCBI Bookshelf Clinical Pharmacology Compendia.