Synopsis
Translate kidney and liver assessment into an individual medicine plan, distinguishing stable impairment from acute deterioration and dose adjustment from treatment interruption.
- Use the renal measure required by the specific medicine: laboratory eGFR and Cockcroft–Gault creatinine clearance are not interchangeable for every dosing decision, particularly with DOACs.
- Check the age, current weight, creatinine value, units and clinical stability before accepting a calculated clearance. Creatinine-based estimates become unreliable during rapidly changing acute kidney injury.
- For stable renal function using creatinine in micromol/L, Cockcroft–Gault clearance in mL/min is (140 − age) × weight × 1.23 / creatinine for men, or × 1.04 for women; extremes of body composition need careful interpretation.
Reasoning priorities
Assess the degree and trajectory of renal impairment.
Use a result recent enough for the clinical situation. The creatinine lags behind a sudden change, so urine output and physiology can identify deterioration before a new steady state exists. Repeat testing should be timed to the risk and linked to a clear plan for handling doses while the trajectory remains uncertain.
Worked reasoning
A 79-year-old woman weighs 50 kg and has stable creatinine of 100 micromol/L; the laboratory eGFR is 51 mL/min/1.73 m². A proposed medicine requires Cockcroft–Gault clearance for dosing, and its supplied dose table changes below 40 mL/min.
- Confirm that creatinine is stable and the measured 50 kg weight is a reasonable input for this patient. Identify the required output as creatinine clearance in mL/min; the reported indexed eGFR cannot simply be copied into the product table.
- Calculate the age term: 140 − 79 = 61 years. Multiply 61 × 50 × 1.04 = 3,172, then divide by creatinine 100 micromol/L to obtain an estimated clearance of 31.72 mL/min.
- Compare 31.72 with the supplied 40 mL/min boundary and use the below-40 dosing category for the next product-specific decision. Do not invent a dose from the clearance alone: the exact agent, indication and complete dose table remain necessary.
- Independently check by estimating 61 × 50 is about 3,000 and division by about 100 should yield roughly 30, not 300. Record the inputs, method, result and final action to use the lower-clearance category, then verify the actual product regimen before signing.
A patient with a previously stable regimen develops dehydration and rising creatinine.