Renal Function & eGFR

Calculate the BUN:creatinine ratio, a quick pointer toward pre-renal, renal or other causes of an abnormal kidney profile.

Place an eGFR into its KDIGO G1–G5 category, and see why a normal-range result is not, by itself, a diagnosis of chronic kidney disease.

Estimate GFR from creatinine, age and sex using the 2021 race-free CKD-EPI equation, the current standard for adults.

The most accurate routine estimate of GFR, combining creatinine and cystatin C in the 2021 race-free equation.

Estimate GFR from cystatin C alone, independent of muscle mass — useful when creatinine cannot be trusted.

Estimate creatinine clearance in mL/min — the equation most drug labels specify for renal dose adjustment.

Convert serum creatinine between mg/dL and µmol/L, with adult reference ranges and what a change actually means.

Convert cystatin C between mg/L, µg/mL and nmol/L, with reference ranges and when to prefer it over creatinine.

Convert an indexed eGFR (mL/min/1.73 m²) to an absolute clearance in mL/min for drug dosing.

Identify renal magnesium wasting as the cause of hypomagnesaemia, correcting for the fraction of serum magnesium that is protein-bound and never filtered.

Identify renal phosphate wasting as the cause of hypophosphataemia, where the expected response is near-complete tubular conservation.

In hypokalaemia, separate extrarenal potassium loss from inappropriate renal potassium wasting.

Distinguish a pre-renal pattern from intrinsic renal injury by comparing sodium clearance with creatinine clearance — only valid before diuretics have been given.

Distinguish pre-renal from intrinsic renal injury when diuretics have already been given, using urea instead of sodium clearance.

Help separate SIADH from volume depletion in hyponatraemia — a raised FEUA persists in SIADH even after the sodium is corrected.

Stage acute kidney injury from a creatinine pair and urine output using the KDIGO criteria, taking whichever of the two gives the higher stage.

Classify a urine albumin-creatinine ratio into the KDIGO A1–A3 categories and see how it sharpens cardiovascular and renal risk at any eGFR.

Calculate delivered Kt/V with the Daugirdas second-generation single-pool formula, the standard measure of haemodialysis adequacy.

The legacy MDRD Study equation, still quoted in older records, drug labels and trial criteria.

Calculate creatinine clearance from a timed 24-hour urine collection and a paired serum creatinine.

Calculate the renal failure index from urine and plasma values to help distinguish a pre-renal from an intrinsic pattern of acute kidney injury.

Estimate GFR in children from height and creatinine using the bedside Schwartz equation.

Convert between BUN in mg/dL, urea in mg/dL and urea in mmol/L — three ways of reporting the same molecule.

Calculate the urea reduction ratio, the simplest bedside measure of dialysis adequacy, from pre- and post-dialysis BUN.

Calculate urine output in mL/kg/hr and apply the KDIGO thresholds used to define acute kidney injury.

Divide urine osmolality by serum osmolality to gauge whether the kidney is concentrating urine appropriately, and how early that ability tends to fail.