Urine Chemistry & Urinalysis

Check a 24-hour urine collection against expected creatinine excretion for sex and body weight, before a result from an incomplete collection is acted on.

Convert a spot urine protein-creatinine ratio into an estimated daily protein excretion, and know when the estimate breaks down.

Separate proximal from distal renal tubular acidosis by measuring how much filtered bicarbonate is lost — valid only during bicarbonate loading, once plasma bicarbonate has been normalised.

Estimate distal nephron potassium handling from paired urine and serum values — and understand why nephrologists increasingly avoid it.

Convert urine albumin between mg/L, mg/dL and µg/mL — the first step before an albumin-to-creatinine ratio, which is the number that actually carries meaning.

Grade albuminuria from a spot urine sample using the KDIGO A1–A3 categories, without needing a 24-hour collection.

Use urine electrolytes as a proxy for ammonium excretion, distinguishing gastrointestinal bicarbonate loss from renal tubular acidosis.

Convert urine creatinine between mg/dL, mmol/L, g/L and µmol/L — the denominator that makes a spot albumin or protein ratio usable without a timed collection.

Estimate urinary ammonium excretion from the difference between measured and calculated urine osmolality — the more robust alternative to the urine anion gap.

Estimate daily protein excretion from a spot urine sample, useful when non-albumin proteinuria is suspected.

Calculate the urine sodium to potassium ratio, used as a rough marker of mineralocorticoid effect and, on a timed collection, as a dietary surrogate — with descriptive bands rather than guideline thresholds.

Estimate urine osmolality from specific gravity using the last-two-digits rule, and know when the two measurements disagree.