NephrologyTier 2Topic

Laboratory tests - urinalysis in kidney disease

What it includes

Combines dipstick testing (protein, blood, leucocytes, nitrites, glucose, ketones, pH, specific gravity) with microscopy (cells, casts, crystals) - the first-line, rapid test in essentially every renal presentation
Foundational, low-cost screening test performed before any more invasive renal investigation

Findings and significance

Finding	Significance
Proteinuria	Glomerular disease if significant; transient/orthostatic proteinuria is benign
Dysmorphic RBCs, RBC casts	Glomerular haematuria
White cell casts	Pyelonephritis or interstitial nephritis
Granular/muddy brown casts	Acute tubular necrosis
Eosinophiluria	Acute interstitial nephritis (classically drug-induced)
Crystals (calcium oxalate, uric acid, cystine)	Stone disease; specific crystal types can suggest the stone type

Pitfalls

Dipstick protein does not detect Bence Jones protein (light chains) - a key trap in suspected myeloma - requires urine protein electrophoresis/free light chains specifically
Nitrites/leucocyte esterase support (but do not confirm) UTI - culture remains the reference standard

Acting on the result

Significant proteinuria on dipstick -> quantify with urine albumin:creatinine ratio (ACR) or protein:creatinine ratio (PCR)
Active urinary sediment (dysmorphic RBCs, casts) + reduced eGFR -> urgent nephrology referral, consider biopsy

Associations

Glomerulonephritis, acute tubular necrosis, acute interstitial nephritis, urinary tract infection, multiple myeloma (cast nephropathy)

Serial use

Urinalysis is repeated serially to monitor known renal disease activity and treatment response, not just for initial diagnosis

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