Laboratory tests - urinalysis in rheumatic disease

Role

Urinalysis is a simple, essential screening test for renal involvement in systemic rheumatic disease, particularly SLE and vasculitis, where new proteinuria or haematuria can be the earliest detectable sign of active glomerulonephritis
Performed routinely at diagnosis and at regular intervals during follow-up in patients with SLE or other conditions carrying renal involvement risk, given how often early renal disease is otherwise asymptomatic

Active glomerulonephritis (lupus nephritis, ANCA-associated vasculitis) causes proteinuria and dysmorphic haematuria/red cell casts on urine microscopy before symptoms or a significant creatinine rise are necessarily apparent - urinalysis can therefore detect renal involvement at an earlier, more treatable stage than waiting for symptomatic or biochemical (creatinine-based) deterioration

Any new proteinuria or haematuria in a patient with SLE or vasculitis warrants formal quantification (urine protein:creatinine ratio) and urine microscopy for casts/dysmorphic cells, not just a repeat dipstick - a positive dipstick is a trigger for further characterisation, not a result to be dismissed or simply repeated
Red cell casts specifically indicate a glomerular source of haematuria (as opposed to a lower urinary tract cause) and are a strong supportive finding for active glomerulonephritis in the appropriate clinical context

New significant proteinuria/active urinary sediment in SLE or vasculitis should prompt urgent nephrology/rheumatology co-management and consideration of renal biopsy, given the time-sensitivity of treating active lupus nephritis or renal vasculitis
Regular urinalysis monitoring continues even in patients with quiescent disease, given the risk of a renal flare occurring without other obvious systemic symptoms

Lupus nephritis, ANCA-associated vasculitis, glomerulonephritis general workup, urine protein:creatinine ratio quantification

Urinalysis is one of the highest-yield, lowest-cost screening tests in rheumatic disease follow-up - a new abnormality here can be the first sign of a major, treatment-changing complication (active nephritis) well before other clinical or biochemical markers become abnormal

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