Inflammation in the concentrating tissue of the kidney can produce a range of manifestations:
- Haematuria (microscopic, ie on dipstick/microscopy only, or frank macroscopic)
- Nephrotic syndrome
- Acute nephritis
Protein in urine is not usually symptomatic in itself, the urine may seem more frothy. It would not be until the loss of a substantial amount of protein leads to hypoalbuminaemia and oedema (nephrotic syndrome) that it would be apparent.
Accompanying symptoms will tend to guide you to a diagnosis eg purpuric rash (HSP), photodermatitis and/or arhtritis (SLE), heavy proteinuria without haematuria (minimal change glomerulonephropathy).
Dipstick testing is sensitive for proteinuria and haematuria, but urine protein/albumin:creatinine ratio is more reliable. On microscopy, red and white cell casts are pathognomic. Presence of red cells useful to exclude other causes of apparent haematuria.
Complement – some characteristic patterns.
- Low C3, normal C4 = post streptococcal acute glomerulonephritis (PSAGN) or some kinds membproliferative GN.
- Low C3, C4 – SLE, membranous GN
If isolated low C3, and fits with PSAGN, diagnosis is clear. But check it normalizes in 3/12, else biopsy.
Biopsy – for definitive diagnosis. Although some conditions have patchy changes so sampling error possible.