Investigations in Renal Disease

Urinalysis

•    Dipstick Testing

o    Rapid bedside screening tool; detects:

    Blood: may be haematuria, haemoglobinuria, or myoglobinuria

    Protein: suggests glomerular disease if persistent

    Nitrites: produced by Gram-negative bacteria (e.g. E. coli)

    Leukocyte esterase: indicates pyuria

    Glucose: glycosuria may indicate diabetes or proximal tubular dysfunction (Fanconi syndrome)

•    Microscopy

o    Red cell casts: pathognomonic for glomerulonephritis

o    White cell casts: seen in interstitial nephritis or pyelonephritis

o    Granular ("muddy brown") casts: typical of acute tubular necrosis (ATN)

o    Eosinophils in urine: suggest acute interstitial nephritis (AIN)

o    Crystals: uric acid, calcium oxalate, cystine may indicate stone risk or metabolic disorder

Proteinuria

•    Quantification

o    Use Albumin-to-Creatinine Ratio (ACR) or Protein-to-Creatinine Ratio (PCR) on early morning urine sample

    ACR >3 mg/mmol = microalbuminuria

    ACR >30 mg/mmol = significant albuminuria

    PCR >45 mg/mmol = heavy proteinuria

o    Persistent proteinuria is a hallmark of CKD, especially in diabetic nephropathy or glomerular disease

•    Nephrotic-range proteinuria: >300 mg/mmol (or >3.5 g/day)

Imaging

•    Renal Ultrasound (USS)

o    First-line investigation in renal disease

o    Assesses:

    Kidney size (small = chronic damage)

    Obstruction (hydronephrosis)

    Parenchymal echogenicity

    Cysts or masses

o    Small, shrunken kidneys → chronic kidney disease (CKD)

o    Enlarged kidneys → diabetic nephropathy, amyloidosis, HIV nephropathy, infiltrative disease

•    CT KUB (non-contrast)

o    Gold standard for renal/ureteric stones

o    Detects calcifications, haemorrhage, trauma

•    MRI/MRA

o    Used for vascular assessment (e.g. renal artery stenosis)

o    Contrast-enhanced MRI may assess tumours or complex cysts (note: gadolinium risk in advanced CKD)

Renal Biopsy

•    Indications

o    Unexplained AKI

o    Nephrotic/nephritic syndrome

o    Persistent proteinuria or haematuria

o    Suspected systemic disease with renal involvement (e.g. lupus nephritis, vasculitis)

o    Transplant dysfunction

•    Contraindications

o    Uncontrolled hypertension

o    Coagulopathy or thrombocytopenia

o    Active infection

•    Histology can identify:

o    Glomerulonephritis types (e.g. minimal change, membranous)

o    Tubulointerstitial nephritis

o    Amyloid, immune complex deposition, vasculitis patterns