Causes of Acute Kidney Injury: Clinical Features, Typical Findings on Examination of the Urine and Confirmatory Tests
| Cause of AKI | Clinical features suggesting diagnosis | Typical urinalysis/urine microscopy | Confirmatory tests |
|---|---|---|---|
| Hypovolaemia/hypotension | Systolic BP <100 mmHg or a decrease in baseline BP of >40 mmHg or postural hypotension; low JVP | Normal urinalysis/hyaline casts | Resolution of AKI on correction of hypovolaemia/hypotension |
| Sepsis | Fever or reduced body temperature (<36°C) Clinical focus of infection | May be normal | Microbiological confirmation of infection |
| Nephrotoxic drugs and toxins | Exposure to known nephrotoxic drug or toxin (Table 25.2) | May be normal If there is acute tubular injury, epithelial cell casts and free renal tubular epithelial cells may be seen; eosinophiluria may be seen in drug-induced interstitial nephritis | Resolution of AKI on withdrawal of drug or toxin |
| Hepatorenal syndrome | Chronic or acute liver disease with liver failure and portal hypertension | Typically normal | Resolution of AKI with improvement in liver function |
| Diseases involving large renal vessels | |||
| Renal artery thrombosis/embolism/dissection | Flank pain | Mild proteinuria, haematuria | Renal artery duplex scan/CT |
| Renal vein thrombosis | Background of nephrotic syndrome | Proteinuria, haematuria | Renal vein duplex scan/CT |
| Diseases of small vessels and glomeruli | |||
| Glomerulonephritis/vasculitis | See Chapter 99 Evidence of multi-system disease | Proteinuria, haematuria | Renal biopsy |
| HUS/TTP | See Appendix 102.2 TTP may be associated with autoimmune disorders and with drugs | May be normal or mild proteinuria, haematuria | Renal biopsy |
| Severe hypertension with acute hypertensive nephrosclerosis | Severe hypertension, with retinal haemorrhages and exudates | Microscopic haematuria (75% of patients) or proteinuria | Renal biopsy |
| Scleroderma renal crisis(SRC) | Skin signs of scleroderma Moderate to severe hypertension, often with retinal haemorrhages and exudates | Proteinuria, if present, is usually mild The urine sediment is usually normal, with few cells or casts | Renal biopsy |
| Diseases of the tubulointerstitium | |||
| Allergic interstitial nephritis | Recent drug exposure Fever, rash and arthralgia | Proteinuria White cell casts or eosinophiluria | Renal biopsy |
| Acute bilateral pyelonephritis | Fever, flank pain, renal tenderness | Proteinuria Pyuria Bacteriuria | Urine microscopy and culture |
| Urinary tract obstruction | Abdominal or flank pain | May be normal | Ultrasonography Non-contrast CT |
AKI, acute kidney injury; CT, computed tomography; HUS/TTP, haemolytic uraemic syndrome/thrombocytopenic purpura; JVP, jugular venous pressure.