Published on 24/06/2015 by admin

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Last modified 24/06/2015

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Acute renal failure is a comorbidity that can be encountered in the long case setting. It can also be incidentally encountered when an electrolyte profile with renal function indices is given to the candidate by an examiner during the discussion. In such situations it is important that the candidate correctly interpret the results and take charge of the discussion.

Case vignette

An 81-year-old man is admitted after an episode of syncope. On arrival in hospital his pulse rate is 30 bpm and blood pressure is 80/50 mmHg. He has a background history of paroxysmal atrial fibrillation, which has been managed with digoxin, and hypertension, managed with enalapril. He has been recently commenced on a non-steroidal antiinflammatory drug for painful arthritis of the knees. Investigations reveal his creatinine level to be 247 μmol/L and urea 26 mmol/L. His serum potassium level is 6.5 mmol/L. ECG reveals sinus bradycardia with tall tented T waves.

Approach to the patient



In addition to serum biochemistry, the following investigations would be helpful:

1. Full blood count—looking for anaemia (may suggest chronicity), leucocytosis (may suggest sepsis or inflammation) and thrombocytopenia (possibly lupus nephritis).

2. Erythrocyte sedimentation rate—if elevated, can suggest multiple myeloma, connective tissue disease or vasculitis.

3. Urine analysis and midstream urine—for microscopy, culture and sensitivities. The presence of red cell casts and dysmorphic red cells in the phase-contrast microscopy would suggest glomerulonephritis; hyaline casts are non-specific; white blood cell casts suggest tubulointerstitial disease.

6. Renal arterial Doppler study—looking for evidence of renal artery stenosis. The renal vascular resistive index should also be checked. This gives an assessment of the renal microvascular resistance and hence intrarenal vascular disease.

7. According to the clinical indication, the following tests can also be requested: serum electrophoresis, immunoelectrophoresis, antinuclear antibody test (ANA), extractable nuclear antibody tests (ENA), antineutrophil cytoplasmic antibody tests (ANCAs), serum complement levels, streptococcal serology (antistreptolysin-O test (ASOT) and anti-DNAseB), hepatitis B serology and hepatitis C RNA assay, HIV serology and blood cultures if the patient is febrile.

8. If the kidney size is normal and the diagnosis is still uncertain, a renal biopsy is indicated.

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