Investigations for Suspected Sepsis with Acute Kidney Injury
For patients with suspected sepsis and acute kidney injury (AKI), a comprehensive diagnostic workup should include blood tests, urinalysis, cultures, imaging, and biomarkers to determine etiology, severity, and guide management.
Initial Laboratory Investigations
Blood Tests
- Complete blood count with differential (leukocytosis with left shift suggests infection) 1
- Serum creatinine and blood urea nitrogen (BUN) to stage AKI severity using KDIGO criteria 2
- Serum electrolytes (sodium, potassium, bicarbonate) - monitor at least every 48 hours 1
- Liver function tests (bilirubin, transaminases, alkaline phosphatase)
- Coagulation profile (PT, INR, aPTT) to assess for coagulopathy 1
- Arterial blood gas analysis to evaluate acid-base status 1
- Lactate levels (marker of tissue hypoperfusion in sepsis) 1
- Blood glucose monitoring every 1-2 hours until stable 1
Cultures and Infection Workup
- Blood cultures (at least two sets from different sites) before antibiotic administration 1
- Urine culture 1
- Cultures from suspected sources of infection (respiratory, wound, etc.) 1
- Procalcitonin (may help differentiate sepsis from non-infectious causes) 2
Urinalysis and Kidney-Specific Tests
- Urinalysis with microscopy (for casts, cells, proteinuria, hematuria) 1
- Urine sodium and fractional excretion of sodium (FENa) to differentiate prerenal from intrinsic causes 1
- Urine osmolality 2
- Protein-to-creatinine ratio or albumin-to-creatinine ratio 1
- Consider novel biomarkers when available:
Imaging Studies
- Renal ultrasound (first-line imaging for all AKI cases) to assess:
- Chest X-ray to evaluate for pneumonia or pulmonary edema 1
- Consider CT scan without contrast if ultrasound is inconclusive 1, 2
Specialized Investigations for Cirrhotic Patients
- Diagnostic paracentesis (mandatory in cirrhotic patients with ascites and AKI) to rule out spontaneous bacterial peritonitis 1
- Ascitic fluid cell count, culture, and albumin level 1
- If pleural effusion is present, diagnostic thoracentesis 1
- Urinary NGAL (can help distinguish acute tubular necrosis from hepatorenal syndrome) 2
Cardiac Assessment
- ECG to assess for cardiac involvement
- Consider echocardiography to evaluate cardiac function and volume status in hemodynamically unstable patients 2
Monitoring Parameters
- Vital signs with early warning scores (e.g., NEWS2) 1
- Fluid balance (intake and output) and daily weight 1
- Urine output (hourly in critically ill patients) 2
- Hemodynamic parameters in unstable patients 1
Timing Considerations
- Initial investigations should be performed immediately upon presentation
- Serum creatinine and electrolytes should be monitored at least every 48 hours or more frequently in critically ill patients 1
- Cultures should be obtained before antibiotic administration to maximize yield 1
Pitfalls and Caveats
- Point-of-care glucose testing using capillary blood may be inaccurate in critically ill patients; arterial blood is preferred if an arterial line is available 1
- FENa may be unreliable in patients who have recently received diuretics 1
- Contrast agents should be avoided for imaging when possible to prevent contrast-induced nephrotoxicity 1
- Biomarkers should be interpreted within specific clinical contexts and not in isolation 2
- Delay in obtaining cultures before antibiotic administration increases mortality by approximately 10% for every hour in septic shock 1
By systematically applying these investigations, clinicians can rapidly identify the cause of AKI in sepsis, determine appropriate interventions, and monitor response to therapy, ultimately improving patient outcomes.