What initial investigations are recommended for a patient suspected of having peritonitis?

Initial investigations recommended for a patient suspected of having peritonitis include:

• Perform a thorough clinical assessment to identify the source of infection and signs of systemic involvement, as per sepsis guidelines.
• Take microbiological and blood samples before starting antimicrobial treatment, including blood cultures, full blood count, C-reactive protein (CRP), urea and electrolytes, creatinine, liver function tests, clotting screen, and blood gas analysis including lactate and glucose measurement.
• Consider urine analysis and chest X-ray to identify possible sources of infection.
• If no likely source of infection is identified after clinical examination and initial tests, consider imaging of the abdomen and pelvis, typically with contrast-enhanced CT scan, to confirm diagnosis, assess severity, and plan therapy.
• Involve surgical or interventional radiology teams early if surgical or radiological intervention is likely to be needed.

These investigations help confirm the diagnosis of peritonitis, identify the underlying cause, and guide urgent management decisions.

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