What are the steps to clinically diagnose peritonitis?

From the Guidelines

The clinical diagnosis of peritonitis should begin with a thorough history and physical examination, including routine laboratory studies, to identify patients with suspected intra-abdominal infection, as recommended by the Surgical Infection Society and the Infectious Diseases Society of America 1. The diagnosis of peritonitis involves a systematic approach, starting with a thorough history and physical examination to identify cardinal signs such as diffuse abdominal pain, abdominal tenderness with guarding, rebound tenderness, and rigidity.

Key Diagnostic Steps

• Specific physical exam maneuvers are essential, such as testing for peritoneal signs through percussion tenderness and assessing for involuntary guarding.
• Laboratory tests should include a complete blood count to check for leukocytosis, C-reactive protein, and procalcitonin levels.
• Diagnostic paracentesis is crucial when ascites is present, with fluid analysis for cell count, protein, glucose, lactate dehydrogenase, Gram stain, and culture.
• Imaging studies, such as abdominal X-rays and ultrasound, can detect fluid collections and free air in perforated viscus cases.
• CT scanning with contrast is the most sensitive imaging modality, identifying inflammation, abscesses, and determining the underlying cause, and is the imaging modality of choice in adult patients not undergoing immediate laparotomy 1. In cases of diagnostic uncertainty, diagnostic laparoscopy may be necessary for direct visualization of the peritoneal cavity.

Importance of Prompt Diagnosis

The diagnosis should be made promptly as peritonitis can rapidly progress to sepsis, with treatment including broad-spectrum antibiotics and surgical intervention when indicated. According to the guidelines, routine history, physical examination, and laboratory studies will identify most patients with suspected intra-abdominal infection for whom further evaluation and management is warranted 1. Further diagnostic imaging is unnecessary in patients with obvious signs of diffuse peritonitis and in whom immediate surgical intervention is to be performed 1.

From the Research

Clinical Diagnosis of Peritonitis

To clinically diagnose peritonitis, the following steps can be taken:

• Physical examination to identify symptoms and signs of peritoneal irritation 2
• Laboratory tests, including:
  • Polymorphonuclear leukocyte (PMN) count in peritoneal fluid, which is the mainstay for diagnosis 3
  • Automated cell count in peritoneal fluid for early screening 3
  • Manual cell count in peritoneal fluid 3
  • Peritoneal fluid culture and bacterial DNA testing in peritoneal fluid 3
• Radiographic tests, although their utility and limitations should be considered 2
• Serum procalcitonin testing as an initial step in the diagnostic algorithm 3

Diagnostic Criteria

The diagnostic criteria for peritonitis in certain patient populations, such as those undergoing continuous ambulatory peritoneal dialysis (CAPD), include:

• Symptoms and signs of peritoneal irritation
• A cloudy effluent with white blood cell (WBC) count greater than 100/microliters
• A positive culture 4
• A peritoneal fluid WBC count cutoff of 230/μL, which provides a good balance between sensitivity and specificity 5

Special Considerations

In patients with advanced liver disease and ascites, spontaneous bacterial peritonitis (SBP) should be suspected, and diagnostic paracentesis and ascitic fluid analysis should be performed promptly 6

• The treatment of SBP typically involves the use of non-nephrotoxic broad-spectrum antibiotics, such as cefotaxime, and may include antibiotic prophylaxis with norfloxacin to prevent recurrence 6