Spontaneous bacterial peritonitis differential diagnosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Shivani Chaparala M.B.B.S [2];Ahmed Younes M.B.B.CH [3]


SBP must be differentiated from other abdominal conditions presenting with fever and abdominal pain. It also has to be differentiated from secondary peritonitis, chemical peritonitis, peritoneal dialysis peritonitis, chronic tuberculous peritonitis.

Differentiating Spontaneous bacterial peritonitis from other Diseases

Spontaneous bacterial peritonitis presents with fever and abdominal pain. Diseases presenting with similar features include:

Differentiating secondary peritonitis from spontaneous bacterial peritonitis
Characteristic Spontaneous bacterial peritonitis Secondary peritonitis
  • Similar presentation but insidious onset unlike rapid onset in SBP
  • Polymicrobial involvement is common
  • Identifiable source of intra-abdominal infection, with or without perforation (surgically treatable source)[1]
Diagnostic criteria SBP is diagnosed in the presence of:[2] Diagnosed in the presence of
Follow-up paracentesis
Differentiating SBP from other causes of peritonitis
Disease Prominent clinical findings Lab tests Tratment
Primary peritonitis Spontaneous bacterial peritonitis
Tuberculous peritonitis
Continuous Ambulatory Peritoneal Dialysis (CAPD peritonitis)
Secondary peritonitis Acute bacterial secondary peritonitis
Biliary peritonitis
Tertiary peritonitis
Familial Mediterranean fever (periodic peritonitis, familial paroxysmal polyserositis)
  • Colchicine prevents but does not treat acute attacks.
Granulomatous peritonitis
  • Diagnosed by the demonstration of diagnostic Maltese cross pattern of starch particles.
Sclerosing encapsulating peritonitis
Intraperitoneal abscesses
  • Diagnosed best by CT scan of the abdomen.
  • Treatment consists of prompt and complete CT or US guided drainage of the abscess, control of the primary cause, and adjunctive use of effective antibiotics. Open drainage is reserved for abscesses for which percutaneous drainage is inappropriate or unsuccessful.
Peritoneal mesothelioma
peritoneal carcinomatosis

Differentiating spontaneous bacterial peritonitis from other diseases that may cause abdominal pain

Classification of acute abdomen based on etiology Presentation Symptoms Signs Diagnosis Comments
Fever Abdominal Pain Jaundice Guarding Rebound Tenderness Bowel sounds Lab Findings Imaging
Common causes of Peritonitis Primary Peritonitis Spontaneous bacterial peritonitis + Diffuse - - - Hypoactive
  • Ascitic fluid PMN>250 cells/mm³
  • Culture: Positive for single organism
Ultrasound for evaluation of liver cirrhosis -
Secondary Peritonitis Perforated gastric and duodenal ulcer + Diffuse - + + N
    • Glucose < 50mg/dl
    • Total protein > 1g/dl
Air under diaphragm in upright CXR Upper GI endoscopy for diagnosis
Acute cholangitis + RUQ + - - N Abnormal LFT Ultrasound shows biliary dilatation Biliary drainage (ERCP) + IV antibiotics
Acute cholecystitis + RUQ + - - Hypoactive Ultrasound shows gallstone and evidence of inflammation Murphy’s sign
Acute pancreatitis + Epigastric +/- - - N Increased amylase / lipase Ultrasound shows evidence of inflammation Pain radiation to back
Acute appendicitis + RLQ - + + Hypoactive Leukocytosis Ultrasound shows evidence of inflammation Nausea & vomiting, decreased appetite
Acute diverticulitis + LLQ +/- + - Hypoactive Leukocytosis CT scan and ultrasound shows evidence of inflammation
Acute salpingitis + LLQ/ RLQ - +/- +/- N Leukocytosis Pelvic ultrasound Vaginal discharge
Hollow Viscous Obstruction Small intestine obstruction - Diffuse - + +/- Hyperactive then absent Leukocytosis Abdominal X ray Nausea & vomiting associated with constipation, abdominal distention
Volvulus - Diffuse - + - Hypoactive Leukocytosis CT scan and abdominal X ray Nausea & vomiting associated with constipation, abdominal distention
Biliary colic - RUQ + - - N Increased bilirubin and alkaline phosphatase Ultrasound Nausea & vomiting
Renal colic - Flank pain - - - N Hematuria CT scan and ultrasound Colicky abdominal pain associated with nausea & vomiting
Vascular Disorders Ischemic causes Mesenteric ischemia +/- Periumbilical - - - Hyperactive Leukocytosis and lactic acidosis CT scan Nausea & vomiting, normal physical examination
Acute ischemic colitis +/- Diffuse - + + Hyperactive then absent Leukocytosis CT scan Nausea & vomiting
Hemorrhagic causes Ruptured abdominal aortic aneurysm - Diffuse - - - N Normal CT scan Unstable hemodynamics
Intra-abdominal or retroperitoneal hemorrhage - Diffuse - - - N Anemia CT scan History of trauma
Gynaecological Causes Ovarian Cyst Complications Torsion of the cyst - RLQ / LLQ - +/- +/- N Increased ESR and CRP Ultrasound Sudden onset sever pain with nausea and vomiting
Cyst rupture - RLQ / LLQ - +/- +/- N Increased ESR and CRP Ultrasound Sudden onset sever pain with nausea and vomiting
Pregnancy Ruptured ectopic pregnancy - RLQ / LLQ - - - N Positive pregnancy test Ultrasound History of missed period and vaginal bleeding


  1. Runyon BA, Hoefs JC (1984). "Ascitic fluid analysis in the differentiation of spontaneous bacterial peritonitis from gastrointestinal tract perforation into ascitic fluid". Hepatology. 4 (3): 447–50. PMID 6724512.
  2. Runyon BA, Hoefs JC (1986). "Spontaneous vs secondary bacterial peritonitis. Differentiation by response of ascitic fluid neutrophil count to antimicrobial therapy". Arch Intern Med. 146 (8): 1563–5. PMID 3729637.
  3. Runyon BA (1986). "Bacterial peritonitis secondary to a perinephric abscess. Case report and differentiation from spontaneous bacterial peritonitis". Am J Med. 80 (5): 997–8. PMID 3518442.
  4. Akriviadis EA, Runyon BA (1990). "Utility of an algorithm in differentiating spontaneous from secondary bacterial peritonitis". Gastroenterology. 98 (1): 127–33. PMID 2293571.