Spontaneous bacterial peritonitis laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Govindavarjhulla, M.B.B.S. [2] Guillermo Rodriguez Nava, M.D. [3] Shivani Chaparala M.B.B.S [4]

Overview

• Diagnosis requires paracentesis (needle drainage of the ascitic fluid).
• Ascitic fluid culture is negative in up to 60% of patients with clinical manifestations of spontaneous bacterial peritonitis (SBP)
• Therefore, the diagnosis of SBP is based on the neutrophil count, which reaches its highest sensitivity with a cutoff neutrophil count of > 250/mm³.
• Leukocytosis and acidosis may be present, but they are non-specific findings.
• Plain abdominal X-rays may reveal dilated, oedematous intestines, although it is mainly useful to look for pneumoperitoneum (free air in the peritoneal cavity), which may also be visible on chest X-rays.
• If reasonable doubt still persists, an exploratory peritoneal lavage may be performed (e.g. in the case of trauma, in order to look for white blood cells, red blood cells, or bacteria).

Laboratory Findings

Routine laboratory studies for peritonitis include:

• Ascitic fluid analysis is the gold standard and is required for the confirmation of the diagnosis of spontaneous bacterial peritonitis.
• Complete blood count and differential count are tested to confirm infection.
• BUN, S.creatinine to asses the renal function.
• ABG analysis
• S.glucose
• Blood culture may be useful in sepsis
• Serum electrolytes
• Liver Function tests are to be performed for the evaluation of cirrhosis
• Coagulation profile
• Urine analysis and culture to rule out asymptomatic bacteriuria
• Amylase and Lipase levels to rule out pancreatitis as the cause of ascites

SBP

• Early Diagnostic paracentesis (< 72hrs) is recommended to perform in all cirrhotic patients with ascites:
  • At the time of admission and/or
  • In the case of gastrointestinal (GI) bleeding,
  • Shock,
  • Evident signs of inflammation,
  • Hepatic encephalopathy,
  • Worsening of liver function and/or
  • Renal dysfunction
• Paracentesis reveals an ascitic fluid with, most commonly,
  • A total white cell count of up to 500 cells/mcL with a high polymorphonuclear (PMN) cell count (250/mm³ more) and a
  • Protein concentration of 1 g/dL (10 g/L) or less,
  • Corresponding to decreased ascitic opsonic activity.
• Ascitic fluid analysis and culture performed:
  • Before initiating antibiotic therapy by
  • Bedside inoculation of ascitIc fluid ≥ 10 mL into blood culture bottles.
  • 80-90% positive and provides the highest yield.
• Absoulte neutrophil count - a total count of >250 cells/mm³ confirm the diagnosis of spontaneous bacterial peritonitis.
  • When culture is positive, the most common organisms are Gram-negative bacteria (mainly Escherichia coli) and Gram-positive cocci (usually Streptococcus spp. and enterococci).
  • If the diagnosis is doubtful, the serum procalcitonin level has a 95% sensitivity, and 98% specificity with a 0.75 ng/mL cutoff.
  • Some patients may have an ascitic neutrophil count <250 cells/mm³ with positive cultures. This is known as "bacterascites".
  • These patients should undergo a second paracentesis.
  • Patients with signs of Systemic inflammatory response syndrome (SIRS) or in whom the repeat ascitic neutrophil count is >250 cells/mm³ should receive antibiotic therapy,
  • If not, they should be followed up.
  • Albumin concentration - it is important for the calculation of serum-ascites albumin gradient , this helps us in identifying the portal hypertension and prognosis.
  • Protein concentration - low protein concentration is noticed in cases of spontaneous bacterial peritonitis which differentiates it from secondary bacterial peritonitis where it is normal.
• Recently leukocyte esterase calibrated reagent strips (LERS) to assess the PMN cell count (cut-off of > 250 PMN/mcL) are promised to provide good screening results when the strip turns any hue of tan/brown at 3 min. High degree of sensitivity, but the sensitivity is too low for routine use.

Ascitic Fluid Analysis

• A high index of suspicion must exist for ascitic fluid infection in a cirrhotic patient. Given the similarities in presentation between the variants of ascitic fluid infection and the inability to clinically distinguish spontaneous from secondary peritonitis, the diagnosis of SBP should be through abdominal paracentesis as it has been shown to be safe with a low risk for complication, even in patients with marked coagulopathy and thrombocytopenia.

Diagnostic paracentesis

• Performed in all cirrhotics with ascites:

1. upon admission to the hospital
2. who develop any change in clinical status including fever, abdominal pain, mental status changes, ileus, or septic shock
3. who develop laboratory abnormalities such as a leukocytosis, acidosis, or renal failure
4. during episodes of gastrointestinal bleeding prior to the administration of antibiotics

• The following tests are recommended for suspected infection of the ascitic fluid:

1. Cell counts with differential : Absoulte neutrophil count - a total count of >250 cells/mm³ confirm the diagnosis of spontaneous bacterial peritonitis.most sensitive and single best

test in diagnosing ascitic fluid infection [45]. Not all cases in which the PMN count is above this threshold represent infection, and values in this range can be seen with hemorrhage into ascites, peritoneal carcinomatosis, or pancreatic ascites. A useful distinguishing feature is that the PMN is usually not the predominant cell type in these cases

1. Culture (in blood culture bottles)
2. Gram’s stain
3. Total protein
4. Lactate dehydrogenase
5. Glucose
6. Amylase
7. Albumin (if SAAG unknown)
8. Serum-ascites albumin gradient (if not calculated before)

• Given the rapidity (90 s), low cost, and availability ‘dipstick’ testing of ascites allows for more rapid diagnosis and management of SBP.

References

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