Peritonitis laboratory findings

Peritonitis Main Page
Patient Information
Overview
Causes
Classification Spontaneous Bacterial Peritonitis Secondary Peritonitis
Differential Diagnosis

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

Overview

• Diagnosis requires paracentesis (needle drainage of the ascitic fluid). Ascites culture is negative in up to 60% of patients with clinical manifestations of spontaneous bacterial peritonitis (SBP), therefore, the diagnosis is based on the neutrophil count, which reaches its highest sensitivity with a cutoff neutrophil count of > 250/mm³.
• A diagnosis of peritonitis is based primarily on clinical grounds, that is on the clinical manifestations described above; if they support a strong suspicion of peritonitis, no further investigation should delay surgery. Leukocytosis and acidosis may be present, but they are not 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 cause of trauma, in order to look for white blood cells, red blood cells, or bacteria).

Laboratory Findings

Routine laboratory studies for peritonitis include:

Laboratory tests, most importantly ascitic fluid analysis is required for confirmation of 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 case of gastrointestinal (GI) bleeding, shock, signs of inflammation, hepatic encephalopathy, worsening of liver or renal function. 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/mcL or 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 ascites ≥ 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". This 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.
• Secondary bacterial peritonitis should be suspected if the ascites PMN count is 250 cells/mm3 and:

'two' of the following 'three' ascitic fluid values are met: 

(1) glucose !50 mg/dl (2) total protein 11 g/dl and (3) lactate dehydrogenase greater than the upper limit of normal for serum. Gut perforation can be predicted with 100% sensitivity (but only 45% specificity) using these criteria. Nonetheless, patients who fulfill two of these criteria must undergo immediate flat and upright abdominal X- rays, and if negative, water-soluble contrast studies of the gastrointestinal tract or abdominal computed tomography. The finding of more than one organism on Gram’s stain or culture of ascitic fluid should prompt a similar urgent evaluation for perforation.