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: Shivani Chaparala M.B.B.S [2]Ahmed Younes M.B.B.CH [3]

Overview

Early Diagnostic paracentesis (needle drainage of the ascitic fluid performed in < 72hrs) is recommended in all cirrhotic patients with ascites. Paracentesis reveals an ascitic fluid with a total white cell count of up to 500 cells/mcL, a high polymorphonuclear (PMN) cell count (250/mm³ more). Ascitic fluid analysis and culture must be performed before initiating antibiotic therapy by bedside inoculation of ascitIc fluid ≥ 10 mL into blood culture bottles. Ascitic fluid analysis is the gold standard for the confirmation of the diagnosis of spontaneous bacterial peritonitis. 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 are non-specific. 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

Laboratory tests for the diagnosis and differential diagnosis of SBP
Ascitic fluid analysis	Spontaneous Bacterial Peritonitis	Secondary bacterial peritonitis	Hepatic ascites	Cardiac ascites	Nephrogenic ascites	Pancreatic ascites	Tuberculous ascites	Malignant ascites
Gross appearance	cloudy or turbid	turbid or purulent	clear straw or milky	clear to pale yellow	straw colored or chylous	milky or cloudy or turbid	milky or normal	milky or bloody
Leukocyte count and differential (cells/mm3)	≥ 250 PMN	> 1000 WBC predominantly PMN	< 500 WBC ≥ 250 PMN or normal	< 500 WBC < 250 PMN	< 500 WBC < 250 PMN	< 500 WBC ≥ 250 PMN	≥ 250 PMN or normal	≥ 500 WBC
Total protein	≥ 25 g/L	> 25 g/ L	< 25 g/L	≥ 25 g/L	< 25 g/L	≥ 25 g/L	≥ 25 g/L	≥ 25 g/L
Serum-ascites albumin gradient	≥ 1.1 g/dL	≥ 1.1 g/dL	≥ 1.1 g/dL	≥ 1.1 g/dL	< 1.1 g/dL	< 1.1 g/dL	< 1.1 g/dL	< 1.1 g/dL
LDH(lactate dehydrogenase)	↑or normal	> upper limit of normal for serum LDH	↓	↓ or normal		↑or normal	↑or normal	↑
Glucose	↓	< 50 mg/dL	normal	normal		↓	↓	↓
Amylase	-	-	normal	-	-	↑	-	↑or normal
Tumor markers	-	-	↑or normal	normal	-	↑or normal	↑or normal	↑
Confirmatory tests	single organism in culture, total protein < 1 g/dL, glucose > 50 mg/dl, LDH < 225 units/ L.	poly-microbial infection including anaerobes , total protein > 1 g/dL, glucose < 50 mg/dL, LDH ≥ 225 units/ L. Upright abdominal x-ray, water soluble contrast studies of GI tract	ultrasound and/or liver biopsy	chest x-ray and ekg	24-hour urine protein excretion	Abdominal CT scan	mycobacterial growth on culture of laparoscopic biopsy specimen of peritoneum	search for primary tumor
Additional comments	good clinical response to antibiotics.	Consider surgery if perforation of gut is suspected. CEA >5 ng/ml. Alkaline phosphatase > 240 units/ L.				ascitic fluid amylase > 100 units/ L	laparoscopy, peritoneal biopsy, bacteriology, PCR.	cytology
Relative frequency	-	-	81%	3%	Dialysis associated- 1%	1%	2%	10%

Approach to the diagnosis and treatment of spontaneous bacterial peritonitis

Diagnostic Paracentesis ❑ Perform ascitic fluid cell count and differential ❑ Perform ascitic fluid culture (Inoculated at bedside)

PMN ≥ 250cells/mm³

If YES ❑ Presumptive SBP ❑ Begin empiric antibiotic therapy(eg:Cefotaxime 2g IV q8H and ❑ IV Albumin on day 1 & day 3 IF serum creatinine 1mg/dl, BUN > 30mg/dl or total albumin > 4mg/dl

IF NO ❑ Look for the signs/symptoms of Infection

Is Culture Positive ?

Absent Symptoms ❑ Is Culture Positive?

Symptoms Present ❑ Begin Empiric Antibiotic Therapy for SBP

Negative Culture Culture Negative Neutrocytic Ascites ( CNNA ) ❑ morbidity and mortality same as SBP ❑ Treat as SBP ❑ Complete 5 day Antibiotic Course

Confirmed SBP ❑ Narrow the spectrum based on the susceptibility to complete the 5 day course

Culture Negative ❑ No Antibiotics indicated

Culture Positive Monomicrobial nonneutrocytic Bacterascites: ❑ Followup paracentesis recommended when the culture growth is discovered ❑ ~ 60% spontaneous resolution, ❑ ~ 40% turn to SBP. Polymicrobial bacterascites: ❑ Low morbidity ❑ Majority from traumatic tap ❑ Clinical followup +/- antibiotics is recommended

Routine laboratory studies for spontaneous bacterial peritonitis include:

• Complete blood count and differential count 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 and serum bilirubin to assess the liver function.
• Coagulation profile
• Urine analysis and culture to rule out asymptomatic bacteriuria
• Amylase and Lipase levels to rule out pancreatitis as the cause of ascites
• Procalcitonin level (PCT) level was higher in advanced Liver cirrhosis patients with SBP than culture negative nuerocytic ascites (CNNA) which indicated it may represent as a simple biomarker for differentiating SBP from CNNA. PCT may be a prognostic predictor to guide the empirical antimicrobial therapy in order to decrease the in-hospital mortality and the frequency of complications.

Diagnostic paracentesis:

Performed usually within 72 hrs of admission.

Indications for diagnostic paracentesis
All patients with cirrhosis and ascites and with any of the following:
Upon admission to the hospital
With a change in the clinical course including development of fever, abdominal pain, altered mental status, ileus, or septic shock.
Development of laboratory abnormalities such as a leukocytosis, acidosis, or renal failure.
During episodes of gastrointestinal bleeding prior to the administration of antibiotics.
Worsening of liver function and Hepatic encephalopathy.

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.

Ascitic Fluid Analysis

Ascitic fluid analysis is the gold standard and is required for the confirmation of the diagnosis of spontaneous bacterial peritonitis.

Tests	Diagnostic Values
Cell count with differential	Leukocyte count > 500 cells/mm3 Absolute neutrophil count >250 cells/mm3
Bacterial culture	Usually positive for gram-negative bacteria (mainly Escherichia coli and Klebsiella) and gram-positive cocci (usually Streptococcus spp. and enterococci).
Protein concentration	1 g/dL (10 g/L) or less

Ascitic fluid Culture

• Performed before initiating antibiotic therapy by bedside inoculation of ascitIc fluid ≥ 10 mL into blood culture bottles, instead of sending the fluid to the laboratory in a syringe or container, since immediate inoculation improves the yield on bacterial culture from approximately 65% to 90%, when the ascitic fluid cell count is at least 250 cells/mm³.
• Separate and simultaneous blood cultures should also be obtained, as up to 50% of patients with SBP have concomitant bacteremia.
• Neither sensitive/specific
• But is indicated to rule out secondary peritonitis caused by many organisms usually anaerobes and also to guide and narrow down the appropriate antibiotic of choice based on the culture and sensitivity results.

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

1. Gram stain: To identify the number of organisms causing peritonitis, most helpful in the diagnosis of free perforation of the intestine, where many different organisms are found including gram negative bacteria and anaerobes, fungi.
2. Total protein: 20% of ascitic samples in patients with cirrhosis will have a protein concentration greater than 2.5 g/dL
3. Lactate dehydrogenase: In SBP, the ascitic fluid LDH rises because of the release of LDH from neutrophils, and the concentration will be more than serum concentration. In secondary peritonitis, the levels are even more elevated than in SBP.
4. Glucose: Under normal conditions, and in early SBP, the ascitic fluid glucose concentration is similar to that of serum. By contrast, in SBP detected later in its course, and as well as in the setting of intestinal perforation into ascitic fluid, the ascitic fluid concentration drops to 0 mg/dL because of consumption of glucose by increased numbers of neutrophils and bacteria.
5. Amylase: In uncomplicated ascites in the setting of cirrhosis, the ascitic fluid amylase concentration usually one half that of the serum value. In patients with acute pancreatitis or intestinal perforation (with release of luminal amylase into the ascitic fluid), the fluid amylase concentration is elevated markedly, and approximately five-fold greater than simultaneous serum values.
6. Albumin: It is important for the calculation of serum-ascites albumin gradient , and helps us in identifying the portal hypertension and associated prognosis.
7. Serum-ascites albumin gradient (if not calculated before): SAAG > 1.1 g/dL indicates the presence of portal hypertension. Peritoneal carcinomatosis is the most common cause of a low SAAG.
8. Ascitic Fluid smear and culture: Helps in the identification of tuberculous peritonitis which presents similarly to SBP, with fever, abdominal pain and one half of patients have cirrhosis.
9. Bilirubin: AF bilirubin > 6 mg/dL suggests biliary or small intestinal perforation into AF.
10. Triglyceride: A triglyceride level should be measured in opalescent or frankly milky ascitic fluid. Chylous ascites has a triglyceride concentration greater than serum (200 mg/dL).
11. Cytology: Expensive and is only revealing in the setting of peritoneal carcinomatosis, typically in patients with a history of breast, colon, gastric or pancreatic carcinoma.

• Paracentesis reveals an ascitic fluid with, most commonly:
  • Decreased ascitic opsonic activity.
  • Some patients may have an ascitic neutrophil count <250 cells/mm³ with positive cultures. This is known as "bacterascites". These patients should undergo a repeat 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.

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