What to send for analysis from ascites (accumulation of fluid in the peritoneal cavity)?

From the Guidelines

For ascites fluid analysis, send the following samples: cell count and differential, albumin, total protein, and Gram stain and culture, as these tests are essential to determine the cause of ascites, detect infection, and guide treatment 1. When analyzing ascites fluid, it is crucial to prioritize tests that help identify the underlying cause of ascites and detect potential infections, such as spontaneous bacterial peritonitis (SBP).

• Cell count and differential: to identify the presence of neutrophils, which can indicate SBP
• Albumin: to calculate the serum-ascites albumin gradient (SAAG), which helps differentiate between portal hypertension-related and non-portal hypertension-related causes of ascites
• Total protein: to assess the risk of SBP, as patients with low protein concentration (<15 g/L) are at increased risk
• Gram stain and culture: to detect bacterial infection and guide antibiotic therapy Additionally, consider sending:
• Cytology (if malignancy is suspected)
• Amylase (if pancreatic ascites is suspected)
• Triglycerides (if chylous ascites is suspected) These tests should be performed on at least 50 mL of ascitic fluid collected in sterile containers, and samples should be sent immediately to the laboratory for processing 1. The most recent guidelines emphasize the importance of ascitic fluid culture to help guide antibiotic therapy, and patients with culture-negative neutrocytic ascites should be treated similarly to those with culture-positive SBP, as both groups have significant morbidity and mortality 1.

From the Research

Ascites Analysis

To determine the cause of ascites, the following should be sent for analysis:

• Cell count and albumin in the ascitic fluid, along with simultaneous determination of serum albumin to determine the serum: ascites albumin gradient 2
• Total protein concentration, cell count and differential 3
• Optional analysis includes:
  • Cholesterol
  • Fluid culture
  • Cytology
  • Tumor markers
  • Lactate dehydrogenase
  • Adenosine deaminase (ADA)
  • Triglyceride
  • Amylase
  • Glucose
  • Brain natriuretic peptide (BNP) 3
• Ascitic fluid cultures to rule out spontaneous bacterial peritonitis 4, 5
• Ascitic amylase and mycobacterial cultures/PCR when there is strong suspicion for tuberculosis and pancreatitis, respectively 4
• Ascitic cytology when cancer is suspected 4

Diagnostic Approach

The diagnostic approach to ascites involves:

• Abdominal ultrasonography 4
• Diagnostic paracentesis 4, 5
• Examination of ascitic fluid to rule out spontaneous bacterial peritonitis 5
• Determination of the serum-ascites albumin gradient to assess the cause of ascites 2, 6