From the Guidelines
Analyzing ascitic fluid obtained from paracentesis involves several key tests to diagnose conditions like spontaneous bacterial peritonitis, malignancy, or portal hypertension, with the most recent and highest quality study 1 guiding the approach. To analyze the fluid, first, collect it in appropriate containers: sterile tubes for culture, EDTA tubes for cell count, and plain tubes for biochemical analysis. Begin with a visual inspection noting color, clarity, and viscosity. Cloudy fluid suggests infection while bloody fluid may indicate trauma or malignancy. Perform cell counts including white blood cell count with differential (>250 neutrophils/mm³ suggests infection) and red blood cell count. Measure protein, albumin, and calculate the serum-ascites albumin gradient (SAAG); a SAAG ≥1.1 g/dL indicates portal hypertension while <1.1 g/dL suggests other causes like malignancy or tuberculosis. Culture the fluid for bacteria using blood culture bottles at the bedside for better yield. Additional tests include glucose (decreased in infection), lactate dehydrogenase (elevated in infection or malignancy), amylase (elevated in pancreatic ascites), and cytology for malignant cells. For suspected tuberculosis, request adenosine deaminase and acid-fast bacilli testing. These comprehensive tests help determine the underlying cause of ascites and guide appropriate treatment, prioritizing morbidity, mortality, and quality of life as outcomes, as emphasized in the management of patients with decompensated cirrhosis 1.
Some key points to consider:
- A diagnostic paracentesis should be performed in all patients with new onset grade 2 or 3 ascites, or in those hospitalized for worsening of ascites or any complication of cirrhosis 1.
- Neutrophil count and culture of ascitic fluid should be performed to exclude bacterial peritonitis, with a neutrophil count above 250 cells/µl indicating spontaneous bacterial peritonitis (SBP) 1.
- Ascitic total protein concentration should be performed to identify patients at higher risk of developing SBP 1.
- The SAAG should be calculated when the cause of ascites is not immediately evident, and/or when conditions other than cirrhosis are suspected 1.
- Cytology should be performed to differentiate malignancy-related from non-malignant ascites 1.
By following these guidelines and prioritizing the most recent and highest quality evidence 1, healthcare providers can ensure that patients with ascites receive timely and effective diagnosis and treatment, ultimately improving morbidity, mortality, and quality of life outcomes.
From the Research
Analyzing Ascitic Fluid
To analyze ascitic fluid obtained from paracentesis, several factors should be considered:
- The gross appearance of the ascitic fluid, including its color and clarity, can provide useful information, but its diagnostic accuracy is limited 2, 3
- Laboratory analysis, including cell count and culture results, is essential for diagnosing spontaneous bacterial peritonitis (SBP) and other conditions 2, 4
- The serum ascites albumin gradient (SAAG) score can aid in determining portal hypertension as an underlying cause of ascites, but it may not always be accurate 5
Diagnostic Tests
The following diagnostic tests can be used to analyze ascitic fluid:
- Cell count, including absolute neutrophil count, to diagnose SBP 2, 4
- Culture results to identify the infecting organism 2, 4
- Gram's stain, although its sensitivity is low and it is rarely helpful in the evaluation of the ascites patient 6
- SAAG score to determine portal hypertension 5
Interpretation of Results
When interpreting the results of ascitic fluid analysis, consider the following:
- A high index of suspicion for SBP should exist in patients with cirrhosis and ascites, and diagnostic abdominal paracentesis should be performed in all patients admitted to the hospital, during times of worsening clinical appearance, or when gastrointestinal bleeding occurs 4
- Empirical therapy is recommended after paracentesis if suspicion for infection exists, and cefotaxime is the best-studied antibiotic for this purpose 4
- The results of the ascitic fluid analysis should be considered in conjunction with the patient's clinical presentation and medical history to make an accurate diagnosis and develop an effective treatment plan 2, 4