Microbiology:
Cell count and culture: Plain or heparin tubes or sterile yellow containers
Biochemistry:
Heparin tube preferred. Depending on the sample quality and test required, fluid from yellow container can be used.
Fluoride tube for glucose.
For SAAG (see below), a blood sample (heparin preferred) for plasma albumin must be collected within the same day, preferably within 2 hours.
Ascitic fluid pH testing requires collection into capped, bubble-free blood-gas syringe (as with pleural fluid pH).
Paracentesis is performed to establish the cause of ascites, diagnose bacterial peritonitis or for therapeutic purposes. The most common cause for ascites is cirrhosis (80%); other causes include malignancy, cardiac failure or pancreatic ascites.
Cell count: PMN > 250 x 106/L strongly suggests spontaneous bacterial peritonitis (SBP).
Ascitic fluid total protein <10 g/L though not diagnostic, confers increased risk for SBP.
Ascitic fluid pH is typically decreased in SBP (pH<7.35 or blood-ascitic fluid pH gradient >or= 0.1). It can also be decreased in malignant ascites, pancreatic ascites and TB peritonitis. Ascitic fluid pH may assist SBP diagnosis only if there is significant rise in PMN count.
SAAG = serum albumin - ascitic fluid albumin
SAAG replaces the transudate/exudate concept which does not work well for ascitic fluid. It reflects oncotic-hydrostatic balance and is a marker of portal hypertension.
Traditionally literature described SAAG >or= 11g/L is associated with portal hypertension
and SAAG < 11g/L associated with non- portal hypertension related conditions
However, provisional findings from our in house evaluation (using Roche Modular albumin assay) suggest that using cut point of 15g/L instead of 11g/L may improve sensitivity to detect non-portal hypertension related conditions without significantly losing specificity.
Cirrhosis
Alcoholic hepatitis
Massive liver metastasis
Fatty liver of pregnancy
Fulminant hepatic failure
Mixed ascites (e.g. cirrhosis with peritoneal TB)
Portal vein thrombosis / Budd-Chiari syndrome
Peritoneal caricinomatosis
Tuberculosis peritonitis
Pancreatic ascites
Biliary ascites
Bowel obstruction or infarction
| Test | Utility |
|---|---|
| LD (lactate dehydrogenase) | Increased in malignancy-associated ascites |
| Amylase | Increased in pancreatic ascites e.g. acute pancreatitis, but can also be raised in small bowel perforation/ischaemia |
| ADA (adenosine deaminase) | Elevated ADA (>39 U/L) seen in TB peritonitis |
| Glucose | Reduced in TB peritonitis (ratio to blood glucose <0.7). Also reduced in peritoneal carcinomatosis and SBP. |
| Creatinine | Increased above plasma level in urinary leakage into peritoneal cavity |
| Triglyceride | Usually 2-8x above plasma level in chylous ascites |
| Bilirubin | Increased in biliary leakage into peritoneal cavity |
| CEA | Not sensitive for diagnosis; may be used in gastric cancer prognosis |
1. Tarn AC, Lapworth R. Biochemical analysis of ascitic (peritoneal) fluid: what should we measure? Ann Clin Biochem. Sep 2010;47(Pt 5):397-407.
2. Sleisenger MH, Feldman M, Friedman LS, Brandt LJ. Sleisenger and Fordtran's gastrointestinal and liver disease : pathophysiology, diagnosis, management. 9th ed. Philadelphia , PA: Saunders/Elsevier; 2010.
3. Runyon BA. Management of adult patients with ascites due to cirrhosis: an update. Hepatology. Jun 2009;49(6):2087-2107.
4. Wong CL, Holroyd-Leduc J, Thorpe KE, Straus SE. Does this patient have bacterial peritonitis or portal hypertension? How do I perform a paracentesis and analyze the results? JAMA. 2008;299:1166-1178