1. PERITONEAL FLUID
    The common indications for paracentesis are ascites of unknown origin, suspected intestinal perforation, haemorrhage or infarct, infections like tuberculosis, complications of cirrhosis (spontaneous bacterial peritonitis) and suspected intra-abdominal malignant disorders. To distinguish between ascites caused by liver disease and malignancy, the serum-ascites albumin concentration gradient is more reliable than the ascitic fluid-to-serum ratio for either total protein or LD. The serum-ascites albumin gradient is greater in transudate (1.6±0.5 g/dl) than exudates (0.6±0.4 g/dl). Peritoneal lavage is useful in evaluating the conditions of patients with blunt trauma. Peritoneal lavage consists of inserting a peritoneal dialysis catheter into the abdominal cavity through a small midline infra-umbilical incision. The catheter is aspirated and, if blood is not grossly observed, 1 litre of Ringer’s lactate solution is introduced and immediately retrieved by gravity and interpreted as described in Table . Table depicts various appearances of peritoneal fluid and the associated diseases.
    Criteria for diagnosing blunt and penetrating trauma by peritoneal lavage fluid analysis
    Diagnosis
    Gross findings
    Laboratory findings

Penetrating trauma
Blood in lavage
Blood in drain fluid from Foley’s catheter or chest tube
Evidence of food/foreign particle/bile
RBC count >0.1 million/µl
WBCs count >500/µl
α-Amylase level >twice that of serum

Blunt injury
None of the above gross findings
RBC count <0.025 million/µl WBC count <100/µl α-Amylase level

Appearance of peritoneal fluid and associated diseases
Appearance
Disease

Clear, pale-yellow
Cirrhosis

Cloudy, turbid
Bacterial peritonitis, pancreatitis, malignancy

Green
Biliary tract disease, ruptured viscera

Bloody
Trauma, malignancy, pancreatitis, intestinal infarction

Milky
Chylous ascites, trauma, malignancy

MICROSCOPY
Smears are made and stained as usual. A differential cell count with more than 25% neutrophils is considered abnormal. A predominance of neutrophils is suggestive of bacterial infection and an absolute neutrophil count of more than 250/µl is indicative of spontaneous or secondary bacterial peritonitis. A predominance of lymphocytes is seen in congestive cardiac failure, cirrhosis, nephrotic syndrome, chylous effusions, tuberculosis peritonitis and malignant disorders. The fluid is also examined for malignant cells.
CHEMICAL ANALYSIS
Protein
Total protein estimation has little value in differentiating between transudates and exudates. A serum-ascites albumin ratio gives a better discrimination.

Glucose
A simultaneous plasma-fluid glucose ratio of 1.0 or more is suggestive of tuberculosis and abdominal carcinomatosis, a ratio of less than 1.0 is seen in cases of cirrhosis or congestive heart failure.
Enzymes
α-Amylase in the peritoneal fluid is increased in acute or traumatic pancreatitis or pancreatic pseudocysts, However, lipase determination is more reliable in the diagnosis of pancreatitis. A higher level of alkaline phosphatase in the fluid than in the blood is seen in patients with bowel strangulation, intestinal perforation or traumatic haemoperitoneum. A lactate dehydrogenase ratio of more than 0.6 of ascitic fluid and blood is suggestive of an abdominal malignancy.
Tumour Markers
Carcino-embryonic antigen (CEA) suggests malignancy as a cause of peritoneal fluid accumulation.

Approach for tumour marker interpretation
T200=Panleukocyte antigen, EMA=Epithelial Membrane Antigen, TdT=Terminal deoxynucleotidyl Transferase, CALLA=Common Acute Lymphoblastic Leukaemia Antigen, CEA=Carcinoembryonic Antigen, GFAP=Glial Fibrillary Acidic Protein

MICROBIOLOGIC EXAMINATION
A culture of peritoneal fluid is often required to identify the microorganisms of tuberculosis peritonitis and spontaneous bacterial peritonitis. This should include aerobic, anaerobic cultures and for organisms requiring CO2, like Streptococcus pneumoniae. Bacterial antigens can be detected by agglutination or counter-immunoelectrophoresis.

Findings

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