Peritoneal fluid analysis is a diagnostic laboratory procedure used to assess the fluid found in the peritoneal cavity—the space between the layers of the peritoneum, which lines the abdominal wall and covers abdominal organs. Normally, this space contains only a small amount of fluid for lubrication. However, in pathological conditions such as ascites, peritonitis, malignancy, or liver disease, the volume and composition of peritoneal fluid can change significantly.

 

🧪 Peritoneal Fluid Analysis: A Diagnostic Overview

🩸 Introduction

Analyzing this fluid can provide critical information regarding the cause of fluid accumulation, presence of infection, inflammation, or cancer.

🩼 Indications for Peritoneal Fluid Analysis

Peritoneal fluid analysis is recommended when patients present with:

• Unexplained abdominal distension or pain

• Suspected spontaneous bacterial peritonitis (SBP)

• Suspected malignancy with ascites

• Chronic liver disease with complications

• Abdominal trauma

• Suspected tuberculous peritonitis

💉 Sample Collection: Paracentesis Procedure

Peritoneal fluid is obtained via paracentesis, a minimally invasive procedure where a needle is inserted into the abdominal cavity under sterile conditions.

🔹 Technique:

• Performed under ultrasound guidance if needed.

• Patient is in supine or semi-reclining position.

• Site commonly used: 2 cm below the umbilicus or in the left lower quadrant.

• Approximately 20–50 mL of fluid is collected in sterile containers.

🔸 Safety Notes:

• Avoid in patients with coagulopathy or bowel obstruction unless necessary.

• Monitor for complications such as perforation, bleeding, or infection.

🔬 Macroscopic Examination

The gross appearance of peritoneal fluid provides immediate clues:

Appearance	Possible Indication
Clear, straw-colored	Transudate (e.g., cirrhosis)
Cloudy or turbid	Infection (bacterial peritonitis)
Milky or chylous	Lymphatic obstruction, malignancy
Bloody	Trauma, malignancy, hemorrhagic ascites
Greenish	Bowel perforation, bile leakage

🧫 Biochemical Analysis

🔹 1. Serum-Ascites Albumin Gradient (SAAG)

• SAAG = Serum Albumin – Ascitic Fluid Albumin

• ≥1.1 g/dL: Suggests portal hypertension (e.g., cirrhosis, heart failure)

• <1.1 g/dL: Indicates non-portal causes (e.g., malignancy, infection)

🔹 2. Total Protein

• <2.5 g/dL: Transudative fluid (cirrhosis, nephrotic syndrome)

• >2.5 g/dL: Exudative fluid (infections, malignancy, pancreatitis)

🔹 3. Lactate Dehydrogenase (LDH)

• Elevated in infection, malignancy, tuberculosis

• Compared to serum LDH to classify fluid as exudative or transudative

🔹 4. Glucose

• Low glucose (<50 mg/dL) seen in SBP, tuberculosis, malignancy

🔹 5. Amylase

• Elevated in pancreatic ascites or bowel perforation

🔍 Microscopic and Cytological Examination

🔹 Cell Count and Differential

• Neutrophils >250 cells/mm³: Diagnostic for spontaneous bacterial peritonitis (SBP)

• Lymphocyte predominance: Suggests tuberculous or carcinomatous peritonitis

• RBC count elevated in trauma or malignancy

🔹 Gram Stain and Culture

• Gram stain may reveal bacteria in SBP or secondary peritonitis

• Cultures are vital for detecting specific pathogens:

  • Aerobic and anaerobic cultures

  • Use bedside inoculation into blood culture bottles for higher yield

🔹 Acid-Fast Bacilli (AFB) Stain and Culture

• For suspected tuberculous peritonitis

• AFB culture is slow but specific; PCR may aid early diagnosis

🔹 Cytology

• Detects malignant cells in peritoneal fluid

• Useful in diagnosing peritoneal carcinomatosis from ovarian, gastric, pancreatic, or colon cancer

🧪 Special Tests

• Triglyceride levels (>110 mg/dL): Suggest chylous ascites

• Bilirubin levels in fluid > serum bilirubin: May indicate bile leak

• ADA (Adenosine Deaminase): Elevated in tuberculosis

📊 Interpreting Results: Common Conditions

Condition	SAAG	Protein	WBC Count	Glucose	LDH	Cytology
Cirrhosis	>1.1	Low	Low	Normal	Low	Negative
Malignancy	<1.1 or >1.1	High	Moderate	Low	High	Positive
SBP	>1.1	Low	>250 (neutrophils)	Low	High	Negative
Tuberculosis	<1.1	High	Lymphocyte predominant	Low	High	Negative
Pancreatic Ascites	<1.1	High	High	Low	High	Negative

🧠 Clinical Importance

Peritoneal fluid analysis plays a crucial role in:

• Distinguishing between transudative and exudative ascites

• Early diagnosis and treatment of peritonitis

• Identifying malignancy and tuberculosis

• Monitoring patients with chronic liver disease or renal failure

✅ Conclusion

Peritoneal fluid analysis is an essential diagnostic tool that provides detailed insight into intra-abdominal pathologies. By integrating clinical presentation with fluid analysis results—including gross appearance, biochemistry, cytology, and microbiology—clinicians can make timely and accurate diagnoses, leading to better patient outcomes. Regular use in hospital and critical care settings has made it an indispensable procedure in internal medicine and gastroenterology.

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