Peritoneal Fluid Analysis

Peritoneal fluid (ascitic fluid) analysis

The peritoneum is a tough semi-permeable membrane lining abdominal and visceral cavities. it encloses, supports and lubricates organs within the cavity. Paracentesis is effectively the analysis of ‘Ascites’ – the abnormal accumulation of fluid within the abdomen.

• The peritoneum is important in osmoregulation
  • Passive diffusion of water and solute (up to a certain size)
  • Maintains osmotic and chemical equilibrium with blood and lymph
• Ascites develops either from:
  • Increased  accumulation
    • Increased capillary permeability
    • Increased venous pressure
    • Decreased protein (oncotic pressure)
  • Decreased clearance
    • Increased lymphatic obstruction

Cause

• Transudate (<30g/L protein) (Systemic disease)
  • Liver (Cirrhosis)
  • Cardiac e.g. RHF, CCF, SBE right heart valve disease and constrictive Pericarditis
  • Renal failure
  • Hypoalbuminaemia (nephrosis)
• Exudate (>30g/L protein) (Local disease)
  • Malignancy
  • Venous obstruction e.g. Budd-Chiari, Schistosomiasis
  • Pancreatitis
  • Lymphatic obstruction
  • Infection (especially TB)

Analysate interpretation

Gross appearance

Paracentesis biochemistry

Exudate Serum:Ascites Ratios

• Evidence for these ascites:serum ratios is controversial
  • Ascitic fluid protein/Serum Protein >0.5
  • Ascitic Fluid LDH/Serum LDH >0.6
  • Ascitic Fluid LDH >400
• Presence of any 2 of these three findings is usually associated with TB, Malignancy or Pancreatitis
• Absence of all three usually indicates hepatic cause

The Serum-Ascites Albumin Gradient (SAAG)

• The SAAG has become more favored in helping to characterize ascites fluid
• The concept surrounds oncotic-hydrostatic balance
• Simple calculation:
  • Serum albumin – Ascites albumin= SAAG

Microscopy and analysis

References and Links

• CCC – Ascitic fluid