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


  • 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

Peritoneal Fluid Analysis - Gross appearance
Peritoneal Fluid Analysis – Gross appearance

Paracentesis biochemistry

Paracentesis biochemistry
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
The Serum-Ascites Albumin Gradient (SAAG)

Microscopy and analysis

paracentesis Microscopy and analysis

References and Links

CCC 700 6

Critical Care


BA MA (Oxon) MBChB (Edin) FACEM FFSEM. Emergency physician, Sir Charles Gairdner Hospital.  Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |

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