Ascitic Fluid Analysis : How to come to diagnosis?

We have already discussed about the practical essentials about Ascitic Paracentesis including absolute contraindications, site of needle entry and appropriate volume replacement. Laboratory analysis of ascitic fluid may provide answers to important clinical questions, as its composition varies depending on the underlying cause.

Gross	Special test	WBC (/mm³) – most useful	PMN (/mm³)	SAAG (g/dl)	Other testing	Provisional Diagnosis	Further tests
Transparent or Crystal or Cloudy yellow (Neutrophils lead to shimmering effect when sample is glass tube is shaked back and forth in front of light)	PMN > 5000/ cu.mm is quite cloudy.PMN > 50,000/ cu.mm is like mayonnaise.	<500	<250	≥1.1	Total protein <2.5 gm/dl	Uncomplicated cirrhotic ascites (WBC can rise to >1000/cu.mm but is lymphocyte predominant and PMN <250 /cu.mm in absence of signs and symptoms of infection occurs  in diuresis related elevation)	Ultrasound &/or liver biopsy
					Total protein ≥2.5 gm/dl	Cardiac ascites	Chest X-ray and ECG
Bloody (>10,000 RBCs/cu.mm is pink; >20,000 is red; hetero-genous and clots immediately in traumatic tap; homo-genous and doesn’t clot because clot has already lysed in non-traumatic or remotely traumatic tap)	Subtract 1 WBC / 750 RBCs   Subtract 1 PMN / 250 RBCs			<1.1	Total protein <2.5 gm/dl	Nephrotic ascites	24 hour urine protein
		<500 or ≥500	≥250 (≥50% PMNs)	≥1.1	Single organism in culture, TP <1 gm/dl, Glucose >50 mg /dl, LDH <225 IU/L	SBP	Collect fluid for culture in blood culture bottles. Gram stain is positive only when >10,000 bacteria/ml. Clinical response to antibiotic
				≥1.1 or <1.1	Polymicrobial infection, TP >1 gm/dl, Glucose <50 mg/dl, LDH ≥225 IU/L	Secondary bacterial peritonitis	Look for perforation – Upright chest xray (gas under diaphragm); Contrast studies of GI tract
Milky	Triglyceride concentration >110 mg/dl is diagnostic of chylo-peritoneum; 100-200 mg/dl is like dilte skim milk; >200 mg/dl is like opaque milk			<1.1	Ascitic fluid amylase >100 U/L	Pancreatic ascites	Abdominal CT
			≥250 (<50% PMNs)	≥1.1	Positive cytology	Peritoneal carcinomatosis & portal hypertension	Search for primary tumor Serum AFP is more sensitive than peritoneal fluid cytology in HCC (rarely sheds cells in ascitic fluid).
Dark brown	Bilirubin concentration (> than serum in biliary perforation; < than serum in deeply jaundiced patients) Tea-colored in pancreatitis (Effect of pancreatic enzymes on RBC) Black in pancreatic necrosis and melanoma.				Fluid for TB testing	Tuberculous peritonitis and underlying cirrhosis	Myoco-bacterial growth on culture of laparoscopic biopsy specimen of peritoneum (100% sensitive) Culture of 50 ml ascitic fluid (50% sensitive) ADA >30 U/L (93% sensitive and specific) IFN-γ >3.2 U/ml (93% sensitive and 96% specific)
				<1.1	Positive cytology (nearly 100% sensitive)	Peritoneal carcinomatosis	Search for primary tumor
					Fluid for TB testing	Tubercular peritonitis	Myoco-bacterial growth on culture of laparoscopic biopsy specimen of peritoneum

Serum Ascites Albumin Gradient (SAAG)

SAAG = Serum Albumin Concentration – Ascitic fluid Albumin Concentration

• ≥1.1 gm/dl suggests portal hypertension (pre-hepatic, hepatic or post-hepatic)
• <1.1 gm/dl suggests portal hypertension to be unlikely.

HIGH GRADIENT≥1.1 g/dL (11 g/L)	LOW GRADIENT<1.1 g/dL (11 g/L)
Sinusoidal	Biliary ascites
Cirrhosis including SBP	Bowel obstruction or infarction
Acute Hepatitis or Hepatic failure	Nephrotic syndrome and hypoalbuminemic states
Extensive malignancy (HCC or metastases)	Pancreatic ascites
Post-sinusoidal	Peritoneal carcinomatosis
Right sided heart failure including constrictive pericarditis and Tricupsid regurgitation	Postoperative lymphatic leak
Budd-Chiari syndrome	Serositis in connective tissue diseases
	Tuberculous peritonitis
Sinusoidal obstruction syndrome	Meig’s syndrome (Ovarian fibroma)
Pre-sinusoidal: Portal or splenic vein thrombosis

Mixed Ascites:

• Portal hypertension from cirrhosis with another cause of ascites like tubercular peritonitis or peritoneal carcinomatosis.
• SAAG ≥1.1 gm/dl in such cases.

Points to remember:

• If SAAG is definitive: determine SAAG only on the 1st paracentesis specimen and donot repeat in subsequent paracentesis.
• If SAAG is borderline (1 or 1.1 gm/dl): analysis in subsequent paracentesis usually provides definitive result.
• Both serum and ascitic fluid sample must be obtained nearly simultaneously (on the same day, preferably within same hour).

Falsely low SAAG:

• Serum albumin <1.1 gm/dl
• Arterial hypotension (may result in decrease in protal pressure)
• Hyperglobulinemia (contribute to oncotic force)

Correction of SAAG for hyperglobulinemia:

Corrected SAAG = Uncorrected SAAG X 0.16 X (serum globulin in gm/dl + 2.5)

Falsely high SAAG:

• Chylous ascites (lipid interferes with the albumin assay)

Choleperitoneum following Biliary perforation

• Ascitic fluid bilirubin >6 mg/dl
• Ascitic fluid bilirubin to Serum bilirubin ration >1

Bacterial Peritonitis

In patients with Ascitic fluid ANC ≥250/cu.mm it is necessary to differentiate between Spontaenous Bacterial Peritonitis (SBP) and Secondary Bacterial Peritonitis (due to bowel perforation or intra-abodminal source of infection). 2 out of 3 criteria of the following must be met for diagnosis of secondary bacterial peritonitis:

1. Total protein
2. Glucose
3. LDH

Ascitic fluid tests	Early Spontaneous bacterial peritonitis	Secondary bacterial peritonitis
ANC	≥250/cu.mm	≥250/cu.mm
Total protein	<1 gm/dl	>1 gm/dl
Glucose	>50 gm/dl	<50 gm/dl
LDH	< upper limit of normal (<225 U/L)	> upper limit of normal (>225 U/L)
Culture	Monomicrobial	Polymicrobial

References:

1. Sleisenger and Fordtran’s Gastrointestinal and Liver Disease
2. Koss’ Diagnostic cytology and Its Histopathologic Bases
3. GI/Liver Secret Plus by Peter R McNally