Investigations Required In Patients With Ascites

Ascites is defined as collection of excess free fluid in the peritoneal cavity and it could be due to a number of different medical conditions. A proper history and clinical examination may reveal the underlying cause but still certain general and specific investigation are to be carried out in order to confirm or find out the possible etiology.

General Investigations

1. Urine Dipstick: It is a simple and cheap procedure that will be strongly positive for protein in nephrotic syndrome. If so, a 24 hour urine collection for protein should be undertaken; more than 3.5gm is indicative of nephrotic syndrome.

2. Complete Blood Count: Raised white cell count may indicate an infective etiology but a differential white count is more specific.

3. Urea and Electrolytes: Elevated urea and creatinine may indicate a renal etiology; however , it may also be a component of hepatorenal syndrome, which is renal impairment secondary to liver failure.

4. LFT’s : May be deranged in the presence of liver disease. The serum albumin will be able to indicate hypoalbuminaemia but the underlying cause must still be sought.

5. Chest X-ray: Findings suggestive of cardiac failure are cardiomegaly, upper venous diversion of blood, the presence of Kerley B lines, pulmonary edema and pleural effusion. Occasionally the presence of carcinoma may be suggested by a mass in the lung.

6. Ultrasound Abdomen: In addition to confirming the presence of ascites ultrasound will detect any intra abdominal masses that are not palpable on clinical examination. It may also indicate the presence of fatty deposits in the liver in the presence of cirrhosis. Dilated collateral veins may be visualized in conditions that cause obstruction of the venous outflow of the liver, including cirrhosis and Budd-Chiari syndrome.

7. Abdominal Paracentesis: Aspiration of the ascitic fluid is very useful to help determine the underlying cause. A sample should be sent to microbiology clinical chemistry and pathology.

Ascitic fluid Examinations

Appearance

• Chylous The milky white appearance of chylous ascites is due to obstruction of the lymphatic ducts.
• Bile stained is suggestive of bile peritonitis
• Haemorrhagic can occur in malignancy, trauma and tuberculosis.
• Straw-coloured is the usual appearance with most other causes.

Biochemistry

1. Protein: The ascitic protein levels are often used to classifly the ascites as a transudate or an exudate; however this may not always be reliable. A transudate would be ascitic fluid with the protein concentration of less than 25 gm/l in the sample or 11 gm/l lower than the serum protein level, while an exudate is the opposite.
2. Amylase: is usually elevated in pancreatic ascites
3. Glucose: is low in bacterial infections
4. Triglyceride: it is elevated in chyl;ous ascites and may indicate obstruction of drainage of the thoracic duct.
5. Billirubin: it is elevated in bile ascites

Microbiology

• Gram and Ziehl-Neelsen staining with cultures may be positive with a bacterial etiology.

Cytology

• Neutrophilia is suggestive of a bacterial peritonitis,
• Tuberculous peritonitis usually results in a lymphocytosis. 
• Malignant cells may be identified and a primary source may be possible located.

Specific Investigations
1. Echocardiography: It will reveal most of the cardiac causes. Cardiac failure will manifest as poorly contractile ventricle with a reduced ejection fraction. A pericardial effusion is visible as an echo free space between the left ventricle and the pericardium.

2. Liver biopsy: will be able to confirm and may be able to ascertain the underlying cause of liver cirrhosis.

3. Renal Biopsy: reveals the underlying cause of nephrotic syndrome.

4. Portal venography: will be indicated if obstruction to the venous outflow of the liver is suspected and can be used to confirm Budd-Chiari syndrome and veno occlusive disease.