Fluid Analysis:- Part 4 – Ascitic fluid, Peritoneal tap, abdominal paracentesis, abdominal tap procedure

Ascitic fluid

Sample

• The ascitic fluid is aspirated from the peritoneal cavity.

Definition of ascitic fluid

The collection of fluid in the peritoneal cavity is called ascites and is called ascitic fluid.

Indications

1. An abdominal tap is done on the patient who has unexplained ascites.
2. An abdominal tap is done to relieve the intraabdominal pressure.
3. To diagnose whether ascites are benign or due to malignancy.
4. An abdominal tap is helpful to differentiate between the medical or surgical abdomen.
5. Abdominal fluid differentiates between Transudate or Exudate.
6. The abdominal fluid is removed for diagnostic and therapeutic purposes.

Pathophysiology of ascitic fluid

1. The peritoneal cavity is defined as the space between the visceral and parietal peritoneum.
2. The fluid is constantly produced by the peritoneal membrane and also reabsorbed by the same membrane where they contain a network of capillary and lymphatics.
3. If the secretion is increased or reabsorption is decreased that will lead to the collection of peritoneal fluid (Ascites).
4. The abdominal fluid is classified as Transudate when protein is less than 3 G /dl or Exudate when protein is more than 3 g/dl.
5. Transudate caused by congestive heart failure, cirrhosis, nephrotic syndrome, myxedema, hypoproteinemia, peritoneal dialysis, and acute glomerulonephritis.

Exudate is found more commonly in inflammation and malignancy. While some other conditions of drug hypersensitivity, pulmonary infarction, GIT diseases, and collagen diseases may form exudate.

Procedure for ascitic fluid tap:

1. This is an invasive procedure.
2. Ensure that the patient urinary bladder is empty.
3. The position is semi-prone and lateral.
4. Raise the bedhead side so that fluid accumulates in the lower abdomen.
5. First, sterilize the area. Clean the area with 70% isopropanol and allow it to dry the area.
6. If needed can give local anesthesia. Can raise the area with local anesthetic and make the small bleb. from where the needle can be inserted.
7. Locate the area with percussion where there is dullness indicating fluid.
   • Insert needle 5 cms superior and medial to the anterior superior iliac spine.
   • Or 2 cms below the umbilicus.
8. A needle 20 or 18 gauge is inserted into the abdominal cavity lateral to the umbilicus with constant negative pressure in the syringe, till you see the fluid.

Complications of ascitic fluid tap

1. There may be hypovolemia if a large volume of the ascitic fluid is aspirated.
2. There is a risk of peritonitis.

Normal features of ascitic fluid

Characteristics	Findings
Color	Clear and light yellow
Quantity	<50 ml
Red blood cells	Nil
White blood cells	<300/cmm
Glucose	70 to 100 mg/dL
Protein	<4.1 g/dL
Amylase	138 to 404 units/L
Alkaline phosphatase	Adult male = 90 to 240 units/L Adult female = 87 to 250 units/L
Lactate dehydrogenase (LDH)	Like serum  level
Microscopic examination	Cytology = no malignant cells No bacteria No fungal bodies
Carcinoembryonic antigen (CEA)	Negative

The Ascites, (peritoneal fluid) analysis includes:

1. Gross or physical appearance:
   1. Grossly peritoneal fluid is clear, and light yellow with <50 ml volume.
      1. No RBCs are seen.
      2. White blood cells are <300 /cmm
   2. Transudate fluid will be clear and straw color.
   3. Chylous color fluid: This is seen in blocked lymphatic vessels and the color is milky.
      1.  This may be seen in lymphoma, carcinoma, and tuberculosis.
      2. In such fluids, triglyceride value is > 110 mg/dl.
   4. The inflammatory condition gives rise to a turbid or opaque color. This may be seen in with peritonitis, pancreatitis, and appendicitis.
   5. The hemorrhagic color is due to trauma or intraabdominal bleeding, tumor infiltrates, or hemorrhagic pancreatitis.
   6. Greenish color or bile-stained fluid is seen in the ruptured gallbladder, acute pancreatitis, or in intestinal perforation.
   7. Bloody fluid may be due to:
      1. Traumatic tap.
      2. Hemorrhagic pancreatitis.
      3. Tumors.
      4. 10,000 RBCs/ µL will give pink color.
         1. 20,000 RBCs/ µL will give bloody appearance.
2. Specific gravity: Exudate has a specific gravity of more than 1.015 and less than 1.015 in transudate.
3. Proteins: Transudate has less than 3 g/dl and exudate has more than 3 g/dl of protein.
   1. The ratio of serum protein and ascitic fluid protein is more significant to differentiate exudate from transudate (Fluid protein/serum protein).
      1. A ratio of more than 0.5 is diagnostic of exudate.
   2. The albumin gradient between serum albumin and the ascitic fluid is also important to differentiate between exudate and transudate.
      1. Ascitic fluid albumin -(minus) serum albumin.
         1. A value 1.1 g/dL or more indicates transudate.
         2. Value <1.1 g/dL indicates exudate.
4. Total Cell Count: This depends upon the cause of ascites.
   1. In the inflammatory conditions count will be high and predominantly Polys are seen.
   2. In hemorrhagic conditions, the RBC count will be high.
5. Differential count: The inflammatory conditions show more polys and reactive mesothelial cells while transudate may show more lymphocytes. Malignant ascites also show more lymphocytes.
   1. RBCs presence indicates malignancies, tuberculosis, or intra-abdominal bleeding.
   2. WBCs presence indicates peritonitis, tuberculosis, or cirrhosis.
6. Cytology: This can be done better on cytospin and can differentiate the cells and as well find the malignant cells.
   1. Sometimes reactive mesothelial cells and malignant cell differentiation is difficult.
   2. Malignant cells have the variable morphology of the cells and nuclei. There is chromatin clumping and changed the nuclear/cytoplasmic ratio. May see prominent nucleoli.
7. Glucose: level may be done which usually equal to blood glucose level.
   1. But in tuberculous and bacterial ascites is low.
   2. It is low in peritoneal carcinomatosis.
8. Amylase: This will be raised in:
   1. Pancreatic trauma.
   2. Acute pancreatitis.
   3. Intestinal necrosis.
   4. Intestinal Perforation or strangulation.
   5. Pancreatic pseudocyst.
9. Lactate dehydrogenase, (LDH): This is diagnostic for exudate if the ascites LDH/serum LDH ratio is greater than 0.6.
10. The alkaline phosphatase level is greatly increased in infarction or the strangulation of the intestine.
11. Ammonia raised level is seen in:
    1. Ruptured or strangulated intestine.
    2. Ruptured appendix.
12. Gram stain: This may be performed but usually culture and sensitivity are advised.
13. Fungal infection usually is seen with histoplasmosis, candidiasis, or coccidioidomycosis.
14. Carcinoembryonic antigen is seen in the case of GIT malignancies.

Interpretation of ascitic fluid:

Physical appearance	Significance
Clear and pale yellow	Normal
Turbid	Bacterial infection
Bloodstained	Trauma, malignancy, or infection
Green	Gallbladder and pancreatic diseases
Milky	Lymphatic blockage and trauma
Biochemical findings
Amylase	Pancreatitis and gastrointestinal perforation
Glucose	Decreased in TB peritonitis and malignancy
Alkaline phosphatase	Increased in gastrointestinal perforation
CEA	In malignancy of the gastrointestinal system
CA 125	In ovarian malignancies
Blood urea nitrogen/creatinine	Ruptured and punctured urinary bladder
Microscopic findings
WBCs count  <500/cmm	Normal
>500/cmm	Bacterial peritonitis and cirrhosis
Gram stain and culture	Bacterial peritonitis
Acid-fast stain	TB peritonitis

Differentiation of exudate and transudate:

characteristics	Exudate	Transudate
appearance	cloudy/turbid	Clear / yellow
Total protein	> 3 G/dl	< 3 G/dl
ascitic protein/serum protein	> 0.5	< 0.5
Specific gravity	> 1.015	< 1.015
Cell differential	Neutrophils	mononuclear cells
Glucose	< 60 mg/dl	equal to serum
LDH ascites / LDH serum	> 0.6	< 0.6
Fibrinogen	Clots	No clots

• Note: Please see more details in fluid analysis part 2.

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