- Biochemical evaluation of the punctate:
- An exudate is characterized by:
- turbid, cell-rich fluid (Baltzer 2000)
- specific gravity > 1.016 g / l
- protein content > 2.5 g / dl (Herold 2022)
- Serum ascites albumin gradient = SAAG ≤ 11 g / l (Chub 2018) or 1.1 g / dl (Herold 2022).
- A transudate is characterized by:
- clear, cell-poor fluid (2000)
- specific gravity < 1,016 g / l
- protein content < 2.5 g / dl (Herold 2022)
- Serum ascites albumin gradient = SAAG ≥ 11 g / l (Chub 2018) or 1.1 g / dl (Herold 2022).
The sensitivity of the SAAG- value regarding the presence of portal hypertension is 96.7%, while for the liquid protein concentration, the distinction exudate / transudate was correct only in 55.6% of cases (Chub 2018).
Light- criteria:
The modified Light- criteria can also be used to determine whether ascites is an exudate or a transudate. The sensitivity is 97.9% and the specificity is 74.3% (Chub 2018).
- 1. fluid: plasma protein- ratio > 0.5
- 2. fluid: plasma LDH ratio > 0.6
- 3. LDH in ascites > 2/3 x upper reference limit for plasma LDL (Chub 2018).
If any of these 3 criteria are met, it is an exudate. In the original publication, sensitivity was 99% and specificity was 98% (Chub 2018).
In a study by Getnet et al (2019), the cause of ascites in transudate was shown to be more benign disease, whereas in exudate, malignancy was predominant.
- Spontaneous bacterial peritonitis (SBP):
Every punctate should always be examined for SBP. In SBP, the number of PMN (polymorphonuclear) - leukocytes is ≥ 500 x 106 / l (Kopcinovic 2014).
- Leukocyte-esterase strip test:
To enable a more rapid diagnosis of spontaneous bacterial peritonitis, a leukocyte esterase strip test should be performed in addition to microbiological tests. This is easy to perform and shows a high sensitivity between 64.7-100% and specificity between 99 -100% (Kopcinovic 2014). According to the 2018 guideline, the test strip was used to diagnose SBP in 1,041 patients in a recent multicenter study. This showed a significantly lower sensitivity of 45.3%, while the specificity was 99.2%. Hence, it is recommended to use the test strips only as a supplement to the usual diagnostic tests if no clinical chemistry laboratory is immediately available (Gerbes 2018).
In inflammatory ascites, granulocytes are additionally elevated and culture is positive (Wiest 2006).
Pancreatogenic ascites is characterized by an elevation of lipase (Herold 2022).
- is usually hemorrhagic
- contains cholesterol (Herold 2022) > 45 mg / dl (sensitivity approx. 80 %, specificity approx. 70 % [Wiest 2006])
- CEA in the predominant cases > 2.5 ng / ml (Braun 2018) (sensitivity about 45 %, specificity about 100 % [Wiest 2006])
- Ascites- total protein > 2.5 g / dl (sensitivity approx. 75 %, specificity approx. 70 %)
- Ascites / serum LDH > 1.0 (sensitivity approx. 60 %, specificity approx. 75 %)
- Cytology positive (sensitivity approx. 80 %, specificity approx. 100 %)
(Wiest 2006)
In chylous ascites, triglycerides are elevated to > 1,000 mg / dl (Braun 2018).