Normal Range of Albumin in Ascitic Fluid and Diagnostic Implications
The normal range of albumin in ascitic fluid is not a fixed value, but rather its clinical utility is in calculating the serum-ascites albumin gradient (SAAG), where a value ≥1.1 g/dL indicates portal hypertension with approximately 97% accuracy. 1
Understanding SAAG and Ascitic Fluid Albumin
The serum-ascites albumin gradient (SAAG) is calculated by:
- Measuring serum albumin and ascitic fluid albumin concentrations from specimens obtained on the same day
- Subtracting the ascitic fluid albumin value from the serum albumin value 1
This gradient has replaced the older exudate-transudate classification system because:
- SAAG has a diagnostic accuracy of 98% compared to only 52-80% for traditional markers 2
- It reliably distinguishes between portal hypertension-related and non-portal hypertension-related causes of ascites 3
Diagnostic Value of SAAG
High SAAG (≥1.1 g/dL)
Indicates portal hypertension-related ascites, such as:
- Liver cirrhosis
- Cardiac ascites
- Hepatic vein thrombosis (Budd-Chiari syndrome)
- Sinusoidal obstruction syndrome
- Massive liver metastases 1
Low SAAG (<1.1 g/dL)
Suggests non-portal hypertensive causes of ascites, such as:
- Peritoneal carcinomatosis
- Tuberculous peritonitis
- Secondary bacterial peritonitis 2
Additional Diagnostic Parameters
The combination of SAAG and ascitic fluid total protein levels provides enhanced diagnostic value:
| Parameter | Cardiac Ascites | Cirrhotic Ascites |
|---|---|---|
| SAAG | ≥1.1 g/dL | ≥1.1 g/dL |
| Total Protein | >2.5 g/dL | Generally <2.5 g/dL |
This combination helps differentiate between cardiac and cirrhotic causes of portal hypertension:
- In cardiac ascites, all patients had ascitic fluid total protein ≥2.5 g/dL 4
- In cirrhotic ascites, only 10% of patients had ascitic fluid total protein ≥2.5 g/dL 4
Clinical Application
When evaluating ascites:
- Perform diagnostic paracentesis to obtain ascitic fluid
- Measure both serum and ascitic fluid albumin on the same day
- Calculate the SAAG
- Measure total protein in ascitic fluid
- Use these values to determine the likely etiology of ascites
Common Pitfalls and Caveats
- Specimens for serum and ascitic fluid albumin must be collected on the same day for accurate SAAG calculation 1
- The presence of infection (spontaneous bacterial peritonitis) does not significantly affect the diagnostic accuracy of SAAG (89% accuracy in infected ascites) 2
- Relying solely on ascitic fluid albumin without calculating SAAG has limited diagnostic value
- The older transudate-exudate classification system is less accurate and should not be used 5
By using SAAG as the primary diagnostic tool for ascites, clinicians can more accurately determine the underlying cause and implement appropriate treatment strategies.