Normal Albumin-Globulin Ratio
The normal albumin-to-globulin (A/G) ratio is typically 1.0 to 2.5, with most healthy individuals falling between 1.2 and 2.2, though this specific ratio is not routinely used in the diagnosis of tuberculous peritonitis where the serum-ascites albumin gradient (SAAG) and absolute albumin levels are more clinically relevant.
Understanding the A/G Ratio in Clinical Context
The albumin-to-globulin ratio is calculated by dividing serum albumin by serum globulin (total protein minus albumin). While this ratio exists as a laboratory value, it has limited utility in the specific context of tuberculous peritonitis compared to other parameters.
Normal Albumin Values
- Standard threshold: Serum albumin <3.5 g/dL (35 g/L) defines hypoalbuminemia in most clinical contexts 1
- Optimal target: The National Kidney Foundation suggests albumin ≥4.0 g/dL represents the lower limit of normal range 1
- Laboratory variation: Normal albumin concentrations vary by laboratory methodology (typically 3.5-5.0 g/dL with bromcresol green method), so local reference ranges should be consulted 2, 1
Critical Consideration in Tuberculous Peritonitis
In patients with suspected tuberculous peritonitis, the A/G ratio itself is not the diagnostic parameter of choice. Instead, focus on:
Serum-Ascites Albumin Gradient (SAAG)
- SAAG <11 g/L (1.1 g/dL) is characteristic of tuberculous peritonitis 3, 4
- All patients with tuberculous peritonitis without chronic liver disease had SAAG <11 g/L in controlled studies 3
- This low gradient distinguishes tuberculous peritonitis from portal hypertension-related ascites 4
Ascitic Fluid Characteristics
- Ascitic fluid protein >25 g/L has 100% sensitivity in tuberculous peritonitis without liver disease 3
- Ascitic fluid LDH >90 U/L shows 100% sensitivity in patients without chronic liver disease and 84% with coexistent liver disease 3
- Lymphocyte predominance with low albumin gradient occurs in all tuberculous peritonitis cases 5
Severe Hypoalbuminemia in Tuberculous Peritonitis
When severe hypoalbuminemia is present:
Diagnostic Implications
- Hypoalbuminemia is common in tuberculous peritonitis and represents both the inflammatory nature of the disease and potential malnutrition 6
- Baseline hypoalbuminemia is an independent risk factor for atypical presentations of tuberculous disease 6
- Albumin <3.0 g/dL carries particularly high risk for complications and poor outcomes 1
Important Caveats
- Hypoalbuminemia does not necessarily indicate protein-energy malnutrition alone, as albumin is a negative acute-phase reactant that decreases during inflammation and infection 1
- Measuring inflammatory markers like C-reactive protein can help distinguish inflammation-driven hypoalbuminemia from pure malnutrition 1
- In tuberculous peritonitis with coexistent chronic liver disease, ascitic fluid protein may be lower (70% had >25 g/L vs 100% without liver disease) and SAAG may be higher (52% had >11 g/L), making diagnosis more challenging 3
Clinical Algorithm for Suspected Tuberculous Peritonitis
- Measure SAAG first: SAAG <11 g/L strongly suggests tuberculous peritonitis over cirrhotic ascites 3, 4
- Check ascitic fluid protein: >25 g/L supports tuberculous peritonitis 3
- Assess ascitic fluid LDH: >90 U/L is highly sensitive, especially useful when liver disease coexists 3
- Confirm with laparoscopy: Peritoneal biopsy with M. tuberculosis culture provides definitive diagnosis (63% positive culture rate) 3
- Consider adenosine deaminase (ADA): Median ADA level of 139 U/L in tuberculous peritonitis serves as a sufficient, safe, and inexpensive diagnostic method 5
The A/G ratio itself provides minimal additional diagnostic value in this clinical scenario compared to these more specific parameters.