Calculate the Serum-Ascites Albumin Gradient to differentiate portal hypertensive from non-portal ascites. Includes SBP screening, LDH analysis, and diagnostic algorithm.
The Serum-Ascites Albumin Gradient (SAAG) is the single most useful test for classifying the etiology of ascites. By subtracting the ascites albumin concentration from the serum albumin, SAAG directly reflects the portal-sinusoidal pressure gradient — the driving force behind portal hypertensive ascites.
A SAAG ≥ 1.1 g/dL identifies portal hypertension with 97% accuracy, replacing the older transudate/exudate classification which had significant overlap. This critical threshold divides ascites into two distinct pathophysiological categories: high-SAAG (portal hypertension from cirrhosis, cardiac failure, or hepatic vein obstruction) and low-SAAG (peritoneal disease from malignancy, tuberculosis, nephrotic syndrome, or pancreatitis).
This calculator extends basic SAAG with ascites fluid cell count analysis for spontaneous bacterial peritonitis (SBP) screening, LDH ratio for secondary peritonitis assessment, and a four-quadrant diagnostic algorithm combining SAAG with ascites total protein for refined differential diagnosis. SBP (ascites neutrophil count ≥ 250/µL) is a medical emergency requiring immediate antibiotics in cirrhotic patients. Check the example with realistic values before reporting.
Ascites has dozens of possible causes, and the clinical presentation alone is often insufficient for diagnosis. SAAG provides a single test that immediately narrows the differential into two categories with 97% accuracy — portal hypertensive vs. non-portal causes — directing the entire subsequent workup and treatment plan. Simultaneous SBP screening can be life-saving, as untreated SBP has 30–50% mortality.
SAAG = Serum Albumin (g/dL) − Ascites Albumin (g/dL) ≥ 1.1 g/dL = Portal hypertension (97% accuracy) < 1.1 g/dL = Non-portal causes Ascites ANC = WBC × (Neutrophil % / 100) SBP: ANC ≥ 250 cells/µL
Result: SAAG = 2.2 g/dL (High), Low protein → Portal hypertension (cirrhosis)
SAAG = 3.2 − 1.0 = 2.2 g/dL, well above the 1.1 threshold confirming portal hypertension. Ascites protein < 2.5 g/dL suggests cirrhosis as the cause rather than cardiac ascites (which typically has high ascites protein). This is the most common clinical scenario.
Use consistent units, verify assumptions, and document conversion standards for repeatable outcomes.
Most mistakes come from mixed standards, rounding too early, or misread labels. Recheck final values before use. ## Practical Notes
Use this for repeatability, keep assumptions explicit. ## Practical Notes
Track units and conversion paths before applying the result. ## Practical Notes
Use this note as a quick practical validation checkpoint. ## Practical Notes
Keep this guidance aligned to expected inputs. ## Practical Notes
Use as a sanity check against edge-case outputs. ## Practical Notes
Capture likely mistakes before publishing this value. ## Practical Notes
Document expected ranges when sharing results.
The old transudate/exudate classification (Light's criteria adapted from pleural fluid) misclassified 15–20% of ascites samples. SAAG has 97% accuracy for identifying portal hypertension because it directly reflects the portal pressure gradient, regardless of diuretic use or albumin infusions.
A SAAG ≥ 1.1 (portal hypertension) with ascites protein ≥ 2.5 g/dL suggests cardiac ascites (CHF, constrictive pericarditis) or acute Budd-Chiari syndrome. In cardiac ascites, the hepatic sinusoidal pressure is elevated by right heart failure rather than liver disease.
Suspect SBP in any cirrhotic patient with ascites who develops fever, abdominal pain, encephalopathy, renal deterioration, or unexplained clinical worsening. Diagnostic paracentesis should be performed before starting antibiotics. ANC ≥ 250/µL with positive culture confirms SBP.
Yes. Severe hypoalbuminemia (serum albumin < 1.0 g/dL) can compress the SAAG, making it falsely low even with portal hypertension. In such cases, clinical context and imaging (splenomegaly, varices) should guide diagnosis.
Routine: cell count with differential, albumin, total protein. If infection suspected: Gram stain, culture (inoculate blood culture bottles at bedside). If malignancy suspected: cytology, CEA, LDH. If TB suspected: AFB smear/culture, adenosine deaminase (ADA).
Diagnostic paracentesis should be performed at every hospital admission in cirrhotic patients with ascites, whenever infection is suspected, and when new symptoms develop. It is a safe procedure even with coagulopathy (do not transfuse platelets/FFP unless profoundly abnormal).