Serum-Ascites Albumin Gradient
A 54-year-old man with hepatitis C infection has progressive abdominal distension over six weeks. Examination shows spider naevi, splenomegaly, and shifting dullness. Diagnostic paracentesis is performed with a simultaneous blood sample. The ascitic albumin is 8 g/L, the serum albumin is 27 g/L, and the ascitic total protein is 12 g/L. How is the serum-ascites albumin gradient calculated and what does his value indicate?
- A.Ascitic albumin minus serum albumin; 19 g/L indicates peritoneal disease
- B.Serum albumin minus ascitic albumin; 19 g/L indicates portal hypertensionCorrect
- C.Serum albumin divided by ascitic albumin; ratio above 2 indicates malignancy
- D.Ascitic protein minus ascitic albumin; 4 g/L indicates cardiac ascites
Explanation
The serum-ascites albumin gradient is obtained by subtracting the ascitic fluid albumin from the serum albumin measured on the same day, giving 27 minus 8, that is 19 g/L in this patient. A gradient of 11 g/L or more indicates portal hypertension with about 97 percent accuracy, and it has replaced the older transudate versus exudate classification because it performs far better. The physiological basis is Starling forces: high portal hydrostatic pressure drives a relatively protein-poor ultrafiltrate into the peritoneal cavity, so the albumin difference between the two compartments remains wide. Causes of a high gradient include cirrhosis, alcoholic hepatitis, heart failure, constrictive pericarditis, Budd-Chiari syndrome, and massive hepatic metastases. A gradient below 11 g/L indicates ascites not driven by portal hypertension, such as peritoneal carcinomatosis, tuberculous peritonitis, pancreatic ascites, nephrotic syndrome, or serositis. Ascitic total protein then subdivides high-gradient ascites further: a value of 25 g/L or more suggests a cardiac cause or Budd-Chiari, whereas less than 25 g/L is typical of cirrhosis, as seen here. The polymorphonuclear count of 90 cells/mm3 is below the 250 threshold, so spontaneous bacterial peritonitis is excluded. Reversing the subtraction, taking a ratio, or using total protein alone are all incorrect approaches that would misclassify the ascites. Cell count, albumin, total protein, and culture in blood culture bottles at the bedside are the core tests on every diagnostic tap.
Why each option
- A.
- The subtraction is reversed; ascitic albumin is lower than serum albumin in portal hypertensive ascites, so this would yield a negative value.
- B.
- Correct. Serum albumin minus ascitic albumin gives 19 g/L, and any value of 11 g/L or above indicates portal hypertension.
- C.
- The gradient is a difference, not a ratio, and malignant ascites characteristically produces a low gradient below 11 g/L.
- D.
- Ascitic protein is used as a secondary test to separate cardiac from cirrhotic ascites, not as the gradient calculation itself.
Reference: AASLD 2021 Practice Guidance: Diagnosis, Evaluation, and Management of Ascites
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