In patients with cirrhosis and a low pretest probability for non-portal hypertension-related ascites, a low SAAG has a poor predictive value.
Often, when the SAAG is repeated in these patients, it will return to a level >1.1!
In other words, many patients with cirrhosis and a low SAAG do not actually have a second reason besides portal hypertension for their ascites. In a 2009 study of patients with cirrhosis and a low SAAG, Khandwalla et al. found that only a minority of these patients had a second cause (most commonly peritonitis or peritoneal carcinomatosis).
As such, the recommendation is to evaluate the other usual peritoneal fluid studies (e.g. cell count/diff, protein, cytology). If there is no clear secondary cause, it is reasonable to repeat the paracentesis – the aforementioned study found that on repeat testing, the SAAG often returned to the expected level >1.1!
Khandwalla et al. The utility of evaluating low serum albumin gradient ascites in patients with cirrhosis. Am J Gastroenterol. 2009;104:1401-1405.