The criterion for point assignment is that a certain breakpoint be met at anytime during that 48 hour period, so that in some situations it can be calculated shortly after admission. It is applicable to non-gallstone pancreatitis.
For gallstone pancreatitis, the parameters are:
Substantial pancreatic necrosis (at least 30% glandular necrosis according to contrast-enhanced CT)
If the score ≥ 3, severe pancreatitis likely.
If the score < 3, severe pancreatitis is unlikely
Score 0 to 2 : 2% mortality
Score 3 to 4 : 15% mortality
Score 5 to 6 : 40% mortality
Score 7 to 8 : 100% mortality
^Ranson JH, Rifkind KM, Roses DF, Fink SD, Eng K, Spencer FC (1974). "Prognostic signs and the role of operative management in acute pancreatitis". Surgery, Gynecology & Obstetrics139 (1): 69–81. PMID4834279.