Clinical review: scoring systems in the critically ill.

General illness severity scores are widely used in the ICU to predict outcome, characterize disease severity and degree of organ dysfunction, and assess resource use. In this article we review the most commonly used scoring systems in each of these three groups. We examine the history of the development of the initial major systems in each group, discuss the construction of subsequent versions, and, when available, provide recent comparative data regarding their performance. Importantly, the different types of scores should be seen as complementary, rather than competitive and mutually exclusive. It is possible that their combined use could provide a more accurate indication of disease severity and prognosis. All these scoring systems will need to be updated with time as ICU populations change and new diagnostic, therapeutic and prognostic techniques become available.