Association between prevalent care process measures and facility-specific mortality rates

Background. Medical communities often develop practice guidelines recommend ing certain care processes intended to promote better clinical outcome amon g patients. Conformance with those guidelines by facilities is then monitor ed to evaluate care quality, presuming that the process is associated with and can be used reliably to predict clinical outcome. Outcome is often moni tored as a facility-specific mortality rate (SMR) standardized to the mix o f patients treated, also presuming that inferior outcome implies a suboptim al process. The U.S. Health Care Financing Administration monitors three pr actice guidelines, called Core Indicators, in dialysis facilities to assist management of its end-stage renal disease program: (1) patients' hematocri t values should exceed 30 vol%, (2) the urea reduction ratio (URR) during d ialysis should equal or exceed 65%, and (3) patients' serum albumin concent rations should equal or exceed 3.5 g/dL. Methods. The associations of a facility-specific SMR were evaluated with th e fractions of hemodialysis patients not conforming to (that is, at varianc e with) the Core Indicators during three successive years (1993 to 1995) in large numbers of facilities (394, 450, and 498) using one-variable and mul tivariable statistical models. Three related strategies were used. First, t he association of the SMR with the fraction of patients not meeting the gui deline was evaluated. Second, each facility was classified by whether its S MR exceeded the 80% confidence interval above 1.0 (worse than 1.0, Group 3) , was less than the interval below 1.0 (better than 1.0, Group 1), or was w ithin the interval (Group 2). The fraction of those patients who did not me et the Indicator guidelines was then evaluated in each group. Third, the ab ility of variance from Indicator guidelines to predict into which of the th ree SMR groups a facility would be categorized was evaluated. Results. SMR was directly correlated with variance from the Indicator guide lines, but the strengths of the associations were weak particularly for the hematocrit (R-2 = 2.2%, 5.6, and 2.2 for each of the 3 years) and URR Indi cators (R-2 = 2.6, 0.6, 3.3). It was stronger for the albumin Indicator (R- 2 = 11.6, 20.4, 21.8). The fractions of patients falling outside of the Ind icator guidelines tended to be higher in the highest SMR group. The groups were not well separated, however, particularly for the hematocrit and URR I ndicators, and there was substantial overlap between them. Finally, althoug h the likelihood that a facility would be a member of the high or low SMR g roup was associated with fractional variance from Core Indicator guidelines , the strengths of association were weak, and the probability that a facili ty would be a member of the high or low group could not be easily distingui shed from the probability that it would be a member of the middle group. Conclusions. While there were statistical associations between SMR and the fraction of patients in facilities who were at variance with these guidelin es, they were weak and variances from the guidelines could not be used reli ably to predict high or low SMR. Such findings do not imply that measures r eflecting anemia, dialysis dose, or medical processes that influence serum albumin concentration are irrelevant to the quality of care. They do sugges t, however, that more attention needs be paid to these and other associates and causes of mortality among dialysis patients when developing care proce ss indicator guidelines.