Serial prognostic score indexes in acute renal failure (ARF): best performance of scores obtained at the time of referral to the nephrologist

The APACHE-II score has been validated for the time of admission at the ICU, but has been widely used in outcome studies of patients with ARF, and frequently obtained at the time of indication of dialysis. Another prognostic score index - the ATN-ISS - obtained at the time of referral to the nephrologist, seems to have a better performance than the APACHE-II score. We sought to investigate whether the time of collection of data for APACHE-II could influence its prognostic value, and to compare it with the more specific ATN-ISS score. In a historical prospective study, we collected data from 205 ARF patients at the Hospital São Paulo - a university-based, not-for-profit, tertiary hospital - between February 1997 and November 1997. APACHE-II scores were calculated at the time of hospital admission (AP-1), time of referral for the nephrologist (AP-2) and day of the first dialysis (AP3). The ATN-ISS score was also obtained at the time of referral to the nephrologist. There were 98 males and 107 females, with a mean age of 52 ± 18 years; 70 patients (34%) required dialysis and 68 patients (33%) were admitted to the ICU. The overall mortality rate was 46%. Nonsurvivors had higher AP1 (19.6 ± 8.7 versus 15.4 ± 6.0; P < 0.001), AP2 (23.4 ± 7.2 versus 16.7 ± 5.3; P < 0.001) and AP3 (25.8 ± 6.24 versus 20.3 ± 3.9; P < 0.001). ATN-ISS was also higher for nonsurvivors (0.81 ± 0.17 versus 0.26 ± 0.15; P < 0.001). The area under the receiver operator curve (AUC) was obtained for each score. The AUC was lower for AP1 than for AP2 (0.64 versus 0.76; P < 0.001). However, the AUC for AP2 was similar to the AUC for AP3 (0.78 and 0.77, respectively; P = 0.75). The ATN-ISS was a better predictor than AP2 (0.97 versus 0.76; P < 0.001). The better performance of scores at the time of referral to the nephrologist than scores obtained at the admission or at the day of first dialysis suggests that ARF per se may be an important determinant of prognosis.