ORIGINAL ARTICLE COMPARISON OF THE POSSUM, P-POSSUM AND CR-POSSUM SCORING SYSTEMS AS PREDICTORS OF POSTOPERATIVE MORTALITY IN PATIENTS UNDERGOING MAJOR COLORECTAL SURGERY RYASH V ATHER,KAMRAN ZARGAR-SHOSHTARI,SAMUEL ADEGBOLA AND ANDREW G. HILL Department of Surgery, South Auckland Clinical School, University of Auckland, Auckland, New Zealand Background: Physiologic and operative severity score for the enumeration of mortality and morbidity (POSSUM), ‘Portsmouth’- physiologic and operative severity score for the enumeration of mortality and morbidity (P-POSSUM) and ‘Colorectal’-physiologic and operative severity score for the enumeration of mortality and morbidity (Cr-POSSUM) are three related scoring systems, which uses individual patient parameters to predict postoperative mortality. POSSUM overpredicts mortality in low-risk patients and underpredicts mortality in elderly and emergency patients. P-POSSUM was developed to compensate for these weaknesses. Cr- POSSUM was developed specifically for colorectal surgery. We aim to establish which of these scoring systems would be most useful in an Australasian context. Methods: Data were collected for 308 patients and predicted mortality risk values were generated using each of the three systems. The Mann–Whitney U-test was then carried out on the scores for each system. Receiver–operator characteristic curves were designed to determine the relative accuracy of each approach at discriminating between death and survival. Results: All three POSSUM scoring systems showed a statistically significant ability to predict postoperative mortality. Addition- ally, in each system there was a significant difference in the raw physiologic and operative severity scores between survivors and those who died. A risk-stratification model was applied to each set of data, showing a correlation between an increase in risk and an increase in mortality rate. Finally, the receiver–operator characteristic curves generated showed that in this study group POSSUM, P-POSSUM and Cr-POSSUM were all satisfactory predictive tools although the latter tended to be relatively less accurate. Conclusion: Physiologic and operative severity score for the enumeration of mortality and morbidity, P-POSSUM and Cr-POS- SUM are all reliable predictors of postoperative mortality in the Australasian context; although there was a trend towards POSSUM and P-POSSUM being better predictors than Cr-POSSUM. However, Cr-POSSUM requires fewer individual patient parameters to be calculated and is thus easier to generate. An ideal preoperative scoring system remains to be developed for predicting mortality in patients undergoing colorectal surgery. Key words: colorectal, Cr-POSSUM, mortality, POSSUM, P-POSSUM. Abbreviations: CI, confidence interval; Cr-POSSUM, colorectal-physiologic and operative severity score for the enumer- ation of mortality and morbidity; POSSUM, physiologic and operative severity score for the enumeration of mortality and morbidity; P-POSSUM, Portsmouth-physiologic and operative severity score for the enumeration of mortality and morbidity; ROC, receiver–operator characteristic curve. INTRODUCTION Physiologic and operative severity score for the enumeration of mortality and morbidity (POSSUM) is a predictive equation com- monly used to predict outcomes of surgery. 1 It uses several indi- vidual parameters to form a ‘physiologic score’ and an ‘operative severity score’, which is then used to generate a predicted value for mortality and morbidity. It has been shown that POSSUM tends to overestimate the probability of death in low-risk patients and underestimate mortality in elderly and emergency patients. 2–4 Thus, ‘Portsmouth’ physiologic and operative severity score for the enumeration of mortality and morbidity (P-POSSUM) was developed. 5 P-POSSUM uses the same scoring parameters as POSSUM and has largely replaced POSSUM as a risk predictor. A later study evaluated the use of P-POSSUM as a predictive tool in colorectal surgery, and it was shown that a newer, simpler and dedicated scoring system, ‘Colorectal’ physiologic and operative severity score for the enumeration of mortality and morbidity (Cr- POSSUM), was more accurate at predicting postoperative mor- tality. 4 It uses fewer variables and has a different scoring system. AIM Given the uncertainty of the performance of these scoring sys- tems, we wished to establish which one would be most useful in Australasia. This study is a retrospective analysis of patient R. Vather BHB; K. Zargar-Shoshtari MBChB; S. Adegbola; A. G. Hill MD, FRACS. Correspondence: Associate Professor Andrew G. Hill, Department of Sur- gery, South Auckland Clinical School, University of Auckland, Middlemore Hospital, PO Box 93311, Otahuhu, Auckland, 2024, New Zealand. Email: ahill@middlemore.co.nz Accepted for publication 7 May 2006. ANZ J. Surg. 2006; 76: 812–816 doi: 10.1111/j.1445-2197.2006.03875.x Ó 2006 Royal Australasian College of Surgeons