Prognostic indicators in colic horses 117 outcome. Recurrent pain despite analgesics or NSAIDs was, however, one of the criteria for surgery, and since surgically treated cases in the present study had a higher mortality, pain might indirectly relate to the outcome. Thoefner et al. (2000) found that a temperature deviation from 38 °C was a signiﬁcant variable in the multivariable logistic regression model expressing the outcome of a colic case. In the present study we did not ﬁnd such a relationship when temperature deviation from 38 °C was in- cluded in the model. Heart rate and the presence of abnormal mu- cous membranes were the only statistically sig- niﬁcant variables in the multivariate model for surgical cases. Even if the initial laboratory variables did not directly relate to the outcome, they were of importance in the decision making of supportive therapy such as ﬂuid therapy and correction of acid-base disturbances. In this way they might indirectly inﬂuence the out- come. The classiﬁcation of the mucous membranes was based on presence of hyperaemia and cyanosis. Since pallor or jaundice was not recorded in any horse in this study the authors chose a dichotomous classiﬁcation (normal/ab- normal) for mucous membranes. In medical cases PCV was the only explanatory variable in the ﬁnal logistic model. Also PCV represents a variable expressing the cardiovas- cular status in the patient. The ﬁnal models gave an excellent ﬁt by an area under the ROC curve of 0.94 in surgically and 0.88 in medically treated cases, respectively. The ROC curve plots the probability of deﬂect- ing a true signal (sensitivity) and a false signal (speciﬁcity) for the entire range of possible out- points. While the ROC curve assess the overall performance of the model, the prediction curves in Fig. 1 give the magnitude of the prob- ability of death given various levels of the pre- dictor variables. In the simulated "ﬁeld" situation, where only clinical variables and D-dimer were used, the only reliable predictors for survival were heart rate and the presence of abnormal mucous membranes. The D-dimer values did not give any additional information in explaining the outcome. This is in agreement with Thoefner et al. (2000). Sandholm et al. (1995), however, found that D-dimer was included in the ﬁnal lo- gistic model together with the variables heart rate and chloride. The reason for this might be that Sandholm et al. (1995) did not use other clinical variables than heart rate and respiratory rate in their statistical procedure. D-dimer, as the condition of the mucous membranes, is an indicator of cardiovascular status. During our logistic regressions D-dimer was excluded from the ﬁnal model. This supports that the evaluation cardiovascular variables as the mu- cous membrane in addition to heart rate tell more about the outcome than the D-dimer value. In conclusion, traditional clinical variables as heart rate and presence of abnormal mucous membranes in surgical and PCV in medical colic cases were the signiﬁcant predictors for the outcome. The other variables were, how- ever, important in establishing supportive treat- ment of the patients. References Blikslager AT, Roberts MC: Accuracy of clinicians in predicting site and type of lesion as well as out- come in horses with colic. J. Am. Vet. Med. As- soc., 1995, 207, 1444-1447. Ebert R: Lätalitätsaspekte der Kolikk des Pferdes. (Mortobily in colic hourses). Pferdheilkunde, 1994, 10, 97-101. Furr MO, Lessard P, White NA: Development of a colic severity score for predicting the outcome of equine colic. Vet. Surg., 1995, 24, 97-101. Gogstad GO, Dale S, Brosstad F, Brandnes Ø, Holtlund J, Gartner E, Borch SM: Assay of D- dimer based on immunoﬁltration and staining with gold colloids. Clin. Chem., 1993, 39, 2070- 2076. Acta vet. scand. vol. 45 no. 1-2, 2004