112 Carl F. Ihler et al. Ta bl e 2 . Survivors and non-survivors of different diagnosis and treatment in 92 colic cases. Survivors (n) Non-survivors (n) % Survivors 1 For survivors: Clinical diagnosis. For non-survivors: Diagnosis based on necropsy. n = number of observations. Diagnosis1 Non-speciﬁc colic Large colon impaction Displacement large colon Strangulation small intestine Enterocolitis Peritonitis Total Treatment Medically treated cases Surgically treated cases 10 25 16 2 5 0 58 36 22 Plasma D-dimer values were assessed by the Nycomed NycoCard D-Dimer test (Axis- Shield PoC AS, Oslo, Norway) on citrated ve- nous plasma. The test is based on an immuno- ﬁltration of citrated plasma through a mem- brane attached with monoclonal antibody fol- lowed by colloidal gold-labelled monoclonal antibody staining (Gogstad et al. 1993). The in- tensity of colour was measured semi quantita- tively using a NycoCard Reader (Axis-Shield PoC AS, Oslo, Norway). In addition, the D- dimer test was used in 20 healthy horses as con- trols. Two cut-off values, 0.5 and 1.5 mg/l were tested in the statistical analysis. The different laboratory variables used in this study are presented in Table 1. All clinical variables and blood samples were obtained immediately after arrival at the hospi- tal according to a standard protocol. Further, clinical and laboratory variables obtained dur- ing the stay in hospital were used as the basis of further treatment of the patient and not used in the statistical analysis. Statistical methods Initially, survivors and non-survivors were compared with respect to year of inclusion Acta vet. scand. vol. 45 no. 1-2, 2004 1 4 9 10 3 7 34 10 24 91 86 64 17 63 0 63 78 48 (1997 or 1999), breed, age, gender and clinical and laboratory variables using Wilcoxon/ Kruskal Wallis Rank Sum Test for continuous variables and Fischer Exact Test for nominal or ordinal variables was performed using JMP for Windows version 4.02 (SAS Institute Inc, USA). Rectal ﬁndings were not used as a vari- able in the analysis because the variable was es- sential in the classiﬁcation of surgically and medically treated cases. To handle collinearity, a correlation analysis of the various explanatory variables was per- formed for surgically and medically treated cases separately. When variables showed strong correlation (Spearman þ >0.5) the variable with the lowest p-value in the univariable analyses was selected. These selected variables and the other variables showing p <0.15 in the univari- able analysis were used in a multivariable logis- tic model (Hosmer & Lemeshow 2000) to asso- ciate survival/non-survival with clinical an laboratory variables for surgically and medi- cally treated horses. The same procedure was also used for all cases to simulate a "ﬁeld situa- tion " where clinical variables and D-dimer, as a horse-side test, were the only available vari- ables.