Acute-phase proteins as diagnostic markers in horses with colic.

OBJECTIVE To investigate the diagnostic potential of the concentrations of acute-phase proteins serum amyloid A (SAA), haptoglobin (Hp), and fibrinogen in blood and peritoneal fluid (PF) for differentiating horses with inflammatory colic (entero-colitis and peritonitis) from those with surgical colic. DESIGN Prospective observational multicenter study. SETTING Two university referral hospitals. ANIMALS Horses referred for severe acute abdominal pain to Hospital 1 (n = 148) or Hospital 2 (n = 78). INTERVENTION Blood and PF samples collected at admission were used for acute-phase protein concentration measurement. MEASUREMENTS AND MAIN RESULTS A multivariable logistic model including clinical parameters (lethargy, rectal temperature >38°C [100.4°F], normal rectal examination findings, and gastric reflux of 5-10 L) recorded at admission was constructed from Hospital 1 data. The ability of the model to correctly differentiate inflammatory from surgical colic was 86% determined as area under the receiver operating characteristic curve. Adding blood parameters (WBC, PCV, total plasma protein, lactate, SAA, Hp, and fibrinogen concentrations) to the logistic model based on clinical parameters revealed that only WBC and SAA and fibrinogen concentrations improved the model. With SAA included in the model no additional blood parameters improved the model, and the final model had an area under the curve of 90%. Addition of PF parameters (hemolysis, total protein concentration, WBC, SAA, or Hp concentrations) did not improve the model. When validated in Hospital 2 data, the models had good integrity and diagnostic performance. CONCLUSIONS Evaluation of SAA in serum improved the ability to differentiate horses with acute inflammatory colic requiring medical treatment from horses with colic requiring surgery, as it allowed an additional 4% of horses to be correctly classified into medical and surgical cases. Improved differentiation of these 2 groups of horses with colic may minimize the risk of unnecessary or delayed surgery.