Alkaline phosphatase (ALP) is an enzyme present in intestinal mucosa, bile, bone and renal tubule cells. Bile acids have been shown to decrease ALP activity from bone and kidney but not those from intestinal origin. This action can be mimicked in serum and peritoneal fluid samples by the use of an L-phenylalanine buffer which specifically measures intestinal ALP activity only; while the standard buffer measures total ALP activity. We sought to assess the diagnostic and prognostic relationship of intestinal and total ALP activity between serum and peritoneal fluid in 126 horses with acute colic. Blood and peritoneal fluid samples were analyzed for ALP activity using both the standard and L-phenylalanine based buffers. Neither total nor intestinal serum ALP activity was useful in classifying type or severity of intestinal damage. Total and intestinal peritoneal fluid ALP activity were lowest in horses suffering simple medical colic and non-strangulated surgical lesions, and highest in surgical cases with suspected ulceration, strangulation, peritonitis and intestinal rupture. High total and intestinal peritoneal fluid ALP activity was associated with greater intestinal damage, increased probability of surgical intervention and a worse prognosis while low total and intestinal peritoneal fluid ALP activity was unable to accurately differentiate between simple medical colics and surgical colics. The use of L-phenylalanine buffer in both serum and peritoneal fluid did not improve the sensitivity of the test. Based on these results, determination of total ALP activity in peritoneal fluid may be helpful in identifying ischemic or inflammatory bowel lesions in horses with acute colic. A portable clinical analyzer (PCA) was used for the determination of venous blood and peritoneal fluid pH value, glucose, lactate and electrolyte concentrations in a hospital setting. Blood and peritoneal fluid glucose, lactate, sodium, chloride and potassium concentrations, and pH value were determined using both a portable clinical analyzer with test cartridges and an in-house analyzer in 56 horses with acute abdominal disease. Results were compared by the Bland-Altman method of comparison and linear regression. The PCA yielded higher blood and peritoneal pH values, with greater variability in the alkaline range and lower pH values in the acidic range. The PCA glucose concentrations (<150 mg/dL) were significantly lower, and were higher in the high range (>150 mg/dL). Venous lactate concentration (<5 mmol/dL) arid peritoneal fluid lactate concentration (<2 mmol/dL) had the smallest variability. On average, the PCA underestimated peritoneal lactate and glucose concentration. Peritoneal fluid sodium and chloride concentration had higher bias and variability than venous sodium and chloride concentration. Venous and peritoneal fluid potassium concentration was closely clustered around the mean with a low bias and variability. Correlation coefficients were >0.80 for all values except venous and peritoneal sodium concentration; venous chloride concentration and venous pH value. The PCA may be suitable for point-of-care biochemical analysis of blood and peritoneal fluid for horses suffering colic and may provide further diagnostic and prognostic information. The PCA may be of help in diagnosing metabolic acidosis, uroperitoneum, septic and non-septic peritonitis and intestinal ischemia. This may be of benefit to ambulatory equine clinicians. / Graduation date: 2004