Lactate, the ionized form of lactic acid, which is a byproduct of anaerobic metabolism, can provide objective insight into the prognoses of equine patients, according to Robert Franklin, DVM, Dipl. ACVIM, of the Equine Medical Center in Ocala, Fla. Franklin presented on this topic at the 2006 AAEP Convention.

Franklin said lactate tests are good, cheap, objective, and readily available tests for perfusion (the passage of fluid through the vessels of an organ) and tissue oxygenation. Horses with high lactate levels are more likely to require hospitalization and less likely to survive.

“How many times are we forced to make tough decisions and steer people in the right direction? Here’s data that can help steer you in the right direction,” Franklin said. “It helps me every day.”

L-Lactate is formed in muscles, red blood cells, the brain, and gut. Healthy adult horses typically have a lactate level of under 2 mmol/l, and healthy foals measure less than 3.5 at birth, and 2.5 during their first week.

Reasons for increased lactate include impaired tissue oxygenation (caused by pulmonary or circulatory problems, intense exercise, or anemia), drugs, endotoxins, hepatic (liver) failure, hyperglycemia, or malignancy (some tumors form intense amounts of lactate). Patients with high lactate levels that fail to return to normal, or normalize very slowly in spite of appropriate therapy, have a poor outcome.

Franklin said a study performed in humans entering an emergency room showed circulating lactate concentrations greater than 4 mmol/l were 98.2% specific in predicting the need for hospitalization.

Franklin said past horse case studies revealed that colic cases seen on the farm that had lactate levels below 2 rarely needed referral. Levels greater than 3 suggested a need for referral, and levels above 6 were generally associated with a poor outcome.

Franklin said a first lactate sample on a horse can reveal the severity of the horse’s condition, and subsequent draws can give insight into the horse’s prognosis. The test result can give a good indication when to start and stop particular therapies, when to refer the horse, and when to give up, according to Franklin.

A lactate test can be performed in 60 seconds. The machine that processes tests costs about $250. Lactate is measurable in any fluid, including venous and arterial blood, joint fluid, abdominal fluid, and cerebrospinal fluid.

“Anytime you’re going to measure a fluid, measure a lactate,” he said. Franklin encouraged other practitioners to test lactate and keep track of the results correlated to the outcome of cases in order to collect more data on its application in equine medicine.

“This may be the best predictor of outcome we have at our disposal,” Franklin said.

Get research and health news from the American Association of Equine Practitioners 2006 Convention in The Horse’s AAEP 2006 Wrap-Up sponsored by OCD Equine. Files are available as free PDF downloads