A study that will be published in the July issue of the Journal of Equine Veterinary Science has found that none of the currently available tests for equine lung allergic disease are helpful.
The study looked at 15 horses – 6 normal controls and 9 with varying degrees of equine “asthma” aka Heaves, RAO, equine COPD.
The testing methods evaluated were two different serum IgE antibody tests, intradermal skin testing and a functional in vitro test where blood is incubated with each suspected allergen then tested to see if the cells had released histamine. They also checked the horses’ sensitivity to inhaled histamine and to two different inhaled allergens.
The sensitivity to inhaled histamine was significantly greater in the horses with known lung disease than in the normal horses. It was the only testing method that could accurately differentiate between normal and affected horses. However, this test works by triggering respiratory distress and is not likely to be a popular diagnostic method. It was used in this study to confirm the clinical diagnoses as either normal or asthmatic.
The two blood tests for IgE antibodies are what most people are familiar with for allergy testing. There were just as many, if not more, positive reactions in the normal horses as in those with lung disease. The same thing happened with the functional in vitro testing. Intradermal skin testing, which is very reliable for skin reactions, also showed more positives in the normal horses and few in either group showed a skin reaction to mold – a known problem with lung disease. However, all horses except one in the asthma group showed a strong reaction to mosquito allergens.
In the inhaled allergens test, the horses were exposed to the substances which gave their highest test reaction on the functional in vitro test and also to another positive allergen selected from their test results. Two of the asthmatic horses had delayed reactions to the first test but none reacted on the second test.
The authors concluded: “In this study, no agreement was found between the results of four different, commercially available allergy tests for equine asthma. None of the four allergy tests could differentiate reliably between healthy and asthma-affected horses”.
Part of the problem is that both the antibody tests and the functional in vitro test are focusing on IgE, the antibody of immediate type allergic reactions, like what happens with extreme peanut allergies on your first bite. There is quite a bit of evidence that equine allergic lung disease is of the delayed reaction type. Another problem is that antibodies only mean the horse has been exposed to something. They cannot predict allergic reactions.
The bottom line is that, as with as with food allergies https://wp.me/p2WBdh-15k , blood tests cannot be used to identify what may be triggering your horse’s reactions. Save your money. Even more important, avoid the angst that comes with staring at a long list of “positive” test results which don’t mean anything.
Eleanor Kellon, VMD