Evaluation of the precision of intradermal injection of control substances for intradermal testing in clinically normal horses.
OBJECTIVE
To evaluate the precision of intradermal testing (IDT) in horses.


METHODS
12 healthy adult horses.


METHODS
IDT was performed on the neck of each horse by use of 2 positive control substances (histamine and phytohemagglutinin [PHA]) and a negative control substance. An equal volume (0.1 mL) for each injection was prepared to yield a total of 20 syringes ([4 concentrations of each positive control substance plus 1 negative control substance] times 2 positive control substances times 2 duplicative tests) for each side of the neck. Both sides of the neck were used for IDT; therefore, 40 syringes were prepared for each horse. Hair was clipped on both sides of the neck, and ID injections were performed. Diameter of the skin wheals was recorded 0.5, 4, and 24 hours after ID injection.


RESULTS
Intra- and interhorse skin reactions to ID injection of histamine and PHA resulted in wheals of uniform size at 0.5 and 4 hours, respectively. Significant intra- and interhorse variation was detected in wheals caused by PHA at 24 hours.


CONCLUSIONS
ID injection of histamine and PHA caused repeatable and precise results at 0.5 and 4 hours, respectively. Concentrations of 0.005 mg of histamine/mL and 0.1 mg of PHA/mL are recommended for use as positive control substances for IDT in horses. This information suggests that consistent wheal size is evident for ID injection of control substances, and variation in wheals in response to ID injection of test antigens results from a horse's immune response to specific antigens.
Wong
David M
DM
Department of Large Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic and State University, Blacksburg, VA 24061-0442, USA.
Buechner-Maxwell
Virginia A
VA
Manning
Thomas O
TO
Ward
Daniel L
DL
D000485:Allergens / Q000008:administration & dosage; D000818:Animals; D004306:Dose-Response Relationship, Immunologic; D005260:Female; D006632:Histamine / Q000008:administration & dosage*; D006736:Horses / Q000276:immunology*; D007271:Injections, Intradermal / Q000662:veterinary*; D007428:Intradermal Tests / Q000662:veterinary*; D008297:Male; D010835:Phytohemagglutinins / Q000008:administration & dosage*
D000485:Allergens; D010835:Phytohemagglutinins; D006632:Histamine