BACKGROUND AND AIM: Skin prick test (SPT) with a wheal diameter of >3 mm, 
generally accepted as a positive, is most commonly use diagnostic tool for 
Allergic rhinitis. Aim was to validate wheal size of Skin Prick Test for the 
Bermuda grass, in desert environment, with positive Bermuda grass Nasal 
challenge in same environment.
METHODS: In 53 adults, mean age 33.43 ± 9.36 years, both gender (females: 
33.96%), SPT positive on Bermuda grass with cut off wheal longest diameter of 3 
mm, Bermuda grass nasal challenge test (bgNCT) was carried out. Response was 
assessed subjectively (scored) and objectively (PNIF). Safety profile was 
assessed by PEF measurement.
RESULTS: Mean weal size of SPT (mm) was bigger in bgNCT positive patients (n=47; 
88.68%) 8 [4, 15] vs 5 [3, 6] (p<0.0001). ROC analysis showed Bermuda Grass SPT 
at the threshold of >6.5mm enabled identification of Bermuda challenge with 
sensitivity of 82.98% and specificity of 100.0% (area under the curve 0.9326, 
standard error 0.03528; 95% confidence interval (CI): 0.8635 to 1.002; 
p=0.0006203).
CONCLUSIONS: A SPT wheal size ≥6.5mm  might be considered as an appropriate 
wheal size for confirming Bermuda grass allergy in adults with SAR, avoiding the 
demanding, time consuming and often unavailable bgNCT, especially in patients 
eligible for allergen immunotherapy. In these patients, bgNCT is recommended if 
SPT wheal size is <6.5 mm.