D2.298 - Diagnostic performance of skin prick testing with fresh and frozen cow's milk in addition to commercial extract in cow’s milk allergy

In addition to standardized commercial extracts, prick-to-prick (PtP) tests with suspected food is common in clinical practice for diagnosing food allergy. Previously PtP tests with frozen fruits have been found to be consistent with fresh ones. However, there is a lack of evidence on the diagnostic performance of PtPs with fresh or frozen cow’s milk (CM).

In this prospective study we performed PtP tests with fresh (immediately upon opening the package) and frozen (frozen at-18°C, and thawed at room temperature on the test day) pasteurized CM (3 g protein/100 ml) and skin prick tests (SPT) with a commercial CM (cCM) extract (Alergopharma, Germany) in patients with suspected IgE-mediated CM allergy (CMA). After diagnostic evaluations, the correlation between tests, and the sensitivity, specificity, positive (PPV) and negative (NPV) predictive values, and the accuracy of the tests were calculated. Receiver operating characteristics (ROC) curve analysis for each test was performed to determine the diagnostic cut-off values indicated CMA.

A total of 217 children were included. A strong correlation was found between SPT with cCM and the PtP tests with fresh (r=+0.778, p<0.001) and frozen (r=+0.758, p<0.001). The correlation between fresh and frozen CM was strong (r=+0.891, p<0.001). The specificity of all tests was > 99%. The highest sensitivity (95.2%), NPV (98.3%) and accuracy (98.2%) belonged to the PtPs with frozen-CM. SPT with cCM extract had the lowest sensitivity (61.9%) but the highest PPV (100%). According to the ROC analysis, the area under the curve (AUC) was found to be 0.936 (95% CI:0.885–0.988, p<0.0001) for the cCM, 0.993 (95% CI:0.985–1.000, p<0.0001) for fresh-CM, and 0.994 (95% CI:0.986–1.000, p<0.0001) for frozen-CM. Additionally, the diagnostic cutoff value for the wheal diameter indicating true CMA with the highest sensitivity and specificity was found to be 2.25 mm for all allergens. 

Our results indicate that prick-to-prick tests with fresh and frozen pasteurized CM demonstrate high sensitivity, specificity, PPV, and NPV, along with a strong correlation between them. Consequently, frozen-CM seems to be an alternative to fresh one in addition to standardized commercial CM allergen for the diagnosis of CMA in children.