IgG anti-betalactoglobulin (betalactotest): its usefulness in the diagnosis of cow's milk allergy.

The aim of this prospective study was to evaluate the distribution of serum values of IgG anti-betalactoglobulin in 3 groups of subjects: a) 218 healthy subjects (138 M, 80 F) with age ranging from 1 month to 6 years; b) 205 patients with cow's milk protein allergy (CMPA) (130 M, 75 F) aged between 1 month and 4 years; c) 96 patients (50 M, 46 F) with symptoms compatible with CMPA, but suffering from other diseases (age range 1 month-6 years). The IgG anti-betalactoglobulin values were obtained using a new commercially available immunoenzymatic method. There was a marked difference in the distribution of IgG antibetalactoglobulin values in the 3 study groups. In healthy controls the value corresponding to the 5th centile was 5%, to the 50th centile 17%, to the 90th centile 48%. In the gastroenterological controls, 5th centile was 5%, 50th centile 15% and 90th centile was 56%. In the patients with CMPA, 5th centile was 27%, 50th centile 101% and 90th was 147%. The distribution of the values was therefore significantly different in the CMPA group from that of the other 2 groups (p < 0.0001). Plotting receiver operating characteristics curves, we have indicated a betalactotest value of 36% as a cut-off with the highest diagnostic accuracy (89% sensitivity, 85% specificity). We suggest that the betalactotest should be used to confirm diagnosis in patients with suspected CMPA; with a cut-off of over 48% we found only one false positive for diagnosis of CMPA in patients presenting other diseases with an identical clinical picture.