Interasma Regional Meeting
Marrakech, 27-30 November 2003
Evaluation of a new in vitro test (IAST®) for the screening of allergy in asthmatic patients
A. Papaconstantinou, A. Makrygianni, U. Spyrakou
Medical Diagnostic Laboratories (Athens)
Purpose of the study: The clinical evaluation of a new in vitro screening test for the diagnosis of respiratory allergy in asthmatic patients.
Patients and methods: 290 unselected adult and paediatric patients with asthma were studied (118 males and 172 females) aged 1 to 84 years (mean: 35,1 years). The diagnosis of asthma was based on history, clinical examination and (in persons able to perform) lung function tests.
Skin prick tests were performed in 286 patients with the standard set of Anallergo (Florence, Italy). Any reaction with a wheal being ≥ 5 mm in diameter after 20 minutes was counted as positive.
Specific IgE determinations for 15 common inhalants were done with the enzymatic allergo-sorbent test (EAS) of Bio-Line (Brussels, Belgium).
Finally all patients were examined with the new in vitro test IAST® of Eurolab (Athens, Greece). IAST® (Inhalation Allergy Screen Test) is an immunoenzymatic method which uses as solid phase a balanced mixture of pollens with code name POL and another mixture of inhalant allergens with code PER. The manufacturer does not supply the exact composition of the allergens. The method is quantitative and the normal reference value is 0-35 AU/L.
Results: At least one positive skin test had 175 patients and 161 of them had an IAST® value > 35 AU/L. Of the 111 patients who were skin tests negative only one had an IAST® value > 35 AU/L. 14 patients had normal IAST value with one or more positive or weakly positive skin tests.
164 patients had at least one positive specific IgE and only one of them had an IAST® value ≤ 35 AU/L. 126 samples were negative with both IAST® and Bio-Line methods.
The geometric means of IAST® positive and negative samples were 876,3 and 12,6 AU/L respectively. Higher IAST® values observed in patients with high specific IgE to individual allergens rather than in multiple sensitivity.
In positive blood samples relative disagreement between IAST® and Bio-Line EAS was found in 6 cases (e.g. positive in both indicators with positive specific IgE only for pollen).
The statistical analysis of results of the present study shows that IAST® has (depending on the reference method) sensitivity 92-99,4%, specificity 99-100%, positive predictive value 99,4- 100% and negative predictive value 88,7-99,2%.
Conclusions: IAST® was shown to be highly sensitive and specific in differentiating asthmatics who are sensitised to common inhalants from those who are not. It is a simple, reliable method in first intention for the physician who faces a putative respiratory allergy. It is quantitative and distinguishes pollen allergy from this due to other inhalants. Moreover it is an excellent biological confirmation for a patient with questionable negative skin tests.
Το περιεχόμενο του IDEA MEDICAL NEWSLETTER είναι επιστημονικό και απευθύνεται σε γιατρούς και λοιπούς επαγγελματίες υγείας. Σε καμιά περίπτωση δεν πρέπει να χρησιμοποιηθεί από πρόσωπα που δεν έχουν τα προσόντα νόμιμης άσκησης του ιατρικού επαγγέλματος για οποιαδήποτε θεραπευτική ή διαγνωστική εφαρμογή.