ความจำเพาะและความไวของการทดสอบทางผิวหนังในการวินิจจัยโรคภูมิแพ้จมูกอักเสบต่อแมลงสาบ / พรเพ็ญ ธรรมพานิชวงค์ = The specificity and the sensitivity of skin prick test in the diagnosis of nasal allergy to cockroach / Pornpen Thampanitchawong
The allergen skin prick test is commonly used to diagnose cockroach allergic rhinitis (AR) although positive results do not always indicate that rhinitis is of allergic origin. This diagnostic study was designed to assess the specificity and the sensitivity of skin prick test in the diagnosis of nasal allergy to cockroach compared to nasal provocative test (NPT), and to determine the association between skin prick reaction and nasal provocation responses to Periplaneta americana allergen extract (CRa). Sixty three rhinitis patients were screened and 40 cases were enrolled. Twenty-two non-rhinitis with negative SPT healthy volunteers were included as control. All underwent nasal provocation tests using standardized cockroach extract. Serial ten folds dilutions of allergen extract were delivered by a metered dose pump. Nasal stuffiness, rhinorrhea, itching, and sneezing were recorded, and the amount of secretion was measured. The results showed that 22 of 40 rhinitis patients (55%) had SPT positive to cockroach antigen, 18 of them had positive reaction at least 3+. All of cockroach sensitized patents also showed positive SPT against other antigens. In NPT results, median threshold of CRa in healthy volunteers was 12.5 mg, in non-cockroach AR was 6.88 mg, and cockroach AR was 1.25 mg. The value is significantly lower in the allergic rhinitis group compared to that of the normal controls (p<0.001). There is no significant difference in median CRa threshold between cockroach and non-cockroach AR groups. Diameters of wheal of CRa skin test positivity were reversely correlated to the threshold of CRa in NPT (Rho = -0.514, p<0.001). Based on positive NPT as a gold standard (either using at least 1 out of 3 criteria or the cut-off threshold at 0.0125 mg of CRa), the specificity, sensitivity, positive predictive value (PPV), and negative predictive value (NPV) of cockroach SPT positive of at least 3+ was 71, 57, 55 and 71 percent, respectively. In conclusion, a significant reverse correlation between diameter of CRa positive wheal and the CRa nasal reactive threshold was found. SPT positive against CRa of at least 3+ has high specificity but relatively low sensitivity for the diagnosis of cockroach nasal allergy.