Atopy in Omani patients with asthma

Abstract

Objectives: To determine the range of serum IgE in healthy subjects and in asthmatic patients in Oman and to assess the degree of atopy in the asthmatic patients.

Method: Serum IgE and in vivo (the skin prick test) and in vitro (the ImmunoCAP test) allergen-specific IgE levels were measured in 44 patients with asthma. Control groups were 19 healthy subjects and 27 asymptomatic allergic subjects.

Results: The normal range for serum IgE in the Omani population was established at ≥ 101 IU/ml. The geometric mean (and 95% confidence interval) for asthmatic patients was 468 IU/ml (323-676). Positive results for allergen-specific IgE, defined as responses to ≥ 1 allergen mix in the ImmunoCAP and to ≥ 3 allergens in the skin prick test, occurred in 26/35 (74%) and in 34/44(77%) asthmatic patients respectively. Six out of 38 patients with serum IgE ≥ 101 IU/ml and 2/6 with levels <101 IU/ml gave negative and positive results respectively in the skin prick test. Overall, the degree of reactivity in the skin prick test correlated with the level of total serum IgE (r= 0.54, p<0.001). A similar correlation could not be established with ImmunoCAP reactivity, but sIgE levels ≥ 101 IU/ml were supported by a high frequency of positive ImmunoCAP responses for the majority of allergen mixes.

Conclusions: Total serum IgE levels should be routinely monitored in asthmatic subjects as this may give an indication of atopy where skin prick testing is not indicated. Since in a minority of patients serum IgE levels and skin prick results do not predict in the same direction, all laboratory data should be interpreted in context of clinical history.

Keywords: Oman; asthma; atopy.

Figure 1.

Ranges of sIgE levels in normal control subjects, asymptomatic allergic subjects and patients with asthma. Bars represent geometric mean values sIgE, with 95% confidence limits

Figure 2.

Correlation between sIgE levels and degree of positivity in the skin prick test. The horizontal line represents upper limit of normal range for IgE. Vertical line represents demarcation of overall negative and positive results in SPT.