Methods: NS were collected with FD and SP in 15 house dust mite (HDM) allergic rhinitis (AR) patients and 15 controls. During processing, saline solution was added in order to mobilize the NS. For each sample, the volume to be added was calculated, based on the weight of collected NS, in order to obtain a fixed dilution. In a second experiment, NS were collected in two HDM AR patients (re-recruited from first experiment) with FD and SP on 4 consecutive days. This experiment was performed once with fixed volume and once with fixed dilution. In a third experiment, NS were collected with FD, EP and SP in 13 HDM AR patients (re-recruited from first experiment). During processing, a fixed volume of saline solution was added: 1 ml for FD, 2 ml for EP and 3 ml for SP. Total IgE and hx2-IgE were measured with the UniCap system.
Results: In the experiment with fixed dilution, levels of total IgE and HDM IgE were significantly higher in HDM AR patients compared to controls. With the FD, total IgE and HDM IgE were below the detection limit (BDL) in 2 and resp. 6 out of 15 AR patients. With the SP, total IgE and HDM IgE were BDL in 3 and resp. 4 patients. When comparing FD and SP on 4 consecutive days, the reproducibility to measure IgE levels was better with SP. In the third experiment with a fixed volume, total IgE and HDM IgE were BDL in 3 and resp. 6 out of 13 AR patients when using FD and EP. With the SP, total IgE and HDM IgE levels were BDL in 5 and resp. 7 patients.
Discussion: Each method has some advantages and disadvantages. The SP method seems to be more reproducible than the FD method, which makes it more suitable for repeated measurements and monitoring. However, SP are unsuitable for serial measurements on the same day, as they cause stimulation of the nasal mucosa. In this setting, FD are preferable. EP are intermediate in size to FD and SP and could be of interest in a pediatric setting. When comparing fixed volume to fixed dilution processing, the latter is more time consuming and prone to error. However, fixed dilution has the advantage of a fixed detection limit for all samples. Therefore, this method is recommended when measuring IgE or other mediators that are present at low concentrations and thus often BDL.