Measurement of IgE antibodies using liquid allergens--an inter-method and inter-laboratory quality assessment

The determination of IgE antibodies is important for the in vitro diagnosis of allergic diseases. However, not all systems currently available in the market fulfill essential quality criteria, e.g. regarding characteristics such as sensitivity and specificity, and the data do not always reflect true clinical relevance in the required fashion. Recent innovations may reduce the workload for the technician, and thus help save time and money. More importantly, they might reduce potential sources of error.

Two allergy systems, the well established Pharmacia CAP system that uses the allergens conventionally in a solid phase and the ALLERgen system that employs liquid allergens, were compared with regard to quality criteria and practicability.

Defined serum pools were checked for within-run and between-days imprecision of IgE antibody detection in two independent laboratories. Serum specimens from allergic patients and controls were tested in parallel using both methods for total and antigen-specific IgE antibody detection under standardized conditions. In addition, one laboratory working exclusively with the ALLERgen system participated in the Austrian inter-laboratory quality assessment program.

The two systems were comparable in terms of sensitivity and specificity, and also showed good correlation. Within-run evaluations were excellent for total IgE and antigen-specific IgE, and the between-days imprecision was satisfactory. Coefficients of variation were within an acceptable range for the different groups of allergens. In the external quality control program the data obtained with the ALLERgen system showed good concordance with other systems in use; up to 94% of the results were identical when considering clinically relevant sensitizations. Regarding practicability, both systems were most satisfactory for the operator. The ALLERgen system offered a certain advantage in terms of automated operation, which resulted in shorter fixed and variable phases of personnel time.

Both the Pharmacia CAP system and the ALLERgen system belong to an advanced generation of allergy test systems and are easy to handle. The reproducibility of results is good with both methods, and the imprecision data fall within an acceptable range. Thus, the ALLERgen system is a reliable in vitro system for evaluating specific and total IgE in serum, providing data equivalent to those obtained with the CAP system.