Analytical goals for the determination of HbA₂

We present a study aimed to define the analytical goals for the determination of hemoglobin A₂, a minor hemoglobin present in human blood normally accounting from 2.5 % to 3.3 % of total hemoglobin, and typically increased up to 6 % – 7 % in subjects carriers of β-thalassemia.

The analytical goals have been derived using two approaches, the first one based on biologic variation, and the second one based on the opinion of experts.

The data obtained by studying 17 adult non-carrier healthy subjects, from whom we took blood samples every 2 weeks for 2.0 months, indicated a small intraindividual biologic variation (CV I of 0.7 % ), with respect to a larger between-subject variation (CV G of 7.7 % ). The minimum levels for imprecision, bias and total error derived from the analysis of these data were: 0.5 % , 2.9 % and 4.5 % , respectively. The limits derived from the opinion of experts were based on a questionnaire with three clinical cases, which was circulated among two teams of international experts, and on a discussion about the clinical needs. The average total error derived from such surveys ranged between 7.0 % and 9.5 % .

The various methods to derive analytical performance goals gave different limits, thus indicating the need for an increased communication between clinicians and laboratory professionals on this matter.