Laboratory identification of factor VIII inhibitors in the real world: the experience from Australasia

Abstract

The laboratory has a key role in the initial detection of factor inhibitors and an ongoing role in the measurement of inhibitor titres during the course of inhibitor eradication therapy. The most commonly seen factor inhibitors are those directed against factor VIII (FVIII), usually detected either using the original or Nijmegen-modified Bethesda assay. In view of previously demonstrated high variability in laboratory results for inhibitor assays, we have more extensively examined laboratory performance in the identification of FVIII inhibitors. Over the past 3 years, we conducted two questionnaire-based surveys and two wet-challenge surveys utilizing eight samples comprising no FVIII inhibitor (n = 1), or low-titre (n = 2), medium-titre (n = 3) or high-titre (n = 2) FVIII inhibitor. Four samples were tested by 42 laboratories in 2007, and four by 52 laboratories in 2009. High inter-laboratory variation was evident, with CVs around 50% not uncommon, and some 10% of all laboratories (or around 15% of laboratories using Bethesda method) failed to detect low-level inhibitors of around 1 BU mL(-1). Laboratories using the Nijmegen method appeared to perform better than those using a standard Bethesda assay, with lower evident assay variation and no false negatives. There was a wide variety of laboratory practice, with no two laboratories using exactly the same process for testing and interpretation of factor inhibitor findings. In conclusion, our study indicates that there is still much need for standardization and improvement in factor inhibitor detection, and we hope that our findings provide a basis for future improvements in this area.

Laboratory testing for factor inhibitors

“…Nevertheless, inter‐laboratory coefficients of variation (CV) approaching (and sometimes exceeding) 50% are evidenced by various EQA groups, inclusive of ECAT (External quality Control of Assays and Tests) Foundation, NEQAS (UK National External Quality Assurance Scheme) and RCPA (Royal College of Pathologists of Australasia) (Fig. ) . This variability has not improved over the years.…”

“…This variability has not improved over the years. Reasons for such high variability largely derive from assay variability, which can occur at any stage within the assay, including choice and source of laboratory reagents, buffering (yes, no, how), NPP, etc., such that no two laboratories participating in the RCPA EQA programme could be found to be using exactly the same procedure in one analysis . Although NA tend to provide lower variability than BA , how laboratories perform NA varies almost as much as how laboratories perform BA; thus, variability still remains high.…”

Variability between laboratories performing coagulation tests with identical platforms: a nationwide evaluation study

“…Another investigation used the results of the Italian External Quality Assessment Scheme and found a wide variability in estimation of quantitative D-Dimers (coefficient of variation up to 47%) [18]. A high degree of variation between laboratories in the identification of coagulation factor inhibitors was shown in several investigations, which used data of external quality assessment programs [7,19-21]. Other investigations identified the type of the reagent [22], the method of the assay [23] and the calibrator [24,25] as factors that bias the measurements between different laboratories and the coagulometer influencing the precision of the measurements [22].…”

The role of the laboratory in diagnosis and management of inhibitory antibodies in haemophilia

“…[12][13][14] For clinicians, it is of importance to have direct dialogue with the laboratory on how these assays are performed. [12][13][14] For clinicians, it is of importance to have direct dialogue with the laboratory on how these assays are performed.…”