37.3.2. Freelite and Hevylite Precision on the SPAPLUS

Chapter 37

37.3.2. Freelite and Hevylite Precision on the SPAPLUS

The SPAPLUS maintains precision through a combination of acid/alkali cuvette washing and an innovative reaction cuvette mixing system. Air pressure is used in place of stirrers to mix the reaction mixture in a U-shaped cuvette. No physical contact is made with the reaction mixture, thereby removing any possibility of carry-over on a stirrer. Assessment of the performance of SPAPLUS CSF assays by Benard et al.[1148] and Laurent et al.[1149] indicated that carry over was not observed during routine use, and that serum and CSF analysis can be effectively integrated on a single SPAPLUS instrument to optimise laboratory workflow.

During Freelite assay validation, assay precision was assessed using 3 control fluids that ranged in concentration from 7.2 mg/L to 142.1 mg/L. The maximum intra- and inter-assay imprecision for κ or λ Freelite assays was 3.4% and 4.2%, respectively. An independent study by Ludwig et al.[1155] reported within run precision of 2.5-7% and 2.2-2.3% for Freelite κ and λ sFLC assays, respectively. The authors also assessed the day-to-day performance and identified precision of 3.3-3.6% and 5.3-6.1% for Freelite κ and λ, respectively. These findings have been replicated by a number of other laboratories[1147][1149][1150][1151].

A precision study of the 6 Hevylite reagents, by Mirbahai et al.[1152] reported maximum intra- and inter-assay imprecision of 3.2% and 4.7%, respectively. Jacobs et al.[1065] assessed the routine performance of Hevylite assays using routine clinical samples and a number of EQA samples. All 6 Hevylite assays demonstrated excellent precision, with CV results that varied between 2.2-7.4%. These findings were supported by Arkir et al.[1153] who described intra- and inter-assay precision of 0.7-2.9% and 1.5-8.3%, respectively.