Background: British Society for Haematology guidelines for laboratories state that ideally a fresh calibration curve should be carried out with each assay batch, and always when changing reagent lots.

This laboratory used stored calibration curves until 2016, calibrating when changing reagent lots or when indicated by poor internal quality control or external quality assurance. Since 2016, a fresh calibration has been performed with every assay batch.

Aims: We evaluated the imprecision of the control results for all one-stage clotting factor assays (OSCA) performed on one Sysmex CS-2100 analyser for four years using stored curves and four years using fresh curves.

Methods: Normal and pathological internal quality controls were assayed with each batch of assays, with between 100 and 200 batches for each PT-based OSCA and 200-400 batches for each APTT-based OSCA performed against both stored and fresh curves.

Results: For PT-based OSCA, the mean CV for stored curves was 8.21% for normal controls and 8.8% for pathological controls; for fresh curves the CVs were 4.87% and 5.00% respectively. For APTT-based OSCA the values were 7.23% and 8.75% for stored curves and 5.49% and 5.45% for fresh curves. These differences are statistically significant (see Table 1).

Conclusion(s): Although internal quality control and external quality assurance performance is acceptable whether using stored or fresh curves, precision is improved using fresh curves with each batch.

Table 1

Median CV, range of CVs, number of batches of quality control material and total number of runs for each control and assay using stored and fresh calibration curves for one-stage clotting factor assays

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