Comparison of sample types for N-terminal pro-B-type natriuretic peptide measured on the Siemens Immulite 2500 and Dimension Vista LOCI methods.

Background: Measurement of serum natriuretic peptides is recommended in patients with suspected heart failure. Assays for N-terminal pro-B-type natriuretic peptide (NT-proBNP) are available on several platforms and can be measured in serum or heparinized plasma. Siemens Healthcare Diagnostics do not recommend the use of serum for the Immulite NT-proBNP assay. Serum offers some practical advantages over plasma. We investigated the suitability of serum for use with the Immulite and Dimension Vista LOCI methods.
Methods: Paired serum and heparinized plasma samples were drawn from patients in the Cardiology Department over a 48-h period. Samples spanning the NT-proBNP concentration range 50-60,000 ng/L were analysed using the Siemens Immulite 2500 and Dimension Vista LOCI methods.
Results: There was no significant difference between serum NT-proBNP concentrations on either platform (P = 0.0665). Plasma NT-proBNP measured using the Immulite were moderately higher than on Vista (P < 0.0001). There was a small but statistically significant difference between plasma and serum NT-proBNP measured using the Immulite (P = 0.0002) with plasma values higher than serum. A similar comparison between plasma and serum NT-proBNP measured using the Vista showed no difference (P = 0.3662).
Conclusions: We have demonstrated the suitability of serum for use on the Immulite 2500. Bland-Altman comparative analysis indicated minimal bias between both serum methods near the clinical cut-off level below which heart failure is considered unlikely (400 ng/L) up to the highest concentration tested (60,000 ng/L).