Development of a bloodspot assay for insulin

Abstract

Background: Bloodspot assays for hormones have advantages of ease of collection/transportation, minimal invasiveness and small blood volume. Such an approach would be of use in epidemiological studies of insulin resistance in children and neonates.

Methods: A two-site chemiluminescent immunoassay for the quantitation of insulin in bloodspots dried on filter paper, based on modifications of a commercially available kit, was used. Analysis was carried out on two 3-mm diameter discs punched out from whole blood standards and test samples.

Results: The detection limit of the assay was 5.9 pmol/l of whole blood, with mean intra-assay CV and mean inter-assay CV being <15% above 24 pmol/l. The mean recovery of added insulin was 83%. Comparison of paired whole bloodspots and serum samples collected simultaneously gave a correlation of 0.89. The bloodspot insulin concentrations were stable in excess of 2 months when stored at -20 degrees C and were not susceptible to degradation after four freeze-thaw cycles.

Conclusions: This simple and convenient method is suitable for the measurement of insulin in small volumes of blood collected on filter paper cards and can be applied to epidemiological studies of insulin resistance.