Analytes
Total cholesterol, triglycerides and CRP from serum and DBS and glycated haemoglobin from whole blood or serum and DBS were measured using a Siemens Dimension Xpand clinical chemistry analyser (Siemens Healthcare Ltd, Camberley, Surrey, UK). Method details including extraction from DBS, as well as reagents, control quality materials and QC information can be found in Supplementary Materials Except for CRP, the use of third-party reagents (Randox Laboratories, County Antrim, UK) allowed assays to be programmed manually on the analyser and enabled the parameters recommended for serum assays to be adapted for the higher sensitivity required for DBS analysis. This approach kept the serum and DBS assays as closely aligned as possible to reduce bias between methods. CRP was assayed using the Siemens Dimension Xpand CardioPhase® high sensitivity assay. Serum CRP was measured according to the manufacturer’s instructions. To use the same CRP method for DBS, the assay was calibrated using a 50-fold dilution in PBS of the manufacturer’s recommended kit calibrator (CCRP calibrator). This dilution was chosen to be equivalent to the CRP in the DBS eluent. In all other aspects the assay was run using the manufacturer’s protocol for serum CRP and provided equivalent results for the sample types (Supplementary Materials Measurements of triglycerides, HbA1c and CRP did not meet the assumption of normality assessed using Shapiro–Wilk tests. To overcome this, triglyceride and CRP data were log transformed and inverse measures for HbA1c were used for equivalency. (Supplementary Materials 