title: The use of dried blood spot sampling for the measurement of HbA1c: a cross-sectional study.
abstract: BACKGROUND
  The use of dried blood spot (DBS) sampling is an alternative to traditional venous blood collection, and particularly useful for people living in rural and remote areas, and for those who are infirm, house-bound or time-poor. The objective of this study was to assess whether the measurement of glycated haemoglobin A1c (HbA1c) in DBS samples provided comparative and acceptably precise results.
  
  
  METHODS
  Venous and capillary blood samples were collected from 115 adult participants. After proper instruction, each participant punctured his/her own finger and collected capillary blood samples on pieces of a proprietary cellulose filter paper. Each filter paper was subsequently placed inside a breathable envelope, stored at room temperature, and processed on the same day (D0), four (D4), seven (D7) and fourteen (D14) days after collection. HbA1c was measured in duplicates/triplicates in whole venous blood (WB), capillary blood (capDBS) and venous blood placed on the matrix paper (venDBS), by turbidimetric inhibition immunoassay. Intra-assay coefficients of variation (CV) were calculated. DBS values were compared to WB results using linear regression, Bland-Altman plots and cross-validation models.
  
  
  RESULTS
  Eleven and 56 patients had type 1 and type 2 diabetes mellitus, respectively. Mean HbA1c levels were 6.22 ± 1.11 % for WB samples (n = 115). The median intra-assay CV was lower than 3 % for WB and capDBS on all days. Results from capDBS and venDBS showed high correlation and agreement to WB results, with narrow 95 % limits of agreement (except for results from D14 samples), as observed in Bland-Altman plots. When capDBS values were applied to equations derived from regression analyses, results approached those of WB values. A cross-validation model showed that capDBS results on D0, D4 and D7 were close to the WB results, with prediction intervals that were narrow enough to be clinically acceptable.
  
  
  CONCLUSIONS
  The measurement of HbA1c from DBS samples provided results that were comparable to results from WB samples, if measured up to seven days after collection. Intra-assay coefficients of variation were low, results were in agreement with the gold-standard, and prediction intervals were clinically acceptable. The measurement of HbA1c through DBS sampling may be considered in situations where traditional venipuncture is not available.
  
  
  BACKGROUND
  Australian New Zealand Clinical Trials Registry ID ACTRN12613000769785.
authors.affiliation: Department of Genome Sciences, The John Curtin School of Medical Research, The Australian National University, 131 Garran Rd, Canberra, Acton ACT 2601 Australia.
authors.forename: Claudio A
authors.initials: CA
authors.lastname: Mastronardi
authors.affiliation: Australian Phenomics Facility, The Australian National University, 117 Garran Rd, Canberra, Acton ACT 2601 Australia.
authors.forename: Belinda
authors.initials: B
authors.lastname: Whittle
authors.affiliation: Australian Phenomics Facility, The Australian National University, 117 Garran Rd, Canberra, Acton ACT 2601 Australia.
authors.forename: Robert
authors.initials: R
authors.lastname: Tunningley
authors.affiliation: Statistical Consulting Unit, The Australian National University, 27 Union Lane, Canberra, Acton ACT 2601 Australia.
authors.forename: Teresa
authors.initials: T
authors.lastname: Neeman
authors.affiliation: Department of Genome Sciences, The John Curtin School of Medical Research, The Australian National University, 131 Garran Rd, Canberra, Acton ACT 2601 Australia.
authors.forename: Gilberto
authors.initials: G
authors.lastname: Paz-Filho
keywords: Diabetes; Dried blood spot testing; HbA1c; Hemoglobin A1c; Turbidimetry