Defining dried blood spot diameter: implications for measurement and specimen rejection rates

Nick Flynn; Stuart J. Moat

doi:10.1515/cclm-2025-0183

Article

Defining dried blood spot diameter: implications for measurement and specimen rejection rates

Nick Flynn and Stuart J. Moat

Published/Copyright: April 14, 2025

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From the journal Clinical Chemistry and Laboratory Medicine (CCLM) Volume 63 Issue 9

Abstract

Objectives

Dried blood spot (DBS) specimen acceptance guidelines recommend rejecting specimens based on DBS size, often expressed as a diameter. Computer vision methods can estimate DBS size from images obtained from standalone equipment, smartphone cameras or existing laboratory instrumentation. However, no consensus definition of DBS diameter exists. We assessed how different DBS diameter definitions affect measurement and specimen rejection rates.

Methods

We compared computer vision estimates of DBS diameter on 1,991 DBS using two different calculation methods and on 22 DBS where paired images were taken from either side of the filter paper. We modelled the impact on specimen rejection rate in >163,000 DBS specimens.

Results

Two different calculation methods for DBS diameter showed a mean difference <0.1 mm for circular DBS. Greater variability was observed for incorrectly applied DBS with a mean (standard deviation) difference of 0.29 (0.41) mm. DBS diameter measured from the front of the filter paper was approximately 0.41 (0.25) mm larger than from the back of the filter paper. Changing the DBS diameter definition could more than double the number of insufficient DBS (<8 mm), potentially leading to 4,000 additional repeat collections annually in the UK newborn screening programme.

Conclusions

DBS diameter definition can have a small but important and easily avoidable impact on measurement, impacting specimen rejection rates. We recommend that DBS diameter is defined as the diameter of a circle with equal area to the DBS, when measured from the opposite side of the filter paper to blood application.

Keywords: dried blood spot; computer vision; measurand; acceptability; pre-analytical; newborn screening

Corresponding author: Nick Flynn, Biochemical Genetics Unit, Cambridge University Hospitals NHS Foundation Trust, Addenbrooke’s Hospital, Cambridge Biomedical Campus, Hills Road, Cambridge, CB2 0QQ, UK, E-mail: nick.flynn@nhs.net

Funding source: NIHR Cambridge Biomedical Research Centre

Award Identifier / Grant number: BRC 1215 20014

Research ethics: The study was reviewed and approved by Cambridge University Hospitals NHS Foundation Trust Research and Development department (reference A095880).
Informed consent: Not applicable.
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Use of Large Language Models, AI and Machine Learning Tools: None declared.
Conflict of interest: The authors state no conflict of interest.
Research funding: This research was supported by the NIHR Cambridge Biomedical Centre (BRC 1215 20014).
Data availability: The data that support the findings of this study are available from the corresponding author, NF, upon reasonable request.

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Supplementary Material

This article contains supplementary material (https://doi.org/10.1515/cclm-2025-0183).

Received: 2025-02-15

Accepted: 2025-04-03

Published Online: 2025-04-14

Published in Print: 2025-08-26

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Supplementary Material

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Keywords for this article

dried blood spot; computer vision; measurand; acceptability; pre-analytical; newborn screening