During the early 1960’s, Dr Robbert Guthrie, a physician based at Buffalo Children’s Hospital, pioneered dry blood spot (DBS) testing for certain inborn errors of metabolism.
Motivated by seeing the devastating effects of the disease on his niece, Dr Gutherie realised that if caught early and intervention with a diet deplete of phenylaniline (PKU), then the disease could be managed.
This kickstarted the birth of neonatal screening, where today many inborn errors of metabolism are detected, monitored and managed before disease progression. To explore PKU in greater detail and learn about the latest therapeutic developments, visit this blog.
Around the same at the same time that Dr. Guthrie was achieving significant progress in early PKU detection using DBS, scientist at the clinical diagnostics company Ames were making big strides in capillary blood glucose monitoring. In 1965, the company launched Dextrotix where a large drop of blood was applied to a test strip left for 60 seconds to allow a glucose oxidase reaction to then washed off to reveal a colour change if glucose was detected.
This was the first time capillary blood was employed for diabetes control and monitoring. Furthermore, around the middle of the 20th century (possibly earlier), capillary blood was also being used for measuring haemoglobin using a gravimetric method employing a copper sulphate solution for analysis.
Since these early examples, the applications employing blood microsampling have become increasingly diverse and widespread. These include, measuring drug levels for, therapeutic drug monitoring, drugs of abuse testing and PK studies.
Furthermore, biomarkers, antibodies and environmental exposure makers are being increasingly measured using microsampling. Moreover, capillary blood collection has also been increasingly utilised for omics research.
In addition, the recent development of volumetric collection devices such as the Mitra device, offer a much easier way to collect capillary blood, as well allowing for processing more accurate and streamlined analysis in laboratories.
There are huge benefits to capillary blood microsampling compared to standard blood collection. It is more convenient, as samples can be collected practically anywhere (including sampling by astronauts in space!) and less painful.
Furthermore, dried microsamples are often more stable compared to liquid samples - often allowing for inexpensive shipping in ambient conditions.
However, there are drawbacks too, these include, haematocrit effects especially when working with dried blood samples, although devices like Mitra solve some of these issues.
Furthermore, there have been concerns around how the sample is collected especially when a healthcare professional is not present to assist or supervise.
Thankfully efforts are made to ensure that instructions are clear and so sample collection integrity less of a concern evidenced by the weight of successful studies published in the literature.
It is generally considered by institutions, such as the world health organisation (WHO), that the first drop of blood should be wiped away when sampling. There are a number of reasons for this.
There are two main reasons why wiping the first drop is not possible.
These are a plethora of published guidelines which all recommend wiping away at least the first drop of blood below are three examples of such recommendations.
In a document entitled “WHO Guidelines on Drawing Blood: Best Practices in Phlebotomy” published in 2010 by the World Health Organisation state the following. “Wipe away the first drop of blood because it may be contaminated with tissue fluid or debris (sloughing skin)”.
Instructions published by the Centres of Disease Control and Prevention (CDC) state “Apply slight pressure to start blood flow. Blot the first drop of blood on a gauze pad without touching the finger and discard the gauze in appropriate container.”
Health guidelines from Western Australia recommend wiping the first drop as it may be diluted by interstitial fluid, and specifically advise wiping away the first 2-3 drops for haemoglobin testing.
The fast pace of analytical and informatics development means we are increasingly able to analyse a lot more with a lot less blood. This allows us to access more remote populations and allows vulnerable people to send samples from home.
However, we need to be aware that conducting remote sampling has its own risks, and analytical result can be only as good as integrity of the collected sample.
Collecting a good quality blood sample, is crucial and so following recommendations by authorities such as the WHO and CDC, should be adhered to when developing instructions for capillary blood collection.