does capillary blood yield the same venous blood quality results?

Blood vessels cover quite a bit of real estate in the body. Laid end-to-end the adult vascular system could reach 100,000 miles in length, according to The Franklin Institute. Each type of blood vessel serves an essential function.

The three types of vessels play distinct roles in the circulation process—but what about in blood testing? Are all vessels equally valuable when blood samples are needed for testing?

Arterial Blood Vs. Venous Blood & How Capillary Blood Is Different From Both?

• Arterial blood (oxygenated blood) is pumped and circulated in the pulmonary vein, the left chambers of the heart, and in the arteries through out the body.
• Venous blood (deoxygenated blood) is circulated and pumped through the peripheral blood vessels. The blood then travels through the venous system into the right atrium of the heart. Deoxygenated blood is pushed through the heart by the right ventricle to the lungs using the pulmonary artery which is divided in two branches. The blood then passes through the lungs and gets oxygenated. Coming through the pulmonary veins it returns to the left atrium.
• Capillary blood is not identical to venous blood or arterial blood. However, in many applications, these types of blood samples yield quality results for researchers and physicians alike.

Capillary blood is a combination of arterial and venous blood. From the right side of the heart through the lungs, oxygenated arterial blood flows into the capillaries. There, oxygen and nutrients are distributed and exchanged for carbon dioxide. The waste-containing deoxygenated blood then travels through the veins back to the heart.

Being at the center of this process, the capillary turns out to be a useful site for blood sampling.

Where Capillary Blood Sampling Offers Greatest Value

While lab reference values are often set up for traditional venipuncture, there are many situations when capillary blood is preferred over a venous specimen.

Capillary blood draws for dry blood spot (DBS) testing are easier on the patient or subject, and the smaller volume collected is simpler to handle, especially in remote or at home settings.

When required, patients are typically comfortable collecting their own samples for monitoring purposes. Blood draws via capillary microsampling are more comfortable for pediatric patients and the elderly, and are preferred for burn patients.

Point-of-care Testing

In particular, is more convenient with microsampling. In some settings, fast, on-site blood testing would be impossible or unwieldy without the use of blood microsampling. Capillary blood proved critical in diagnosing Ebola quickly in the field and helping to control the recent outbreak.

In Research Applications

Another set of capillary blood sampling advantages exists. When capillary sampling is used, fewer animals are needed, with a larger number of samples possible from each. This saves resources and can improve the accuracy of results, as the same individual can be sampled consistently, reducing data adjustment needs.

Correlation Between Venipuncture and Finger-Prick Blood Results

There is a great debate on whether a correlation exists between venous and finger-prick blood results. Though there is not a definitive conclusion to this debate, there is much research to show that capillary blood can yield quality results, which may correlate to or even match traditional venipuncture reference values. Check out these 5 articles to learn more.

1. Osteresch B, Cramer B, Humpf H.U. (2016) Analysis of Ochratoxin A in Dried Blood Spots - Correlation between Venous and Finger-Prick Blood; the Influence of Hematocrit and Spotted Volume. Journal of chromatography. February
2. Keevil B.G., Fildes J, Baynes A, Yonan N. (2009) Liquid chromatography-mass spectrometry measurement of tacrolimus in finger-prick samples compared with venous whole blood samples. Annals of Clinical Biochemistry. 46(Pt 2):144-5
3. Spooner N, Ramakrishnan Y, Barfield M, Miller S.R. (2010) Use of DBS sample collection to determine circulating drug concentrations in clinical trials: Practicalities and considerations. Bioanalysis. 2(8):1515-22
4. Jensen M.E, Ducharme F, Theoret Y, Delvin E.E. (2016) Assessing vitamin D nutritional status: Is capillary blood adequate? Clinica Chimica Acta. international journal of clinical chemistry 457
5. Lachance S., Theberge M.C., Havard, G., Levesque A. (2016) Comparison of blood microsampling with DBS and conventional blood collection techniques used in a midazolam biostudy. Bioanalysis. 8(8)

Weigh in on the great debate of venous vs finger-prick blood in the comments section below.