comparing capillary blood with venous blood: understanding the difference and their uses

The intricate network of blood vessels in the human body stretches an astonishing 60,000 miles if laid end-to-end. Each vessel type plays a pivotal role in our circulatory system. 

Three Blood Vessel Types: A Quick Rundown

1. Arterial Blood: Oxygen-rich, this blood circulates through the pulmonary vein, the heart's left chambers, and the arteries across the body.
2. Venous Blood: Deoxygenated blood flows through peripheral vessels, then via the venous system to the heart's right atrium. From the right ventricle, it's transported to the lungs through the pulmonary artery. After oxygenation in the lungs, it returns to the heart's left atrium through pulmonary veins.
3. Capillary Blood: A unique mix of arterial and venous blood, capillaries bridge the gap between these two types. As arterial blood flows into capillaries, it offloads oxygen and nutrients, picks up waste, and then turns into deoxygenated blood, which travels back to the heart via veins. With its central role in the exchange process, capillaries are often chosen as the preferred blood sampling site.

With its central role in the exchange process, capillaries are often chosen as the preferred blood sampling site. How does this translate when it comes to analysis of blood samples?

The Value of Capillary Blood Sampling

While lab benchmarks commonly use venous samples, capillary blood offers several advantages:

• Patient Comfort: Dry blood spot (DBS) testing using capillary blood is less invasive, making it preferable for remote or home settings.
  
  
• Self-Collection: Patients can easily collect their samples, which is especially beneficial for monitoring chronic conditions.
  
  
• Special Populations: It's the preferred method for pediatrics, elderly, and burn patients.
  
  
• Point-of-Care Testing: Capillary blood enables quick, on-site blood tests. Its crucial role was evident in the rapid diagnosis and management of the Ebola outbreak.
  
  
• Research: Fewer animals are required when using capillary samples, research more resource-efficient and accurate by ensuring consistent sampling from the same subject.

The Ongoing Debate: Venous Vs. Finger-Prick Blood

A significant discussion revolves around whether capillary (finger-prick) results mirror venous results. While a conclusive answer remains elusive, extensive research indicates that capillary blood can produce high-quality results, closely aligning with or matching venous reference values. 

Sources:

• 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
  
  
• 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
  
  
• 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
  
  
• 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
  
  
• 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)