capillary blood collection: advantages and disadvantages

Capillary blood collection utilizing methods such as finger-sticks, heel-sticks, or other small punctures offers an alternative to traditional venous blood draws.

Once primarily used for newborn screenings, its applications have expanded significantly and are now utilized in various research and clinical settings. Below, we explore how capillary sampling works, its advantages and disadvantages, and important factors to consider for ensuring accuracy and usability.

How Capillary Blood Collection Works

Capillary blood is collected by making a small puncture in the fingertip for adults or the heel for infants and young children using a lancet. After the puncture, blood droplets are collected directly onto filter paper, in small glass capillary tubes, or using absorbent tips from microsampling devices.

These samples can then be transferred for testing or analyzed using dried blood spot methods, microsampling devices, or glucose strips, depending on the type of test being conducted.

Key Advantages of Capillary Blood Collection

• Minimal Blood Requirement: This reduces complications linked with significant blood loss, especially in vulnerable patients. For instance, ICU patients undergoing venous blood sampling can lose up to 2% of their total blood volume daily.
  
  
• Ease of Collection: The finger-stick capillary blood collection procedure is less intrusive than traditional venous blood draws and is nearly painless. With traditional blood draws, locating a vein in the arm, especially in children or the elderly, can be a challenging and distressing task.
  
  
• Home Collection: With adequate training, individuals can use a finger-stick method to perform capillary blood collections at home. This method is popular among diabetics for routine blood sugar checks, and is becoming more widely accepted by various research and healthcare industries.
  
  
• Varied Collection Sites: Using different fingertips or even other sampling sites, such as the heel of the hand or the upper arm, can minimize the risk of scarring and discomfort.
  
  
• Growing in Popularity: More labs and research facilities are recognizing and implementing capillary blood collection methods using microsampling devices.

Disadvantages of Capillary Blood Collection

• Limitations for Certain Tests: Not all laboratory tests are suitable for capillary samples; some assays, particularly those sensitive to collection volume or processing, may yield less reliable results.
  
  
• Risk of Cell Rupture (Hemolysis): Mishandling of samples can lead to cell rupture, which may distort test results.
  
  
• Potential Complications: Some patients may experience complications such as bleeding, infection, or light-headedness.
  
  
• Scarring from Repeated Lancing: Repeated use of the same site for blood collection can result in scarring.
  
  
• Complications in Infants: Small blood collection sites in infants can occasionally lead to mild complications like calcified nodules, though these typically resolve on their own.

Accuracy and Interpretation: Capillary vs. Plasma Samples

In general, the differences between capillary blood and plasma are minimal for many tests. However, readings for hemoglobin, hematocrit, and platelet counts may vary between the two sample types. For example, capillary and venous glucose measurements can show slight discrepancies when taken simultaneously. Consequently, researchers and clinicians must consider what kind of capillary blood collection procedure when interpreting results.