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capillary blood collection: advantages and disadvantages

a nurse collects a small sample of capillary blood from an infants heel

Capillary blood collection, a method that's been in practice for decades, primarily started as a technique to draw blood from infants for genetic screenings. Since a significant blood volume extraction from newborns is problematic, capillary collection using a heel stick to collect a few micro-sized drops of blood offered a less invasive approach. Today, the microsampling method is used for a wide range of purposes. But like all techniques, it has its pros and cons.

Capillary Blood Collection: How It Works

Capillary blood is typically collected by using a lancet to prick the fingertip in adults, or the heel in infants and small children. The blood drop that forms on the fingertip or the heel can then be collected via a tiny glass capillary tube and transferred to a glass slide, or applied to filter paper, or absorbed via the tip of a microsampling device.

The finger-stick capillary blood collection technique is commonly used for taking glucose measurements, where the blood sample is directly transferred to a test strip, which can be inserted into a digital device to get a blood glucose level reading.

Comparing Capillary Blood and Plasma

Generally, the variance in results between capillary blood and plasma is minimal. However, certain readings like hemoglobin, hematocrit values, and platelet counts can show differences.

Venous blood glucose levels are often marginally higher than capillary glucose levels when measured concurrently. Hence, when interpreting results, the sampling method used must be taken into account.

Advantages of Capillary Blood Collection

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Growing in Popularity: More labs and research facilities are recognizing and implementing capillary blood collection methods using microsampling devices.

Disadvantages of Capillary Blood Collection

  1. Test Limitations: Not all laboratory tests are suitable for capillary samples.

  2. Risk of Rupturing Cells: This can lead to inaccurate results.

  3. Potential Complications: Both bleeding and infection risks are present with any blood sample collection event, irrespective of the method.

  4. Light-headedness: Some patients may feel faint post-procedure.

  5. Scarring: Repeated lancing of the same collection area can lead to scarring.

  6. Calcified Nodules: Especially in infants, these can develop at the collection site with repeated sampling. Fortunately, they typically dissipate on their own.

By and large, capillary blood collection is favored by both patients and lab technicians due to its simplicity, minimal discomfort, and efficiency. While results are largely congruent between capillary blood and plasma, it's vital to correlate the readings with the respective collection method.

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