capillary blood collection: advantages and disadvantages

Capillary blood collection has been around for decades. When it began, the technique was used to obtain blood from infants for genetic screening. Drawing a volume of five or ten µl from a newborn baby can be difficult and potentially harmful, so small-volume sampling had obvious applications in this area.

Capillary blood is obtained by pricking a finger in adults and a heel in infants and small children. The specimen is then collected with a pipette, placed on a glass slide or a piece of filter paper, or is absorbed by the tip of a microsampling device. Capillary blood is used for glucose measurements by transferring the blood to a test strip.

Differences in Results

The differences between capillary blood versus plasma in most cases are minimal. However, there are some discrepancies in hemoglobin and hematocrit values and in platelet counts. Glucose levels also have a small disparity. Venous blood glucose is generally slightly higher than capillary blood glucose measured at the same time. These laboratory reports need to be evaluated in light of the sampling method used.

Advantages of Capillary Blood Collection

• Only a very small amount of blood is needed, which reduces the potential for problems associated with blood loss in delicate patients. ICU patients can lose up to 2% of their total blood volume every day when venous blood sampling is done.
• Collection is simple and relatively painless. Finding a vein in an elderly person or a child can be traumatic for both them and the lab tech.
• People can be taught to do capillary blood collections at home. Diabetics routinely check their blood sugars this way using a finger-prick method with a lancet.
• Collection sites can be changed so that the risk of scarring and pain is lessened.
• Increasing adoption and implementation in labs and clinical research labs.

Disadvantages of Capillary Blood Collection

• Not all lab tests can be run on capillary samples.
• Capillary blood collection can sometimes rupture the blood cells, producing results that are inaccurate.
• Problems with bleeding and infection can occur with any/either method of collection.
• Patients may feel faint after any type of blood drawing.
• Overuse of the same area for collection can cause scarring.
• Calcified nodules can develop at the site of collection, especially in infants. The nodules usually resolve by themselves.

In general, capillary blood collection is much preferred by both end-users and lab technicians. The method is simpler, less painful, and rarely requires a "second stick." Results are comparable between capillary blood versus plasma except in a few cases. In those cases, the results need to be correlated with data from the same collection method.