Capillary Blood Collection Course Description A capillary sample is a blood specimen collected by pricking the skin and accessing the capillaries, tiny blood vessels near the surface of the skin. Capillary sampling from a finger, heel or (rarely) an ear lobe may be performed on patients of any age, for specific tests that require small quantities of blood. Acquiring a good quality capillary blood sample is essential to ensuring results are precise and accurate when conducting point of care tests. This training module will educate you about the correct way to collect blood, the common pitfalls to avoid and ensure that you get the most from your point of care testing equipment. Work your way through the lessons and complete the quiz at the end. When you achieve a score above 80 % you’ll earn a certificate of competency. Please note you must be registered on the site in order to enrol on this course.
What is Capillary Blood? Collecting capillary blood involves accessing the capillary beds which run through the subcutaneous layer of the skin by puncturing the dermis layer. Blood obtained via skin puncture is a mixture of undetermined proportions of blood from arterioles, venules, capillaries, plus interstitial and intracellular fluids. The proportion of arterial blood is greater than that of venous blood, due to the increased pressure in the arterioles leading into the capillaries versus the pressure in the venules exiting the capillaries.
How blood travels through blood vessels Heart➞ Artery ➞ Arteriole ➞ Capillary ➞ Venule ➞ Vein ➞ Heart Because of the way blood travels it is important that consistent technique based on best practice is employed, to ensure the quality of examination results which typically require small quantities of blood (e.g. point of care testing).
Limitations There are instances when capillary blood collection may be inappropriate, for example: Patients who are severely dehydrated. Individuals with poor circulation Tests that require large volumes of blood (e.g. > 500 µL) It is important to understand that there are differences between some analytes in capillary blood as compared to venous or arterial blood specimens. For example glucose, potassium, total protein, and calcium have been reported to show statistically and/or clinically important differences. With the exception of glucose, the concentration of these analytes is lower in capillary blood. Similarly, when undertaking an INR test where prothrombin (clotting) time is measured there is increased imprecision due to pre-analytical factors such as the length of time it takes to collect the sample and initiate a test. Limitations such as this are not a factor when a laboratory tests venous samples.
Device Selection The Clinical Laboratory Standards Institute (CLSI) recommend that a skin puncture device is a sterile, disposable, single-use device with a permanently retractable blade or needle to reduce the possibility of accidental needlestick injuries and reuse. There are two types of lancing devices that are used for collection of capillary blood: puncture devices and incision devices. Puncture devices such as the Unistik 3 Extra puncture the skin by inserting a needle vertically into the tissue and are preferable for sites that are repeatedly punctured (i.e. blood glucose monitoring). Incision devices such as the Unistik 3 Neonatal slice through the capillary beds, are less painful than puncture devices and require fewer repeat incision/shorter collection times. These are the main reason they are recommended for infant heel sticks or larger volumes that may be required by laboratories. A lancet slightly below the estimated depth required should be selected because the pressure applied when performing the fingerstick compresses the skin, causing a puncture depth slightly deeper than the lancet length. Naturally thicker lancets with higher penetration depths are more painful, however the blood volume obtained will also increase which can in many cases be more beneficial than having to perform rep