Laboratory MedNews

Capillary Puncture
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There are different ways to draw blood from a patient and capillary puncture is one of them.  If you compare it with venipuncture and arterial puncture, it is the easiest way to obtain a blood specimen. Usually doctors request the procedure when there is minimal volume of blood needed. If you have a blood request stating capillary puncture in the laboratory request form, here are some basic information about the procedure.

Capillaries

Also known as the “finger stick”, the capillary puncture involves the smallest blood vessels in the body. Since the capillaries are found all throughout the body and in a more superficial location, it only involves poking the skin with a sharp object called a lancet.  The most common sites for specimen collection are the palmar surfaces of the fingers, ear lobe and big toe or heel for the infants. Once the blood starts to ooze from the punctured site, the medical worker will collect the specimen in a capillary tube or in an appropriate specimen container.

Preparation

There are no special patient preparations indicated for capillary puncture. In fact, it only requires minimal training to correctly perform the blood collection. Even non- health workers can obtain the blood provided that they have the necessary equipment and basic knowledge on the proper collection technique. Oftentimes, diabetic patients are the most common lay persons who perform the capillary puncture at home for their daily blood sugar monitoring.

Procedure

The principle in obtaining blood through capillary puncture is the same with venipuncture and arterial puncture. Of course, the health worker needs to correctly identify the patient and choose the most appropriate site. Highly calloused fingers or those with skin injuries like hematoma and bruises and edematous areas are not recommended. Once the health provider has settled with the site, he/she has to clean the site of puncture with a cotton and alcohol starting from the center moving outwards. Using a swift and deliberate motion, he/she will then puncture the skin with a lancet, wipe the first drop of blood and collect the blood using a capillary tube.

Precautions

During the collection, squeezing of the punctured must be avoided. It leads to dilution of blood with tissue juices, thereby leading to erroneous results. Since young children are the common patients indicated for capillary puncture, assistance from adults and use of restraining devices may be necessary. If your kids are the patients, you must help the health worker explain the procedure to your child. Be truthful about what to expect. Tell them about the minimal but tolerable pain that they will feel. Do not tell them it does not hurt, because it does. Reassure them though that the pain is tolerable.

Aftercare

Since capillary puncture involves a minor puncture, there are no known health risks for it, if performed by knowledgeable personnel. However, you must apply pressure to the site for 3 to 5 minutes to stop the bleeding. The whole procedure only takes up to 5 minutes to complete. After the capillary puncture, you can always go back to your regular activities.

In the laboratory, it is crucial that the clinical laboratory scientist performs the tests reliably, because the doctor bases his diagnosis on these laboratory results. Any source of error therefore is eliminated to ensure that all results are accurate. One source of unreliable results is hemolysis.   Hemolysis is the destruction or rupture of red blood cells (RBCs) causing the release of hemoglobin.   An indication of hemolysis is a pink colored serum or plasma.

Here are pointers to avoid hemolysis in blood samples.

1. Do not use wet materials because water is a hypotonic solution that causes lysis of RBCs.

2. Do not squirt blood directly into the test tube. The rapid flow may cause hemolysis. Allow the blood instead to ooze at the sides of the tube.

3. Remove the needle before transferring the blood to appropriate containers, the small opening of the needle may cause hemolysis.

4. Do not centrifuge blood if it still has not clotted properly.

5. Do not rim or ring the blood several times. This is one major source of hemolysis.

6. Do not freeze whole blood right after collection.

7. Do not vigorously shake whole blood, to avoid hemolysis in blood samples.

8. Do not expose the whole blood specimen to excessively low and hot temperatures.

9. Do not prolong tourniquet application more than necessary.

10.  Transfer the serum immediately to a different container to reduce the propensity for hemolysis.

11.  Do not pull the plunger too quickly. If the bore of the needle is small, it may cause hemolysis

12.   Allow the site to dry first after sterilization.  The alcohol still present in the area may come in contact with your sample and may produce hemolysis.

13.  There should be a proper angle of the needle to the vein to avoid transfixation, which may cause hemolysis.

14.  Any application of mechanical trauma or pressure on the blood sample will cause hemolysis, whether during collection, processing, or transportation.

Avoid hemolysis in blood samples at all cost, as this would produce unreliable results.  Unreliable results would lead to misdiagnosis. Misdiagnosis by the doctor because of your inaccurate results would endanger the life of the patient.  Remember these pointers on how to avoid hemolysis in blood samples and feel confident and secure that you are giving out your best service to patients.  Consider each patient as an important individual who deserves to  receive reliable results.