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Phenylketonuria test
Phenylketonuria test
Phenylketonuria test
Phenylketonuria test
Capillary sample
Capillary sample

Capillary sample
Definition:
A collection of a specimen for laboratory testing performed on blood or blood components by pricking the skin in an area and collecting a small amount of capillary blood.

Alternative Names:
Blood sample - capillary; Fingerstick; Heelstick

How the test is performed:
Some blood tests may be performed on blood obtained by pricking the skin of the finger, heel, or other areas (capillary blood) and collecting a drop (or a few drops) of blood on a test strip or into a small container.

The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test:
The preparation varies with the test performed.
How the test will feel:
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed:

Blood is used by the body for transportation of oxygen, food, waste products, and other materials within the body. It is also used for regulation of body temperature, regulation of fluids, and acid-base equilibrium. Blood is made up of a fluid portion (plasma) and a cellular portion. Plasma contains various substances dissolved in the fluid. The cellular portion consists primarily of red blood cells, but also includes white blood cells and platelets. Because blood is used for multiple functions within the blood, tests on the blood or its components may give valuable clues in the diagnosis of a multitude of medical conditions.

Capillary blood sampling offers several advantages:

1. It is relatively easy to obtain (often it is very difficult to obtain blood by sampling the veins, especially in infants).

2. There are several collection sites on the body (heel, fingertips, etc.) and these can be rotated.

3. Testing can be performed at home and with minimal training. For example diabetics must check their blood sugar several times a day using capillary blood sampling.

There are some disadvantages to capillary blood sampling. First, there is a limited amount of blood that can be obtained using this method. Second, there are some risks associated with the procedure (see below). Third, capillary blood sampling may provide inaccurate results, such as falsely elevated sugar, electrolyte, and blood count values.
Normal Values:
See the specific test.
What abnormal results mean:
Results vary depending on the test performed.
What the risks are:
  • excessive bleeding
  • fainting or feeling light-headed
  • infection (a slight risk any time the skin is broken)
  • scarring (occurs when there have been multiple punctures in the same area)
  • calcified nodules (sometimes occurs in infants, but usually disappear by 30 months of age)
Special considerations:

Capillary blood sampling is very useful when very small amounts of blood are needed or when blood is very difficult to obtain, such as in infants. Many times, however, when a larger sample is needed, the blood must be obtained from a vein (venipuncture).
Review Date: 11/25/2001
Reviewed By: Jonathan Fanaroff, M.D., Department of Pediatrics, Rainbow Babies and Children's Hospital, Case Western Reserve University, Cleveland, OH. Review provided by VeriMed Healthcare Network.
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