The Test Sample
What is being tested?
Bilirubin is an orange-yellow pigment found in bile. The normal life-span of red blood cells in the circulation is 120 days. When they are broken down the pigment giving them their characteristic red colour, haemoglobin, (whose role is to carry oxygen to the tissues) is converted to unconjugated bilirubin. Only small amounts of bilirubin are normally present in the blood. Unconjugated bilirubin is not water soluble so it binds to a protein in the blood which then carries it to the liver. Within the liver, each unconjugated bilirubin molecule has a sugar molecule attached to it to form water soluble conjugated bilirubin. This is secreted into bile and carried to the intestine where bacteria break it down, eventually producing the brown pigment that colours normal stools.
How is the sample collected for testing?
In adults, blood is collected by needle from a vein in the arm. In newborns, a few drops of blood are usually collected from a heel-prick. Sometimes in newborns bilirubin is estimated by placing an instrument on the skin (a transcutaneous bilirubin meter).
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is necessary. The blood sample should ideally be protected from bright light before analysis.