Between the arteries that carry blood away from the heart and veins that carry the blood back, there are tiny blood vessels that feed the tissues with oxygen and nutrients, called capillaries. When the tip of the finger is pricked, it is capillary blood that comes out. This is capillary blood sampling.
From the time of Hippocrates in the 5th century BC, physicians have been drawing blood from their patients. Up until the end of the 19th century, bloodletting was a "heroic treatment" -- a therapy that was intended to save the patient but frequently had the opposite effect. Doctors bled their patients, often with leeches, to get rid of the "bad humors" which were believed to cause disease.
Sir William Harvey was an English doctor in the early 1600s who identified the circulatory system in the human body. Capillaries, the connection between the arteries and veins, were not discovered until after his death.
In the late 19th century, physicians and laboratory scientists began to examine blood carefully. Bloodletting disappeared and researchers began to use blood for diagnosing disease. Over the past century, blood has been studied extensively, from cells to serum. The functions of thousands of proteins, lipids and carbohydrates have been identified. Blood cells have been examined on microscopic and submicroscopic levels. The knowledge has developed cures for many illnesses.
Blood was originally obtained through venipuncture, a procedure in which a needle pierces the vein and 5 to 10 ml of blood is drawn off. But in some patients the lab can cause anemia because so many tests are ordered.
In 1962, Dr. Robert Guthrie modified the test for a congenital disease, phenylketonuria. If the disease can be detected and treatment started soon after birth, the otherwise inevitable mental retardation will not occur. But the problem was drawing blood on every newborn. Dr. Guthrie developed a method of testing that only required a drop of dried blood on filter paper, obtained by pricking the baby's heel for a single drop.
Now hundreds of blood tests can be done using just one drop of blood instead of by a painful search for a vein. Not only does capillary blood sampling prevent pain and androgenic anemia, it does not require a professional and saves money. The patient can do it at home, making it easier for everyone. We've come a long way from leeches.
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