If your doctor orders a blood examination, naturally the technician must obtain a specimen of your blood. The easiest source of this is the veins of your arms. From the patient’s standpoint, it is a simple procedure. It means the insertion of a needle into the vein, but this is just one sharp sting of the needle and the pain involved is hardly worth discussing.
Before the insertion of the needle a band will be placed around your upper arm to retard the return flow of blood in the veins; this makes the veins bulge for easy location. The skin is then cleaned with an antiseptic and the needle inserted. The blood is withdrawn, the needle is removed, and pressure is held over the site for a moment or two. The specimen is placed in a tube and allowed to clot or an anticoagulant is added, depending on the analysis to be made. The blood test may be ordered by your doctor for any one of many different determinations.
Inserting a needle into the vein is called veni- puncture.
Blood Counts and Hemoglobin Tests
Your doctor orders a blood count to determine the exact number of each type of cell contained in a unit volume of your blood. This test and the determination of the amount of hemoglobin in your blood are done in the same manner. For these tests, often very important in evaluating you for treatment, only a drop of blood is needed. It could be taken from any place. Occasionally it is taken from the lobe of the ear, from a toe, or from a vein, but the most common site is a finger tip. The technician will hold your finger, cleanse the skin with antiseptic, and give one quick puncture with the puncturing device. The exact amount of blood needed is then drawn up into a small glass pipet, and the technician proceeds to dilute the fraction of a drop in the pipet and will count the cells under a microscope. One pipet is for counting red blood cells, another is for counting the white cells and for the hemoglobin determination. A small drop of blood is spread over a glass slide for microscopic examination of the different blood cells. These tests make up what is referred to as the complete blood count, and together they take only a drop of blood. After the specimens are taken, pressure is held over the site of puncture on the finger tip for a few moments. The discomfort is slight and only momentary.
Bleeding and Clotting Tests
Occasionally the surgeon will want to test the patient’s blood for its ability to clot and stop bleeding. In some conditions, such as liver disease, blood disease, and malnutrition, the clotting mechanism is slowed. These tests are done at the bedside by obtaining a drop of blood from the finger tip just as in blood counts. The technician measures the time it takes for the bleeding to stop, and also the time required for a clot to form in a small capillary tube or other device.