Fundamentals of Nursing Q 258
Which of the following blood tests should be performed before a blood transfusion?
A. Prothrombin and coagulation time
B. Blood typing and cross-matching
C. Bleeding and clotting time
D. Complete blood count (CBC) and electrolyte levels
Correct Answer: B. Blood typing and cross-matching
Before a blood transfusion is performed, the blood of the donor and recipient must be checked for compatibility. This is done by blood typing (a test that determines a person’s blood type) and cross-matching (a procedure that determines the compatibility of the donor’s and recipient’s blood after the blood types have been matched). If the blood specimens are incompatible, hemolysis and antigen-antibody reactions will occur. If the donor is eligible to donate, the donated blood is tested for blood type (ABO group) and Rh type (positive or negative). This is to make sure that patients receive blood that matches their blood type. Before transfusion, the donor and blood unit are also tested for certain proteins (antibodies) that may cause adverse reactions in a person receiving a blood transfusion.
Option A: A prothrombin time (PT) is a test used to help detect and diagnose a bleeding disorder or excessive clotting disorder. A PT measures the number of seconds it takes for a clot to form in your sample of blood after substances (reagents) are added. The PT is often performed along with a partial thromboplastin time (PTT) and together they assess the amount and function of proteins called coagulation factors that are an important part of proper blood clot formation. The coagulation time is a measurement of the intrinsic power of the blood to convert fibrinogen to fibrin. It is an empirical test no matter how performed, and therefore in order to be reliable requires that the test be done on venous blood under strictly controlled conditions.
Option C: Bleeding time is a laboratory test to assess platelet function and the body’s ability to form a clot. The test involves making a puncture wound in a superficial area of the skin and monitoring the time needed for bleeding to stop (ie, the bleeding site turns “glassy”). The expected range for clotting time is 4-10 mins. This test measures the time taken for blood vessel constriction and platelet plug formation to occur. No clot is allowed to form, so that the arrest of bleeding depends exclusively on blood vessel constriction and platelet action.
Option D: The complete blood count (CBC) is a group of tests that evaluate the cells that circulate in the blood, including red blood cells (RBCs), white blood cells (WBCs), and platelets (PLTs). The CBC can evaluate your overall health and detect a variety of diseases and conditions, such as infections, anemia, and leukemia.