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Platelet count. Objectives. To understand the importance of doing a platelet count To know the methods of performing a platelet count . To perform a platelet count . Know the possible sources of error and precautions to be taken in conducting a platelet count. Know the normal values.
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Objectives • To understand the importance of doing a platelet count • To know the methods of performing a platelet count . • To perform a platelet count . • Know the possible sources of error and precautions to be taken in conducting a platelet count. • Know the normal values. • Know the possible causes of abnormal platelet counts.
Why is platelet counting difficult? • They are small and difficult to discern. • Their adhesive character-attach readily to glassware, particles or debris in the diluting fluid. • They clump easily. • Not evenly distributed in the mixture of blood and diluting fluid. • They readily disintegrate in the blood diluted with fluid making it difficult to distinguish them from debris. Therefore unless carefully done ,accurate counting of platelets becomes impossible.
Methods • Haemocytometry (direct count) 1.Brecher-Cronkite method 2.Rees –Ecker method • Study of blood smear (indirect method) • Automated counting.
Brecher –Cronkite method Principle: The diluent contains Ammonium Oxalate. This completely lyses the red cells. the platelets are then counted with a phase –haemocytometer and phase contrast microscope to enhance the refractileness of the platelets.(or ordinary microscope) Advantage: • Identification is easier. • The error involved is low
Precautions to be taken • Glassware must be scrupulously cleaned . debris and dust are the main sources of error as they are easily mistaken for platelets. • The diluting fluid must be filtered just before use . to remove particles. • If venous blood is used the platelets must be counted within 3 hours. delay causes disintegration and clumping of platelets. • Blood should be rapidly diluted . this is essential to prevent clumping.
Precautions to be taken • Blood must be thoroughly mixed with the diluent by shaking the contents at least for 10 minutes. inadequate mixing results in clumping of platelets. • The charged chamber should be kept for 15 minutes under petri dish. to prevent evaporation and for the cells to settle down. • If other haematologic tests are to be done with platelet count ,and blood is used from the same puncture ,take blood for the platelet count first. • The finger should not be squeezed excessively to collect blood .
Conditions affecting number of platelets in blood • Thrombocytopenia low platelet count • Thrombocytosis high platelet count
Thrombocytopenia (low platelet count) Causes • Reduced production of platelets • Increased breakdown of platelets • Trapping of platelets in the spleen
Thrombocytopenia (low platelet count) As a result of • a bone marrow disorder such as leukemia • an immune system malfunction • as a reaction to a medication. Complications may range from none at all to severe bleeding. • The greatest risk is when platelet count falls very low <10,000 per microliter . internal bleeding may occur despite a lack of any injury.
Reduced production of platelets • leukemia • some types of anemia, • Viral infections, • cancers that affect bone marrow, • chemotherapy drugs • heavy alcohol consumption
Increased breakdown of platelets • Pregnancy • Idiopathic thrombocytopenic purpura (ITP), • Other autoimmune diseases, such as lupus and rheumatoid arthritis, • Septicemia severe bacterial infections, • Thrombotic thrombocytopenic purpura (TTP), a rare, life-threatening condition TTP can happen sporadically or as a side effect of some medications. • Hemolytic uremic syndrome, • Dengue fever
Trapping of platelets in the spleen • may harbor too many platelets, causing a decrease in the number of platelets in circulation.
Signs and symptoms of a low blood platelet count may include: • Easy or excessive bruising • Superficial bleeding into the skin that appears as a rash of pinpoint-sized reddish-purple spots (petechiae), usually on the lower legs • Prolonged bleeding from cuts • Spontaneous bleeding from gums or nose • Blood in urine or stools • Unusually heavy menstrual flows • Profuse bleeding during surgery • Serious or widespread bleeding indicates an emergency and requires immediate care.
Thrombocytosis(high platelet levels ) • reaction to an infection • surgery • certain medications • Polycythemia vera, in which the bone marrow produces too many platelets too quickly.
Questions • Why does the platelet count give inaccurate results unless performed carefully? • What are the different methods of platelet count? • What is the principle of the Brecher –Cronkite method? • Why is the reagent filtered before every use? • Why is venous blood preferred to capillary blood for platelet count? • Why is glassware cleaned thoroughly for platelet count?
Questions • Why is the blood rapidly diluted and thoroughly mixed with the diluting fluid? • Why is the charged chamber covered by a petridish for 15 minutes? • How do you identify platelets under the high power objective? • What are the sources of error in manual method of platelet count? • What is the normal platelet count? • What are the properties of platelets?what are their functions? • What are the causes of thrombocytosis and thrombocytopenia?
