2Objectives 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.
7Why 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.
9Brecher –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
18Precautions 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.
19Precautions 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 .
20Conditions affecting number of platelets in blood Thrombocytopenialow platelet countThrombocytosishigh platelet count
21Thrombocytopenia (low platelet count) CausesReduced production of plateletsIncreased breakdown of plateletsTrapping of platelets in the spleen
22Thrombocytopenia (low platelet count) As a result ofa bone marrow disorder such as leukemiaan immune system malfunctionas 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.
23Reduced production of platelets leukemiasome types of anemia,Viral infections,cancers that affect bone marrow,chemotherapy drugsheavy alcohol consumption
24Increased breakdown of platelets PregnancyIdiopathic 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
25Trapping of platelets in the spleen may harbor too many platelets, causing a decrease in the number of platelets in circulation.
26Signs and symptoms of a low blood platelet count may include: Easy or excessive bruisingSuperficial bleeding into the skin that appears as a rash of pinpoint-sized reddish-purple spots (petechiae), usually on the lower legsProlonged bleeding from cutsSpontaneous bleeding from gums or noseBlood in urine or stoolsUnusually heavy menstrual flowsProfuse bleeding during surgerySerious or widespread bleeding indicates an emergency and requires immediate care.
27Thrombocytosis (high platelet levels ) reaction to an infectionsurgerycertain medicationsPolycythemia vera, in which the bone marrow produces too many platelets too quickly.
28QuestionsWhy 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?
29QuestionsWhy 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?