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. Know the possible causes of abnormal platelet counts.

What is a platelet count?

Why is it done?

Bleeding-petechiae

Functions of platelets

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

Technique

Platelets as seen on blood smears

Calculation

Sources of error

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?

Happy counting!