Platelets may be counted manually or with electronic counting devices. Although larger numbers of platelets are capable of being examined with electronic counting, the procedure is subject to error if (1) the white blood cell (WBC) count is greater than 10,000 cells per cubic millimeter, (2) there is severe red blood cell fragmentation, (3) the diluting fluid contains extraneous particles, (4) the plasma sample settles too long during processing, or (5) platelets adhere to one another.

Causes of increased numbers of platelets (thrombocytosis, thrombocythemia) and decreased numbers of platelets (thrombocytopenia) are presented in Table 2-3.

Mean platelet volume can also be determined by the electronic automated method. The test reveals the size of platelets important in the diagnosis of disorders affecting the hematologic system. An increased volume of platelets that are larger than normal in diameter is found in lupus erythematosus, thrombocytopenic purpura, B₁₂-deficiency anemia, hyperthyroidism, and myelogenic and other myeloproliferative diseases. A decreased volume of the larger sized platelets is found in Wiskott-Aldrich syndrome.²²

• Altered test results may occur if:
  • The WBC count is greater than 100,000 per cubic millimeter.
  • There is severe red blood cell fragmentation.
  • The fluid used to dilute the sample contains extraneous particles.
  • The plasma sample settles too long during processing.
  • Platelets adhere to one another.
  • The client is receiving drugs that alter platelet functions and numbers (see Tables 2-2 and 2-3).
• Traumatic venipunctures may lead to erroneous results as a result of activation of the coagulation sequence.
• Excessive agitation of the sample may cause the platelets to clump together and adhere to the walls of the test tube, thus altering test results.

• Family history of bleeding disorder
• Signs of abnormal bleeding such as epistaxis, easy bruising, bleeding gums, hematuria, and menorrhagia
• Determination of effects of diseases and drugs known to alter platelet levels (see Table 2-3)
• Identification of individuals who may be prone to bleeding during surgical, obstetric, dental, or invasive diagnostic procedures, as indicated by a platelet count of approximately 50,000 to 100,000 per cubic millimeter
• Identification of individuals who may be prone to spontaneous bleeding, as indicated by a platelet count of less than 15,000 to 20,000 per cubic millimeter
• Differentiation between decreased platelet production and decreased platelet function:
  • Platelet dysfunction is defined as a long bleeding time with a platelet count of greater than 100,000/mm³.²³

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

A venipuncture is performed and the sample collected in a lavender-topped tube. A capillary sample may be obtained in infants and children as well as in adults for whom venipuncture may not be feasible.

Nursing Care After the Procedure

Care and assessment after the procedure are essentially the same as for any study involving the collection of a peripheral blood sample. Because the client may have a platelet deficiency, maintain digital pressure directly on the puncture site for 3 to 5 minutes after the needle is withdrawn. Also, inspect the site for excessive bruising after the procedure.

• Abnormal increase (thrombocytosis): Note and report signs of dehydration and input and output (I&O) ratio that can contribute to venous stasis, possible thrombosis, or bleeding tendency if the coagulation process is affected. Administer ordered aspirin and antacid, and observe for bleeding tendency if prothrombin time is increased.
• Abnormal decrease (thrombocytopenia): Note and report petechiae, bruising, or hematoma. Administer ordered corticosteroids. Protect children from trauma, advise adults to use soft toothbrushes and electric razors, and prevent other trauma by padding side rails and avoiding intramuscular and subcutaneous injections. Assess bleeding from skin and mucous membranes (petechiae, ecchymoses, epistaxis, feces, urine, emesis, sputum). Administer platelet transfusion and assess for any allergic responses, sepsis, or hypervolemia.
• Critical values: Notify the physician immediately if the platelet count is less than 20,000/mL or greater than 1 million/mL. Prepare for transfusion of platelets by intravenous drip or bolus infusion.