Complete Blood Count, Platelet Count

Synonym/acronym: Thrombocytes.

Common use

To assist in diagnosing and evaluating treatment for blood disorders such as thrombocytosis and thrombocytopenia and to evaluate preprocedure or preoperative coagulation status.

Specimen

Whole blood from one full lavender-top (EDTA) tube.

Normal findings

(Method: Automated, computerized, multichannel analyzers)

Age	Platelet Count*	SI Units (Conventional Units × 1)	MPV (fL)	IPF (%)
Newborn
Male	150−350 × 10³/microL	150−350 × 10⁹/L	7.1–10.2	1.1–7.1
Female	235–345 × 10³/microL	235–345 × 10⁹/L	7.3–10.2	1.1–7.1
1–2 mo
Male	275–565 × 10³/microL	275–565 × 10⁹/L	7.1–11.3	1.1–7.1
Female	295–615 × 10³/microL	295–615 × 10⁹/L	7.4–9.7	1.1–7.1
3–6 mo
Male	275–565 × 10³/microL	275–565 × 10⁹/L	6.8–9.1	1.1–7.1
Female	288–598 × 10³/microL	288–598 × 10⁹/L	7.2–8.9	1.1–7.1
7–23 mo
Male	220–450 × 10³/microL	220–450 × 10⁹/L	7.1–9.3	1.1–7.1
Female	230–465 × 10³/microL	230–465 × 10⁹/L	7.1–9.3	1.1–7.1
2–6 yr
Male & Female	205–405 × 10³/microL	205–405 × 10⁹/L	7.1–9.3	1.1–7.1
7–12 yr
Male	195–365 × 10³/microL	195–365 × 10⁹/L	7.2–9.4	1.1–7.1
Female	185–370 × 10³/microL	185–370 × 10⁹/L	7.1–9.2	1.1–7.1
12–18 yr
Male	165–332 × 10³/microL	165–332 × 10⁹/L	7.3–9.7	1.1–7.1
Female	185–335 × 10³/microL	185–335 × 10⁹/L	7.5–9.3	1.1–7.1
Adult/Older adult
Male & Female	150−450 × 10³/microL	150−450 × 10⁹/L	7.1−10.2	1.1–7.1

Note: Platelet counts may decrease slightly with age.*Conventional units.MPV = mean platelet volume.

Description

Platelets are nonnucleated, cytoplasmic, round or oval disks formed by budding off of large, multinucleated cells (megakaryocytes). Platelets have an essential function in coagulation, hemostasis, and blood thrombus formation. Activated platelets release a number of procoagulant factors, including thromboxane, a very potent platelet activator, from storage granules. These factors enter the circulation and activate other platelets and the cycle continues. The activated platelets aggregate at the site of vessel injury, and at this stage of hemostasis the glycoprotein IIb/IIIa receptors on the activated platelets bind fibrinogen, causing the platelets to stick together and form a plug. Coagulation must be localized to the site of vessel wall injury, or the growing platelet plug would eventually occlude the affected vessel. The fibrinolytic system, under normal circumstances, begins to work, once fibrin begins to form, to ensure coagulation is limited to the appropriate site. Thrombocytosis is an increase in platelet count. In reactive thrombocytosis, the increase is transient and short-lived, and it usually does not pose a health risk. One exception may be reactive thrombocytosis occurring after coronary bypass surgery. This circumstance has been identified as an important risk factor for postoperative infarction and thrombosis. The term thrombocythemia describes platelet increases associated with chronic myeloproliferative disorders; thrombocytopenia describes platelet counts of less than 140 × 10³/microL. Decreased platelet counts occur whenever the body’s need for platelets exceeds the rate of platelet production; this circumstance will arise if production rate decreases or platelet loss increases. The severity of bleeding is related to platelet count as well as platelet function. Platelet counts can be within normal limits, but the patient may exhibit signs of internal bleeding; this circumstance usually indicates an anomaly in platelet function. Abnormal findings by automated cell counters may indicate the need to review a smear of peripheral blood for platelet estimate. Abnormally large or giant platelets may result in underestimation of automated counts by 30% to 50%. A large discrepancy between the automated count and the estimate requires that a manual count be performed. Platelet clumping may result in the underestimation of the platelet count. Clumping may be detected by the automated cell counter or upon microscopic review of a blood smear. A citrated platelet count, performed on a specimen collected in a blue-top tube, can be performed to obtain an accurate platelet count from patients who demonstrate platelet clumping in EDTA-preserved samples.

Thrombopoiesis or platelet production is reflected by the measurement of the immature platelet fraction (IPF). This parameter can be correlated to the total platelet count in the investigation of platelet disorders. A low platelet count with a low IPF can indicate a disorder of platelet production (e.g., drug toxicity, aplastic anemia or bone marrow failure of another cause), whereas a low platelet count with an increased IPF might indicate platelet destruction or abnormally high platelet consumption (e.g., mechanical destruction, disseminated intravascular coagulation [DIC], idiopathic thrombocytopenic purpura [ITP], thrombotic thrombocytopenic purpura [TTP]).

Platelet size, reflected by mean platelet volume (MPV), and cellular age are inversely related; that is, younger platelets tend to be larger. An increase in MPV indicates an increase in platelet turnover. Therefore, in a healthy patient, the platelet count and MPV have an inverse relationship. Abnormal platelet size may also indicate the presence of a disorder. MPV and platelet distribution width (PDW) are both increased in ITP. MPV is also increased in May-Hegglin anomaly, Bernard-Soulier syndrome, myeloproliferative disorders, hyperthyroidism, and pre-eclampsia. MPV is decreased in Wiskott-Aldrich syndrome, septic thrombocytopenia, and hypersplenism.

Platelets have receptor sites that are essential for normal platelet function and activation. Drugs such as clopidogrel, abciximab (Reopro), eptifibatide (Integrilin), and tirofiban block these receptor sites and inhibit platelet function. Aspirin also can affect platelet function by the irreversible inactivation of a crucial cyclooxygenase (COX) enzyme. Medications like clopidogrel (Plavix) and aspirin are prescribed to prevent heart attack, stroke, and blockage of coronary stents. Studies have confirmed that up to 30% of patients receiving these medications may be nonresponsive. There are several commercial test systems that can assess platelet function and provide information that confirms platelet response. Platelet response testing helps ensure alternative or additional platelet therapy is instituted, if necessary. The test results can also be used preoperatively to determine whether antiplatelet medications have been sufficiently cleared from the patient’s circulation such that surgery can safely be performed without risk of excessive bleeding. Thromboxane A2 is a potent stimulator of platelet activation. 11-dehydrothromboxane B2 is the stable, inactive product of thromboxane A2 metabolism, released by activated platelets. Urine levels of 11-dehydrothromboxane B2 can be used to monitor response to aspirin therapy.

The metabolism of many commonly prescribed medications is driven by the cytochrome P450 (CYP450) family of enzymes. Genetic variants can alter enzymatic activity that results in a spectrum of effects ranging from the total absence of drug metabolism to ultrafast metabolism. Impaired drug metabolism can prevent the intended therapeutic effect or even lead to serious adverse drug reactions. Poor metabolizers (PM) are at increased risk for drug-induced side effects due to accumulation of drug in the blood, while ultra-rapid metabolizers (UM) require a higher than normal dosage because the drug is metabolized over a shorter duration than intended. Other genetic phenotypes used to report CYP450 results are intermediate metabolizer (IM) and extensive metabolizer (EM). CYP2C19 is a gene in the CYP450 family that metabolizes drugs such as clopidogrel (Plavix). Genetic testing can be performed on blood samples submitted to a laboratory. Testing for the most common genetic variants of CYP2C19 is used to predict altered enzyme activity and anticipate the most effective therapeutic plan. The test method commonly used is polymerase chain reaction. Counseling and informed written consent are generally required for genetic testing.

This procedure is contraindicated for

N/A

Indications

Confirm an elevated platelet count (thrombocytosis), which can cause increased clotting
Confirm a low platelet count (thrombocytopenia), which can be associated with bleeding
Identify the possible cause of abnormal bleeding, such as epistaxis, hematoma, gingival bleeding, hematuria, and menorrhagia
Provide screening as part of a complete blood count (CBC) in a general physical examination, especially upon admission to a health-care facility or before surgery

Potential diagnosis

Increased in

Conditions that involve inflammation activate and increase the number of circulating platelets:
Acute infections
After exercise (transient)
Anemias (posthemorrhagic, hemolytic, iron-deficiency) (bone marrow response to anemia; platelet formation is unaffected by iron deficiency)
Chronic heart disease
Cirrhosis
Essential thrombocythemia
Leukemias (chronic)
Malignancies (carcinoma, Hodgkin’s, lymphomas)
Pancreatitis (chronic)
Polycythemia vera (hyperplastic bone marrow response in all cell lines)
Rebound recovery from thrombocytopenia (initial response)
Rheumatic fever (acute)
Rheumatoid arthritis
Splenectomy (2 mo postprocedure) (normal function of the spleen is to cull aging cells from the blood; without the spleen, the count increases)
Surgery (2 wk postprocedure)
Trauma
Tuberculosis
Ulcerative colitis

Decreased in

Decreased in (as a result of megakaryocytic hypoproliferation)

Decreased in (as a result of ineffective thrombopoiesis)

₁₂

Decreased in (as a result of bone marrow replacement)

Increased in

Increased destruction in (as a result of increased loss/consumption)

Contact with foreign surfaces (dialysis membranes, artificial organs, grafts, prosthetic devices)
Disseminated intravascular coagulation
Extensive transfusion
Severe hemorrhage
Thrombotic thrombocytopenic purpura
Uremia

Increased destruction in (as a result of immune reaction)

Antibody/human leukocyte antigen reactions
Hemolytic disease of the newborn (target is platelets instead of RBCs)
Idiopathic thrombocytopenic purpura
Refractory reaction to platelet transfusion

Increased destruction in (as a result of immune reaction secondary to infection)

Bacterial infections
Burns
Congenital infections (cytomegalovirus, herpes, syphilis, toxoplasmosis)
Histoplasmosis
Malaria
Rocky Mountain spotted fever

Increased destruction in (as a result of other causes)

Radiation
Splenomegaly caused by liver disease

Critical findings

Less than 30 × 10³/microL (SI: Less than 30 × 10⁹/L)
Greater than 1,000 × 10³/microL (SI: Greater than 1,000 × 10⁹/L)
Consideration may be given to verifying the critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid Point of Care instrument at the bedside.
Note and immediately report to the health-care provider (HCP) any critically increased or decreased values and related symptoms.
It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.
Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.
Critically low platelet counts can lead to brain bleeds or GI hemorrhage, which can be fatal. Some signs and symptoms of decreased platelet count include spontaneous nose bleeds or bleeding from the gums, bruising easily, prolonged bleeding from minor cuts and scrapes, or bloody stool. Possible interventions for decreased platelet count may include transfusion of platelets or changes in anticoagulant therapy.

Interfering factors

Drugs that may decrease platelet counts include acetohexamide, acetophenazine, amphotericin B, antazoline, anticonvulsants, antimony compounds, apronalide, arsenicals, azathioprine, barbiturates, benzene, busulfan, butaperazine, chlordane, chlorophenothane, chlortetracycline, dactinomycin, dextromethorphan, diethylstilbestrol, ethinamate, ethoxzolamide, floxuridine, hexachlorobenzene, hydantoin derivatives, hydroflumethiazide, hydroxychloroquine, iproniazid, mechlorethamine, mefenamic acid, mepazine, miconazole, mitomycin, nitrofurantoin, novobiocin, nystatin, phenolphthalein, phenothiazine, pipamazine, plicamycin, procarbazine, pyrazolones, streptomycin, sulfonamides, tetracycline, thiabendazole, thiouracil, tolazamide, tolazoline, tolbutamide, trifluoperazine, and urethane.
Drugs that may increase platelet counts include glucocorticoids.
X-ray therapy may also decrease platelet counts.
The results of blood counts may vary depending on the patient’s position. Platelet counts can decrease when the patient is recumbent, as a result of hemodilution, and can increase when the patient rises, as a result of hemoconcentration.
Platelet counts normally increase under a variety of stressors, such as high altitudes or strenuous exercise.
Platelet counts are normally decreased before menstruation and during pregnancy.
Leaving the tourniquet in place for longer than 60 sec can affect the results.
Traumatic venipunctures may lead to erroneous results as a result of activation of the coagulation sequence.
Failure to fill the tube sufficiently (i.e., tube less than three-quarters full) may yield inadequate sample volume for automated analyzers and may be a reason for specimen rejection.
Hemolysis or clotted specimens are reasons for rejection.
CBC should be carefully evaluated after transfusion or acute blood loss because the value may appear to be normal.

Nursing Implications and Procedure

Potential nursing problems

Problem	Signs & Symptoms	Interventions
Protection (Related to decreased platelet count; bleeding risk)	Ease of bruising; blood in urine, stool, sputum, nosebleed, bleeding gums; presence of hematoma or petechiae; headache; vision changes	Assess for brusing, petechiae, hematoma; monitor and trend platelet count; administer blood or blood products, platelets; administer stool softeners; administer prescribed corticosteroids; increase frequency of vital sign assessment with variances in results; monitor for vital sign trends; assess stool, urine, sputum, gums, nose, for blood; coordinate laboratory draws to decrease frequency of venipuncture; institute bleeding precautions avoid IM injections, prevent trauma, be gentle with oral care and suctioning avoid use of a sharp razor); administer prescribed medications (IV immunoglobulin, recombinant interleukin, anti-D immune globulin)
Tissue perfusion (cerebral, peripheral, renal) (Related to altered blood flow associated with platelet clumping)	Confusion; altered mental status; headaches; dizziness; visual disturbances; hypotension; cool extremities; capillary refill greater than 3 sec; weak pedal pulses; altered level of consciousness; decreased urine output	Monitor blood pressure; assess for dizziness; check skin temperature for warmth; assess capillary refill; assess pedal pulses; monitor level of consciousness; monitor urine output to be in excess of 30 mL/hr; ensure adequate fluid intake or administer intravenous fluids as ordered
Pain (Related to joint disturbances associated with bleeding; bleeding into the tissues)	Expression of pain, facial grimace, moaning, crying; report of pain	Assess level of pain and identify pain characteristics (what makes it better or worse); use a foot cradle to keep pressure off of legs; support joints with pillows; use socks to keep feet warm; administer prescribed analgesics; assess effectiveness of analgesics and collaborate with HCP to provide adequate pain management
Confusion (Related to decreased tissue perfusion secondary to platelet clumping and altered blood flow)	Disorganized thinking, restless, irritable, altered concentration and attention span, changeable mental function over the day, hallucinations; altered attention span; inability to follow directions; disoriented to person, place, time, and purpose; inappropriate affect	Treat the medical condition; monitor and trend platelet count; evaluate medications; prevent falls and injury through appropriate use of postural support, bed alarm, or restraints; administer prescribed medications (IV immunoglobulin, recombinant interleukin, anti-D immune globulin)

Pretest

Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
Patient Teaching: Inform the patient this test can assist in diagnosing, evaluating, and monitoring bleeding disorders.
Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
Obtain a history of the patient’s hematopoietic and immune systems, especially any bleeding disorders and other symptoms, as well as results of previously performed laboratory tests and diagnostic and surgical procedures.
Note any recent procedures that can interfere with test results.
Obtain a list of the patient’s current medications, including anticoagulants, aspirin and other salicylates, herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

Potential complications: N/A
Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture. The specimen should be mixed gently by inverting the tube 10 times. The specimen should be analyzed within 24 hr when stored at room temperature or within 48 hr if stored at refrigerated temperature. If it is anticipated the specimen will not be analyzed within 24 hr, two blood smears should be made immediately after the venipuncture and submitted with the blood sample.
Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
The results of a CBC should be carefully evaluated during transfusion or acute blood loss because the body is not in a state of homeostasis and values may be misleading. Considerations for draw times after transfusion include the type of product, the amount of product transfused, and the patient’s clinical situation. Generally, specimens collected an hour after transfusion will provide an acceptable reflection of the effects of the transfused product. Measurements taken during a massive transfusion are an exception, providing essential guidance for therapeutic decisions during critical care.
Nutritional Considerations: Instruct patients to consume a variety of foods within the basic food groups, maintain a healthy weight, be physically active, limit salt intake, limit alcohol intake, and avoid the use of tobacco.
Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.
Patient Education
- Instruct the patient to report bleeding from any areas of the skin or mucous membranes.
- Inform the patient of the importance of periodic laboratory testing if he or she is taking an anticoagulant.
- Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP
- Answer any questions or address any concerns voiced by the patient or family.
Expected Patient Outcomes
- Knowledge
- States the importance of taking a stool softener to prevent straining while having a bowel movement
- States the importance of taking precautions against bruising and bleeding, including the use of a soft bristle toothbrush, use of an electric razor, avoidance of constipation, avoidance of acetylsalicylic acid and similar products, and avoidance of intramuscular injections
- Skills
- Identifies symptoms of bleeding that should be reported to the HCP
- Identifies pain management therapy that provides the best pain relief
- Attitude
- Complies with the request to refrain in participating in at-risk activities that could cause trauma and bleeding
- Complies with the request to take stool softeners to prevent constipation and bleeding

Related Monographs

Related tests include antiarrhythmic drugs (quinidine), biopsy bone marrow, bleeding time, blood groups and antibodies, clot retraction, coagulation factors, CBC, CBC RBC morphology and inclusions, CBC WBC count and differential, CT angiography, CT brain, FDP, fibrinogen, PTT, platelet antibodies, procalcitonin, PT/INR, and US pelvis.
Refer to the Hematopoietic and Immune systems tables at the end of the book for related tests by body system.

Complete Blood Count, Platelet Count