Platelets - Kresser Institute Membership Site

Marker Name: Platelets

REFERENCE RANGES FOR PLATELETS:

Laboratory reference range: 150–379 x 10³/µL

Functional reference range: 150–379 x 10³/µL

DESCRIPTION:

Platelets are small, disc-shaped cells that are integral to the repair of damaged blood vessels. In the presence of injured vascular endothelium, platelets initiate and coordinate clot formation by adhering to the injured blood vessel, aggregating to form a platelet plug, and secreting factors that initiate the coagulation cascade.^1-3 Platelets can also recruit white blood cells and progenitor cells to sites of vascular injury.⁴

Platelets bind to proteins in the extracellular matrix that are exposed during blood vessel injury. Binding to these exposed proteins (e.g., collagen) activates the platelets, causing them to secrete various molecules, including thromboxane A2 and ADP. These molecules stimulate other platelets in the vicinity, which in turn activate those platelets. Activated platelets bind to circulating fibrinogen and enhance the action of thrombin; fibrinogen and thrombin are two major proteins involved in coagulation.⁵ Thrombin is also an extremely potent activator of platelets, which further enhances hemostasis.¹

Platelets are the direct products of megakaryocytes. Like all blood cell lines, megakaryocytes are produced from multipotent stem cells within the bone marrow.⁶ Megakaryocytes are released from the bone marrow and travel to the lung, where they are transformed into platelets.⁷ Megakaryocytes respond to the body’s need for platelets by altering their number and size, increasing or decreasing based on relative need.⁶ Platelet formation and megakaryocyte production are controlled by the hematopoietic cytokine thrombopoietin.⁸ The body attempts to regulate platelet mass rather than platelet number through megakaryocyte production and maturation, as well as thrombopoietin levels.⁶

The standard laboratory test for platelets is a platelet count, which reports total platelet number.⁹ Platelet morphology can be evaluated by a peripheral blood smear. Certain aspects of platelet function can be assessed by various studies including platelet aggregometry, bleeding time, thromboelastography, platelet-mediated thrombin generation, and platelet activation measurement.¹⁰ These tests can be used to evaluate platelet dysfunction or to monitor antiplatelet therapies.

Thrombocytosis is an abnormally high number of platelets in the blood.⁹ Thrombocytosis can occur in a variety of medical conditions. Elevated platelet counts are most commonly seen in the course of hematologic conditions, both cancer (e.g., lymphoma) and non-cancer disorders (e.g., iron-deficiency anemia). Various acute and chronic inflammatory conditions may increase platelet counts. These inflammatory conditions may be the result of a chronic infection or primary rheumatologic condition, such as rheumatoid arthritis.¹¹ Thrombocytosis may be a reaction to bodily injury such as thermal burns, severe trauma, or major surgery.¹² Drugs in several drug classes can also increase platelet counts.

Thrombocytopenia is a condition in which platelet count is below normal.⁹ A low platelet count occurs in three broad circumstances: the bone marrow is not making enough platelets, platelets are being destroyed in the bloodstream, or the liver or spleen is removing platelets from circulation.⁹ Decreased production of platelets in the bone marrow may be due to myelodysplastic disorders, hematologic malignancies, aplastic anemia, metastatic cancer to bone marrow, or even treatment for cancer (chemotherapy, radiation).¹³ Platelets may be destroyed in various immune (e.g., heparin-induced thrombocytopenia) and nonimmune (e.g., disseminated intravascular coagulation) conditions. Five percent of women will have thrombocytopenia as part of normal pregnancy without any known sequelae. On the other hand, a fraction of pregnant women will develop a very serious condition called the HELLP syndrome, which stands for hemolysis, elevated liver function, and low platelets.¹⁴

A platelet count is a standard component of a complete blood count (CBC).¹⁵ Thus, a platelet count is determined along with a red blood cell count, a white blood cell count, hemoglobin and hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC). A peripheral blood smear should be used to confirm and investigate thrombocytosis or unexplained thrombocytopenia.¹²

PATHOLOGICAL/CONVENTIONAL RANGE INDICATIONS: High in:^9,12,16

Nonmalignant hematologic conditions
- Acute blood loss
- Acute hemolytic anemia
- Iron-deficiency anemia
- Treatment of vitamin B12 deficiency
Acute and chronic inflammatory conditions, including:
- Inflammatory bowel disease
- Celiac disease
- POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, skin changes)
- Rheumatologic disorder
- Vasculitis
- Chronic infections (e.g. ,tuberculosis)
Cancer (e.g., lymphoma)
Primary thrombocythemia
Tissue damage (e.g., severe trauma, severe burn, myocardial infarction, major surgery)
Asplenia (surgical or functional)
Spurious laboratory result
- Mixed cryoglobulinemia
- Pseudohyperkalemia
- Cytoplasmic fragments
Drug-induced thrombocytosis (e.g., vincristine, enoxaparin, thrombopoietin)

Low in:^13,14

Nutrient deficiencies (e.g., vitamin D, vitamin B12, folate, copper)
Pregnancy-related thrombocytopenia
- Normal pregnancy
- HELLP syndrome (hemolysis, elevated liver function, and low platelets)
- Preeclampsia
Autoimmune disorders and rheumatologic diseases
- Rheumatoid arthritis
- Antiphospholipid antibody syndrome
- Systemic lupus erythematosus
Infection (e.g., HIV, hepatitis C, Epstein-Barr virus, intracellular parasites, sepsis)
Aplastic anemia
Dilution (polydipsia, IV fluid administration)
Primary bone marrow disorder
Bone marrow infiltration by cancer
Hypersplenism or chronic liver disease
Congenital platelet disorders
Disseminated intravascular coagulation
Thrombotic thrombocytopenic purpura-hemolytic uremic syndrome
Idiopathic thrombocytopenic purpura
Paroxysmal nocturnal hemoglobinuria
Cardiac bypass
Post-transfusion purpura
Drug-induced thrombocytopenia
- Antiplatelet drugs (e.g., GPIIb/IIIa inhibitor, clopidogrel)
- Heparin
- NSAIDs
- Antibiotics (e.g., vancomycin, ampicillin)
- Chemotherapeutics

FUNCTIONAL RANGE INDICATIONS:

High in:

Same as conventional indications

Low in:

Same as conventional indications

References: