Platelets Function

Platelets, or thrombocytes, are solid components in the blood. At only 2-3 µm, they are the smallest cells in the blood and have an average lifespan of 8-12 days. Platelets are formed by strangulation of the megakaryocytes of the bone marrow. They have their function in hemostasis (blood clotting) by attaching themselves to the surrounding tissue when the blood vessel is injured (“platelet adhesion”) or sticking to each other (“platelet aggregation”), thus they close the injury. In addition, they release procoagulant substances in the process (secretion). Platelets can also increase inflammation: they cause macrophages (scavenger cells) and neutrophil granulocytes (a subgroup of leukocytes (white blood cells)) to form more inflammasomes. Inflammasomes are cytosolic multiprotein complexes of the innate immune system that are responsible for activating inflammatory responses.

The process

Material needed

  • 3 ml EDTA blood (determined as part of the small blood count); mix tubes thoroughly by swirling immediately after collection.

Preparation of the patient

  • Not necessary

Disruptive factors

  • Mix blood sample well

Normal value

Normal value in: Platelets/μl 150.000-400.000

Indications

  • Basic diagnostics of hematopoiesis (blood formation).

Interpretation

Interpretation of elevated values (thrombocytosis).

  • Bleeding, unspecified
  • Malignant neoplasms, unspecified (e.g., advanced tumors, Hodgkin’s disease, non-Hodgkin’s lymphoma (NDL))
  • Chronic infections: chronic tuberculosis, osteomyelitis.
  • Chronic inflammatory diseases: Crohn’s disease, ulcerative colitis, celiac disease, sarcoidosis, rheumatic fever.
  • Myeloproliferative neoplasms (MPN) (formerly chronic myeloproliferative diseases (CMPE)): eg.
    • Chronic myeloid leukemia (CML).
    • Osteomyelosclerosis (OMS)
    • Polycythaemia vera (PV; synonyms: polycythemia, polycythemia).
  • Post-splenectomy syndrome (synonyms: OPSI syndrome, English Overwhelming postsplenectomy infection syndrome) – special course of bacterial infection after splenectomy (surgical removal of the spleen).
  • Posttraumatic: operations, injuries, hemorrhages.
  • Regenerative: Z. n. severe bleeding, hemolytic anemia, bone marrow suppression (cytostatics, radiotherapy).
  • Severe inflammation, unspecified

Interpretation of decreased values (thrombocytopenia (thrombocytopenia), < 150,000/μl).

  • Synthesis disorders – aplastic disorders: Fanconi syndrome; bone marrow damage (chemicals – eg, benzene -, infections (eg, HIV); cytostatic therapy, radiation therapy).
  • Bone marrow infiltrations (leukemias, lymphomas, bone marrow metastases).
  • Maturation disorders (e.g. megaloblastic anemia/pernicious anemia).
  • Increased peripheral turnover of platelets.
    • Disseminated intravascular coagulation; disseminated intravascular coagulation (DIC syndrome, abbreviated as DIC; consumption coagulopathy) – acute onset coagulopathy caused by excessive activation of coagulation.
    • Idiopathic thrombocytopenic purpura (ITP; Werlhof’s disease) – autoantibody-mediated disorder of platelets; incidence: 1-4%.
    • Hemolytic uremic syndrome (HUS) – usually occurring in children in the context of infections hemolytic anemia (anemia) with accompanying renal insufficiency (kidney weakness).
    • Hypersplenism – complication of splenomegaly; leads to an increase in functional capacity beyond the necessary level; as a result, there is excessive elimination of erythrocytes (red blood cells), leukocytes (white blood cells) and platelets (platelets) from the peripheral blood, so that pancytopenia (synonym: tricytopenia: reduction of all three cell series in the blood) occurs.
    • Systemic lupus erythematosus (SLE) – collagenosis affecting mainly the skin and many internal organs.
  • Chronic alcoholism
  • Gestational thrombocytopenia (pregnancy-related isolated thrombocytopenia; physiological decrease: approx. 10%); manifestation (first occurrence): II./III. Trimenon (third trimester); course: asymptomatic; about 5-8 % of all pregnancies platelet count < 150,000/μl.
  • HELLP syndrome (H = hemolysis/dissolution of erythrocytes (red blood cells) in the blood), EL = elevated liver enzymes, LP = low platelets); ICD-10 O14.2) – Special form of preeclampsia associated with blood count changes; incidence: 15-22%.
  • Spontaneous hemorrhage, unspecified.
  • Drug-induced thrombocytopenia (see under hematoxic drugs); incidence:

Further notes

  • In the presence of asymptomatic thrombocytopenia, the first step should be to exclude pseudothrombocytopenia. The interpretation thrombocytopenia is a laboratory finding. This is triggered by the fact that after blood sampling the platelets present in the hematology sample tube (EDTA blood) clump together – due to IgG-type autoagglutinins, which lead to agglutination of the platelets in vitro in the presence of the anticoagulant ethylenediaminetetraacetic acid (EDTA). Platelet clumping results in significantly fewer platelets being counted than are present in vivo. Clarification is performed by platelet determinations in citrate or heparin blood by microscopic image examination.
  • Note: The positive predictive values of thrombocytosis (> 400 x 109/l) for malignant (malignant) disease are very high, 11.6% in men and 6.2% in women.
  • In case of changes in the platelet count or condition after myocardial infarction (heart attack), the mean platelet volume (MPV) can be determined.
  • Test for differential diagnosis in thrombocytopenia: determination of the proportion of immature platelets (% IPF) from the blood count:
    • Bone marrow failure: immature platelets not increased (lack of new production).
    • Increased platelet consumption: immature platelets increased.
  • Basic laboratory chemistry tests in thrombocytopenia:
    • CBC with reticulocyte count [V. a. infection: lymphocytosis, neutropenia, toxic granulation].
    • Direct antiglobulin/Coombs test
    • Liver and thyroid function tests
    • Virological diagnostics (e.g. HIV, HBV, HCV, CMV)
  • Advanced diagnostics:
    • Antinuclear antibodies (ANA)
    • Antiphospholipid antibodies (including lupus anticoagulant).
    • Exclusion of von Willebrand syndrome type 2B or defective of VWF-cleaving protease.
  • There is an increased tendency to bleed when the platelet count is less than 150,000/μl. Spontaneous skin bleeding may occur at platelet counts of 30-20,000/μl and spontaneous bleeding at levels below 10,000/μl.
  • In patients, especially with acute leukemia, prophylactic transfusion of platelets (platelet transfusion) below a threshold of 10,000/μl is the accepted standard.