Platelets – Part 1 – Idiopathic thrombocytopenic Purpura (ITP), Platelet Antibody (Anti-Platelet Antibody)

Sample

1. Plasma is needed.
2. Plasma is separated and frozen in a plastic tube.
3. Or collect the blood in acid citrate dextrose (ACD) solution.
4. Apply the pressure or do pressure dressing to stop the bleeding.

Precautions

1. Apply the pressure to the site of the blood sample.
2. If there is bleeding from the site then ask the patient to apply the pressure.

Indications

1. This test is indicated when there are low platelet counts.
2. In the case of unresponsive to the treatment of low platelets.

Pathophysiology

1. Platelets are mainly involved in the clotting mechanism.
2. Antiplatelet antibodies are found in the patient with idiopathic thrombocytopenic purpura (ITP) where the antigen is platelets.
3. Autoimmune (idiopathic) thrombocytopenic purpura may be divided into:
   1. Acute.
   2.  Chronic.
4. There is the immune-mediated destruction of the platelets.

4. The antibodies are usually directed against the HLA-antigen on the surface of platelets. Or maybe platelets specific antigen (PLA1 and PLA2)
5. Immunologic thrombocytopenia:
   1. This may due to the following causes:
      1. Idiopathic thrombocytopenic purpura (ITP). This is an autoimmune phenomenon and platelets are destroyed in the spleen or reticuloendothelial system.
         1. Chronic idiopathic thrombocytopenia:
            1. This is more common in the female aged 15 to 50 years.
            2. This is the most common cause without anemia and leucopenia.
            3. This is also seen in association with other diseases like systemic lupus erythematosus (SLE), HIV infection, chronic lymphocytic leukemia, Hodgkin’s disease, or autoimmune hemolytic anemia.
         2. Platelets associated with antibodies (Immunoglobulin IGg) are found in 90% of the cases.
      2. Post-transfusion purpura. 
         1. This is a rare phenomenon seen after a blood transfusion and may be seen within a few hours to a few days.
         2. It is usually seen around the 10th day of the transfusion.
         3. This will develop due to antibodies in the recipient developing against platelet antigen-1a (HPA-1a) absent from the patient’s own platelets on transfused platelets.
         4. Treatment is by giving intravenous immunoglobulin, plasma exchange, or corticosteroids.
      3. Maternal-fetal platelet incompatibility.
         1. This usually occurs when the fetus has PLA1 and the mother is lacking this antigen. Mothers develop antibodies and this Antibody can cross the placental barrier and give rise to neonatal thrombocytopenia.
   2. Drug-induced thrombocytopenia. This is due to the hypersensitivity reaction to drugs. e.g. Cimetidine, analgesics like salicylate and acetaminophen, antibiotics (cephalosporin, penicillin, sulphonamide), quinidine drugs, oral hypoglycemic agents, heavy metal ( gold, organic arsenical), diuretics (chlorothiazide), digoxin, heparin, and propylthiouracil.

Other classification of thrombocytopenia:

1. Increased platelets destruction:
   1. Primary immune mechanism:
      1. Idiopathic thrombocytopenic purpura (ITP).
      2. Post transfusional purpura.
      3. Neonatal isoimmune purpura.
      4. Drug-induced thrombocytopenia.
   2. Secondary immune mechanism:
      1. Lymphoproliferative disorder.
      2. Autoimmune disease SLE.
      3. Viral infections like infectious mononucleosis, HIV, and measles.
      4. Hemolytic uremic syndrome.
      5. Disseminated intravascular coagulopathy (DIC).
      6. Microangiopathic thrombocytopenia.
      7. Pregnancy-associated thrombocytopenia.
2. Abnormal platelets destruction:
   1. Splenomegaly leading to hypersplenism.
   2. Hemangiomas.
3. Decreased production of the platelets:
   1. Lymphomas.
   2. Leukemias.
   3. Metastatic carcinoma infiltration of the bone marrow.
   4. Myelofibrosis.
   5. Aplastic anemia.
   6. Pernicious anemia.
   7. Folic acid deficiency.

Symptoms of low platelets:

1. If there is a bruise or bleeding, it will take a longer time to stop.
2. Skin bruises easily.
3. In the female, there is heavy bleeding.
4. There are frequent nosebleeds.

Sign and symptom of  Idiopathic thrombocytopenic purpura (ITP)

1. In the beginning, there are nonspecific symptoms.
2. In young children, it may develop ITP within 1 to 3 weeks of the viral infection.
   1. The onset of symptoms is usually abrupt and usually count of <20,000 /cmm.
   2. The disease is usually self-limiting and there is spontaneous remission with or without therapy and this occurs in the majority of the cases.
3. In the adult, this is seen between the ages of 20 to 50 years and, more common in the females.
   1. There is no recent history of infection or drug therapy.
   2. Typically platelets <30,000/cmm and patient may have a bleeding tendency.
   3. Typically patients will have mucosal bleeding.
   4. The primary hemostatic defect is seen like menorrhagia, epistaxis, bruises, or petechiae.

Sign and symptom of Thrombotic thrombocytopenic purpura (TTP)

1. This is a rare and often fatal syndrome associated with low platelet count (thrombocytopenia).
   1. Then patients develop weakness, malaise, fatigue, and fever.
   2. The patient may develop abdominal pain.
      1. The patient may have abdominal pain, pancreatitis, and gastrointestinal bleeding.
   3. These patients may have neurologic and renal dysfunction.
      1. There may be a mild headache, and in some cases, patients may develop coma and seizures.
2. S/S severity is variable.
3. Fever is usually <38 °C.
4. The patient may develop proteinuria or hematuria and these signs are mild.

Possible Complication:

1. There is the possibility of bleeding.
2. There may be a bruise formation.
3. There is the possibility of infection.
4. Some patients may feel dizziness.

Normal

Platelets

	cmm	x109 / L   (SI unit)
Adult	15,000 to 400,000	150 to 400
Premature infants	100,000 to 300,000	100 to 300
Newborn	150,000 to 300,000	150 to 300
Infants	200,000 to 475,000	200 to 475
Children	150,000 to 400,000	150 to 400

• Platelet antibody 
  Negative

Increased levels of Ab seen in:

1. Immunologic thrombocytopenic purpura( ITP)
2. Neonatal thrombocytopenia.
3. Posttransfusion purpura.
4. Drug-induced thrombocytopenia.
5. Systemic lupus erythematosus.

Treatment of ITP

1. The count above 50,000/cmm does not require the treatment.
2. Steroids (corticosteroids)  are given in high doses.
   1. 80% of the patients respond and goes into remission.
      1. Prednisolone 1 mg/kg/day is the initial dose in the adult.
      2. The dose is gradually reduced to lower doses after 10 to 14 days.
   2. Splenectomy is the second choice.
      1. This is advised in patients who have count <30,000/cmm after the steroids for three months.
      2. Or in patients who are on high doses of steroids to maintain the count above 30,000/cmm.
   3. Immunoglobulins are given intravenous in high doses and there is a rapid increase in the platelet count.
      1. 400 mg/kg/day for 5 days or 1 gram/kg/day for 2 days.
   4. Immunosuppressant drugs like vincristine, cyclophosphamide, azathioprine, or cyclosporin alone or in combination.
   5. Platelets transfusion.
   6. Stem cell transplantation can be tried.

Critical value = <50,000/cmm or >one million /cmm.

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