Thrombocytopenia Purpura (Low Platelets) – ITP, TTP, HUS, Heparin

The body has several mechanisms to stop bleeding collectively known as hemostasis. This involves multiple phases, each with several processes which ultimately stops blood loss and allows the body the opportunity to repair the damaged blood vessel. In certain diseases, these mechanisms are compromised giving rise to some of the more well known bleeding disorders like hemophilia. Another type of bleeding disorder is thrombocytopenia purpura often referred to just as thrombocytopenia.

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What is thrombocytopenia?

Thrombocytopenia purpura (TP) is a bleeding disorder characterized by a very low number of platelets (thrombocytes) circulating in the blood stream. While the aggregation of platelets are an important phase of hemostasis on its own which can plug small holes and stop bleeding, the activation of these platelets is also important to mediate further phases of hemostasis. The coagulation phase that follows the formation of a platelet plug depends on the activity of the accumulated platelets to then allow for the formation of a blood clot.

If the platelet numbers are low or not functioning optimally, both the platelet and coagulation phase of hemostasis is compromised. As is seen in the coagulation cascade, there are several clotting factors that require the activity of platelet phospholipids in order to be activated and mediate further steps in the cascade.

Low Platelet Levels

There is approximately 150,000 to 450,000 platelets per microliter (uL) in the human blood and these numbers are sufficient to plug the micro-tears that occur at several points of the vascular system in any given day. It occurs even without trauma but bleeding is usually so minor and the action of hemostatic mechanisms so efficient that it goes by unnoticed. However, with bleeding disorders like thrombocytopenia, the low level of platelets does not allow for rapid action and spontaneous healing. Therefore a person will exhibits signs and symptoms of hemorrhage ( bleeding) even without any significant injury. This can occur once the platelets fall below 50,000 platelets per microliter and even minor trauma results in bleeding. Once the platelet level drops to as low as 10,000 / uL, bleeding can be spontaneous and at this level the condition can be fatal.

Causes and Types of Thrombocytopenia

There are several different types of thrombocytopenia classified according to the cause. In some cases large numbers of platelets are destroyed, while in other situations the body utilizes excessive platelets often unnecessarily thereby removing these platelets from circulation. Thrombocytopenia may arise secondary to other diseases that reduce platelet production, cause platelets to become entrapped in the enlarged spleen or when the platelet concentration in the blood is diluted.

Idiopathic Thrombocytopenia Purpura (ITP)

As the name suggest, this type of thrombocytopenia occurs for no known reason. Antibodies formed by the body against the platelets (auto-antibodies) attach to the platelet membranes. This “marks” the platelets for destruction by the body’s immune system particularly within the spleen. In idiopathic thrombocytopenia purpura (ITP) the body still produces a normal level of platelets but these are rapidly removed from the circulation thereby leading to a platelet deficiency. This type of thrombocytopenia is seen with immune dysfunction often associated with diseases like HIV infection and autoimmune disorders. It may also occur in pregnancy and with the use of certain drugs like heparin.

Heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) may arise after the administration of unfractionated heparin. This drug is an anticoagulant and when derived from natural sources (unfractionated) compared to synthetic formulas of lower molecular weight, the effects can sometimes be unpredictable. Antibodies are then formed against the heparin and certain platelet proteins which then attach to and activate the platelets. These platelets are then removed from the circulation thereby leading to a deficiency of platelets.

Thrombotic Thrombocytopenia Purpura (TTP)

In this type of thrombocytopenia, there is sudden formation of blood clots throughout the body even though there is no hemorrhage (bleeding) requiring clot formation. In the process, the circulating platelet levels drop because the body uses the platelets to form these clots.

Hemolytic-Uremic Syndrome (HUS)

Toxins produced in the gut by bacteria like E.coli are absorbed into the bloodstream where it triggers the rapid destruction of red blood cells and platelets. The patient usually has gastroentritis associated with E.coli infection and this conditions may also occur with other infections like Shigellosis.

Other Causes of Low Platelet Count

Platelet levels may also be low due to decreased production in the bone marrow as is seen with :

  • Alcohol abuse
  • Leukemia
  • Lymphoma
  • Aplastic anemia and other types of anemia

In the event of splenomegaly (enlarged spleen), platelets in the circulation may become trapped within the spleen. Therefore the platelet levels in circulation drop substantially.

Another situation where circulating platelet levels may be low is seen in massive transfusions or following major surgery.

Signs and Symptoms of Thrombocytopenia

In thrombocytopenia, there is a tendency to bleed just as with other bleeding disorders like hemophilia. The bleeding (hemorrhage) occurs more commonly in the small blood vessels and capillaries and often appears as tiny spots of bleeding (petechiae) of around 1mm to 2mm on the skin and mucous membranes.

Less frequently, larger spots of bleeding underneath the skin (ecchymosis) may also be seen immediately after an injury. In most cases there is easy bruising and bleeding following even minor trauma. However, once the number of platelets falls to dangerously low levels, there may be spontaneous bleeding.

Patients may also report spontaneous nosebleeds (epistaxis) or menorrhagia (heavy menstrual bleed). There may be detectable levelsĀ  of blood in the stool (hematuria) and/or urine (melena / hematochezia). Profuse bleeding from even minor cuts is also reported although it may not always be as prominent in mild thrombocytopenia. There is a tendency to bleed excessively during and after surgery including in dental procedures.

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