Thrombocytopenia is defined as a platelet count of < 150,000. For Physician Assistant Exam (PANCE) purposes, the primary causes of low platelets are idiopathic thrombocytopenic purpura, thrombotic thrombocytopenic purpura, and disseminated intravascular coagulation.
ITP: Platelet production problems
Idiopathic thrombocytopenic purpura (ITP) is a common cause of low platelets. Only the platelets are affected. The affected person usually has a normal WBC and Hgb/HCT.
When you think about ITP, differentiate between two types: one found in adults and one found in children. Here are the fundamental points about chronic ITP, the adult form of ITP:
Adults with ITP usually have a chronically low platelet count with a mean platelet count around 50,000.
People with chronic ITP do not have a large spleen, and petechiae may be present.
Chronic ITP is more common in women than in men; it can coexist with other connective tissue diseases or autoimmune syndromes.
The first line of treatment is prednisone. If this doesn’t work, other treatments, including intravenous immune globulin , are utilized. If other therapies don’t work, splenectomy is a last resort. Because chronic ITP is a platelet-production problem, a person with ITP can receive transfusions as needed.
ITP in children is a different animal. Here are the key points about ITP in children:
It has an abrupt onset compared to the adult condition.
ITP in children is usually caused by a viral illness. Contrast this with ITP in adults, where you should think autoimmune process.
The childhood form often gets better on its own, although in some cases prednisone may be needed.
Expect petechiae and purpura to be present, much moreso than in chronic ITP seen in adults.
Heparin-induced thrombocytopenia (HIT)
Just about everyone you see in the hospital gets heparin, either subcutaneously for DVT prophylaxis or intravenously as part of the treatment for a myocardial infarction or pulmonary embolism. Heparin is a medication that can cause the platelet count to drop. Recognize that there are actually two different types of heparin-induced thrombocytopenia.
Type I: Type I occurs 24 to 48 hours after exposure to heparin. The platelet counts will normalize, and the heparin doesn’t need to be stopped. This reaction isn’t immune mediated.
Type II: Type II can occur about 5 to 10 days after exposure to heparin. This is the biggie, mediated by the immune system, and it can be life-threatening. Even though heparin is an anticoagulant, in this situation it can cause the blood to clot! Blood clots can form in the arteries or veins. The treatment for Type II HIT is to discontinue the heparin.
Disseminated intravascular coagulation (DIC)
Disseminated intravascular coagulation is a syndrome that causes the platelets to be chewed up. Patients who have DIC are really sick — you usually find them in the intensive care unit. DIC has many causes, including sepsis, malignancy, and obstetrical complications. Here are the key points on DIC:
The lab values are vital in diagnosing DIC: low platelets, low fibrinogen levels, elevated levels of D-dimer, and a prolonged prothrombin time. The prothrombin time and its derived measures of prothrombin ratio and international normalized ratio are measures of the extrinsic pathway of coagulation.
A small percentage of the time, a hemolytic anemia can be present.
The treatment depends on what’s occurring: If there’s bleeding, you need to administer fresh frozen plasma or cryoprecipitate to replace fibrinogen. If the patient is clotting, then you may need to start heparin.
Presenting signs include bleeding from mucous membranes, digital ischemia, and gangrene.
Thrombotic thrombocytopenic purpura (TTP)
Thrombotic thrombocytopenic purpura is a systemic process where, as in disseminated intravascular coagulation, the platelets are chewed up. Common causes include medications, malignancy, and pregnancy. Here are some key points on TTP:
TTP is closely associated with a pentad: hemolytic anemia, thrombocytopenia, kidney failure, fever, and change in mental status. Note that not all five criteria need to be present; hemolytic anemia and low platelets can be enough to make the diagnosis if other laboratory parameters fit.
Key labs are an elevated LDH level and a peripheral smear that shows schistocytes. You can also see an increased bilirubin and reticulocyte level.
The gold standard of treatment is plasmapheresis. If this isn’t an option on a test question, then look for transfusion with fresh frozen plasma (FFP). It’s the next-best choice.
Which of the following medical conditions does not match its corresponding treatment?
(A) Idiopathic thrombocytopenic purpura — steroids
(B) Thrombotic thrombocytopenic purpura — fresh frozen plasma infusion
(C) Heparin-induced thrombocytopenia — protamine sulfate
(D) Disseminated intravascular coagulation — fresh frozen plasma infusion
(E) Idiopathic thrombocytopenic purpura — splenectomy
The answer is Choice (C). The treatment of HIT (Type II) is discontinuation of heparin. Protamine sulfate is used in the treatment of a heparin coagulopathy, in which the blood is too thin. All the other answers are correct.
Hemolytic uremic syndrome
Hemolytic uremic syndrome is like TTP but is usually found in children. Hemolytic uremic syndrome is rare in adults. The most common cause is Gram-negative sepsis, commonly caused by infection with E. coli 0157:H7. Other bacterial agents and viral agents can cause hemolytic uremic syndrome as well. Here are the key points:
As with TTP, you may see the pentad. However, mental status changes may be more significant in TTP, whereas kidney failure is more common in hemolytic uremic syndrome.
You don’t do plasma exchange in children with hemolytic uremic syndrome; the treatment is conservative and involves treating the underlying infection.
Sequester platelets in the spleen
Remember that your spleen sequesters about one-third of your platelets at any one time. If splenomegaly is present, more platelets can be held in the spleen. A very common cause of splenomegaly is liver disease. Liver disease can cause cirrhosis with resulting portal hypertension and splenomegaly. On a CBC, you see both a lower white cell count and thrombocytopenia because of the splenomegaly. Another cause of splenomegaly is a malignancy.