Authentic and Spurious Causes of Thrombocytopenia Exam

Which one of the following is the mechanism for the production of platelet satellitism?

An IgG antibody is directed against GP IIb/IIIA on the platelet membrane Feedback Platelet satellitism is a rare situation in which an IgG antibody is directed against the glycoprotein IIb/IIIa complex on the platelet membrane. The antibody-coated platelets rosette around neutrophils, causing a falsely low platelet count to be recorded with automated instrumentation. Monocytes may also show some rosetting. No antibodies are formed against Factor VIII, vWF, or fibrinogen that result in platelet satellitism.

What is the mechanism of heparin-induced thrombocytopenia (HIT)?

Antibodies directed against platelet factor 4 (PF-4) and heparin complex Feedback HIT is a complication that may occur in some patients receiving heparin therapy. When heparin is administered to these patients, it forms an immune complex with platelet factor 4 (PF-4) that is released from the alpha granules in platelets. The body's immune system recognizes this complex as a foreign substance and forms an antibody against it. The antibody binds to this complex and the platelets are destroyed. HIT is not the result of administration of toxic doses of heparin. The dosing is correct; the thrombocytopenia is the result of the patient's immune response to the heparin. Abrupt cessation of heparin therapy will not cause thrombocytopenia. If a patient is diagnosed with HIT, heparin therapy should be stopped immediately and replaced with a different anticoagulant therapy if necessary.

Acute idiopathic thrombocytopenic purpura (ITP) is MOST OFTEN associated with which of these populations?

Children 1 - 7 years of age Feedback Acute ITP occurs most often in children who are between 1 and 7 years of age subsequent to a viral infection such as measles, rubella, Epstein Barr, chicken pox or cytomegalovirus (CMV). The platelet count drops precipitously to between 20 - 50 x 109/L and the child may experience excessive bruising, nose bleeds, or petechiae. Rarely, a form of ITP may occur in newborn infants of mothers with ITP. Chronic ITP occurs most often in adults who are 20 - 40 years of age. It is also more common in females than males.

A woman in labor is bleeding, has a very high fever, and is in danger of losing the fetus. Laboratory results include a platelet count of 15 x 109/L (normal platelet count = 150 - 450 x 109/L), prolonged PT and aPTT, decreased fibrinogen, and increased D-dimer. Her automated blood count flagged for blood smear review, and the cells indicated by the arrows were seen on her peripheral smear along with a decrease in the number of platelets present. What condition is suggested by these results?

Disseminated intravascular coagulation (DIC) Feedback As we can see from this patient's laboratory test results, her D-dimer is elevated, her PT and aPTT are prolonged, her fibrinogen and platelet count are dramatically decreased. This is a classic profile for DIC. Thrombocytopenia and the presence of schistocytes on the peripheral blood smear are also associated with TTP and HUS, but the abnormal D-dimer and coagulation tests point to DIC.

Which of the following processes can lead to the formation of microclots in a patient specimen that is collected in a tube containing EDTA anticoagulant?

Failing to invert the tube after specimen collection. Feedback Failing to invert a tube containing an anticoagulant such as EDTA can cause the formation of microclots. This can result in a falsely-decreased platelet count. The other choices that are listed are all acceptable practices and will not cause the formation of microclots in an EDTA tube.

Which of the following causes schistocyte formation in disseminated intravascular coagulation (DIC)?

Microthrombi disposition in small vessels Feedback Schistocytes are the result of erythrocytic membrane damage caused by sheering of red blood cells as they pass through a fibrin mesh of clot formation occurring in the blood vessels. This occurs in DIC, TTP and HUS. Therefore, schistocytes may be seen in all three of these conditions.

Which laboratory result is the most critical in recognizing heparin-induced thrombocytopenia (HIT)?

Platelet count Feedback Patients receiving heparin therapy should have periodic platelet counts to detect possible HIT. Anaylzing a patient's sample for aPTT, PT, and D-dimer are not helpful in detecting HIT.

What is a corrective action that can be used to obtain a valid platelet count from a patient specimen that exhibits platelet satellitism on the manual differential?

Recollect the blood specimen in a blue top tube containing sodium citrate. Feedback If either platelet satellitism or platelet clumps are observed on the peripheral smear, the sample should be recollected using sodium citrate as the anticoagulant. Platelets can then be counted using the automated method. The platelet count from a tube that contains liquid sodium citrate will need to be corrected for the dilutional effect of the citrate; this can be accomplished by multiplying the platelet count that is obtained from the automated analyzer by 1.1. Any suggested remedy that involves the use of EDTA as the anticoagulant will not be effective because the presence of EDTA is causing the satellitism to occur.

Removal of which of these organs may be a last resort treatment for a patient whose platelet count is less than 30 x 109/L as a result of chronic idiopathic thrombocytopenic purpura (ITP)?

Spleen Feedback In ITP, antibodies develop that coat the platelets. The spleen produces macrophages whose Fc receptors recognize and destroy these antibody-coated platelets. Removing the spleen would decrease platelet destruction, but it is a last resort since the immunologic function of the spleen would also be lost. Removing the gall bladder, pancreas, or a kidney would not improve thrombocytopenia caused by ITP.

Plasma exchange is the current treatment for which of these conditions?

Thrombotic thrombocytopenic purpura (TTP) Feedback Currently, the most effective treatment for TTP is plasma exchange. The patient's plasma is replaced with donor plasma over a period of several days until the patient's entire plasma volume has been exchanged.