Master the board step 3

Pediatrics
Evaluate mixing studies as follows:
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If lab prolongation is corrected, there is a deficiency of clotting factor.
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If lab prolongation is not corrected or is only partially corrected, an inhibitor
is present (most common inhibitor with in-hospital patients is heparin).
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If it is more prolonged with clinical bleeding, an antibody against a clotting
factor is present (mostly factors VIII, IX, or XI).
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If there is no clinical bleeding but both the PTT and mixing study are prolonged,
lupus anticoagulant (predisposition to excessive clotting).
If the case describes
a hemophilia patient,
previously well controlled,
who presents with sudden
bleeding diathesis, order
mixing studies (coagulation
factor inhibitor—usually
factor VIII inhibitor).
Treatment
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Hemophilia A
--
Minor bleeding is treated with desmopressin (releases endogenous factor)
plus aminocaproic acid or tranexamic acid (minimize fibrinolysis).
For maximal effectiveness, antifibrinolytic medications should be given
before oral surgical procedures. Cryoprecipitate is not used.
--
Major bleeding (bleeding into joint, iliopsoas muscle, other large bleed)
is always treated by giving factor VIII.
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Hemophilia B
--
Treatment of major or minor bleeding is with factor IX concentrates
because of the thrombotic potential of prothrombin complex concentrates.
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von Willebrand’s Disease (vWD)
--
Avoid cryoprecipitate.
--
Minor bleeding and subtype 1 are treated with desmopressin (promotes
release of preformed vWF from endothelial cells).
--
Major bleeding and subtypes 2 and 3 are treated with plasma-derived
vWF-containing concentrates with factor VIII.
A 4-year-old child is brought in by her mother because of red “spots and rashes”
on her lower extremities. Today she fell from her bicycle and was bleeding for 30
minutes. She has no known medical problems, and the only significant history
is a recent upper respiratory viral illness. Examination reveals petechiae in lower
extremities and purpura on her buttocks. There are no signs of active bleeding.
PT, PTT, and bleeding time are within normal limits. Platelet count is 32,000.
Hemoglobin is 12 mg/dL. What is the next step in the workup?
a. Bone marrow biopsy
b. Factor levels
c. Mixing study
d. Peripheral smear
e. Ristocetin assay
Answer: D. This case is a classic presentation of immune thrombocytopenic purpura
(ITP) in childhood. The most common age of onset is 1–4 years, usually after a nonspecific
viral infection. The defect is autoantibodies against the platelet surfaces. Diagnosis
is by exclusion. Always get a peripheral smear to rule out TTP and HUS.
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