Approach to Bleeding Disorders in Children
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Direct answer
Bleeding disorders in children are defects of haemostasis, and the initial approach reads prothrombin time, activated partial thromboplastin time, platelet count and bleeding time to localise the defect. A prolonged aPTT with normal PT points to an intrinsic pathway defect, as in haemophilia. A normal platelet count with prolonged bleeding time suggests a platelet function disorder or von Willebrand disease.
What you must remember
- Primary haemostasis: platelet plug formation, and defects cause mucocutaneous bleeding such as petechiae, epistaxis and gum bleeding.
- Secondary haemostasis: coagulation factors, and defects cause deep bleeding into joints and muscles, as in haemophilia.
- Prothrombin time: tests the extrinsic and common pathways, and factor VII falls first in early vitamin K deficiency.
- aPTT: tests the intrinsic and common pathways, and heparin prolongs it.
- Platelet count: a low count causes petechiae and bruising, and immune thrombocytopenia is the commonest acquired cause of isolated thrombocytopenia in children.
- Mixing study: correction of a prolonged clotting time suggests factor deficiency, while failure to correct suggests an inhibitor.
- Specific assays: factor VIII and IX levels, von Willebrand factor antigen and activity, and platelet aggregation studies confirm the defect.
Matching the laboratory pattern to the likely defect
Bleeding history and the pattern of laboratory results usually localise the defect within minutes. The table pairs each pattern with its likely cause and typical examples.
| Laboratory pattern | Likely defect | Examples |
|---|---|---|
| Prolonged aPTT, normal PT and platelets | Intrinsic pathway factor | Haemophilia A and B |
| Prolonged PT, normal aPTT | Extrinsic pathway factor | Factor VII deficiency, early vitamin K deficiency |
| Prolonged PT and aPTT, platelets usually normal | Common pathway or multiple factors | Liver disease, severe vitamin K deficiency (DIC also lowers platelets) |
| Low platelets, normal coagulation | Thrombocytopenia | Immune thrombocytopenia, marrow failure |
| Normal counts, prolonged bleeding time | Platelet function or von Willebrand | Glanzmann thrombasthenia, von Willebrand disease |
| Prolonged aPTT, no correction on mixing | Inhibitor | Factor VIII inhibitor in haemophilia |
Pattern recognition beats memorising each disease, because the table narrows the differential, and the mixing study and bleeding phenotype help when two patterns overlap. Confirm the chosen diagnosis with factor assays, a von Willebrand panel or platelet function studies, and repeat testing when results are borderline.
Where the exam tries to catch you
Bleeding disorder vignettes often tempt students to stop at the first abnormal test, and the traps below show where that goes wrong.
- Trap: reading a prolonged aPTT as proof of haemophilia. Correct: heparin, a lupus anticoagulant and factor deficiencies all prolong aPTT, so a mixing study and factor assay are needed.
- Trap: calling a normal platelet count reassuring in a child with easy bruising. Correct: platelet function disorders and von Willebrand disease give normal counts, so bleeding time and specific tests are needed.
- Trap: assuming vitamin K deficiency always prolongs both PT and aPTT. Correct: early deficiency lowers factor VII first, so the PT rises before the aPTT, and severe deficiency prolongs both.
Frequently asked questions
Which tests are done first for suspected bleeding disorder in a child?
The prothrombin time, activated partial thromboplastin time and full blood count are the first tests for a child with suspected bleeding disorder. Together they separate defects of the extrinsic, intrinsic and common pathways from defects of platelet number.
Why is aPTT prolonged in haemophilia?
The aPTT is prolonged in haemophilia because factor VIII or factor IX deficiency impairs the intrinsic pathway. The prothrombin time is usually normal because the extrinsic pathway is intact.
What is a mixing study used for?
A mixing study combines the child's plasma with normal plasma to test whether a prolonged clotting time corrects. Correction suggests a factor deficiency, whereas failure to correct suggests an inhibitor such as a factor VIII antibody.
Which tests assess platelet function in children?
Platelet function is assessed by platelet aggregation studies and a platelet function analyser, with bleeding time used in some centres. Abnormal results point to disorders such as Glanzmann thrombasthenia or von Willebrand disease.
How is von Willebrand disease diagnosed?
Von Willebrand disease is diagnosed by measuring von Willebrand factor antigen and activity, together with factor VIII levels. Results are interpreted with the bleeding history, because levels can vary with age, blood group and stress.