Activated partial thromboplastin time (APTT) is prolonged in?

AIIMS Bhuvneshwar NO- 2018

Pathology & Genetics

Easy

Appeared in: AIIMS Bhuvneshwar NO- 2018

Explanation

The Activated Partial Thromboplastin Time (APTT) test measures the integrity of the intrinsic and common pathways of the coagulation cascade.
The intrinsic pathway includes clotting factors VIII and IX.
Hemophilia is a genetic disorder defined by a deficiency of either Factor VIII (Hemophilia A) or Factor IX (Hemophilia B).
This deficiency impairs the intrinsic pathway, leading to a delayed clot formation and therefore a prolonged APTT value.
A normal APTT is about 25-35 seconds; in hemophilia, this time is significantly longer.

Option A: Bone marrow depression affects the production of blood cells (platelets, RBCs, WBCs). It does not affect the synthesis of coagulation factors, which are proteins produced by the liver. Therefore, APTT remains normal.
Option C: Thrombocytopenia is a low platelet count. Platelets are involved in primary hemostasis (plug formation), which is measured by bleeding time. APTT measures the secondary hemostasis factor cascade and is not affected by platelet count alone.
Option D: Thrombosis is the pathological formation of a blood clot within a vessel. It is a state of hypercoagulability, the opposite of a bleeding disorder that would prolong clotting time. Conditions causing thrombosis do not prolong APTT.

Visual 1: Diagram: The coagulation cascade, highlighting the intrinsic, extrinsic, and common pathways. This visual helps differentiate the factors measured by APTT versus PT.
Visual 2: Table: A comparative chart of common coagulation tests (APTT, PT/INR, Thrombin Time, Bleeding Time), detailing what each test measures, normal values, and common causes for abnormal results.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Interpretation of Activated Partial Thromboplastin Time (APTT) in coagulation disorders as background academic context rather than a clinical decision trigger.
Nurses are responsible for monitoring APTT levels, especially in patients receiving intravenous heparin therapy. The therapeutic goal for heparin is typically an APTT of 1.5 to 2.5 times the normal control value.
A critically high APTT value indicates a high risk of spontaneous bleeding. The nurse must promptly report this to the physician, stop the heparin infusion if applicable, and monitor the patient for signs of hemorrhage (e.g., bruising, hematuria, melena).
What if? If a patient had a prolonged Prothrombin Time (PT) but a normal APTT, the nurse should suspect a problem with the extrinsic pathway (e.g., Factor VII deficiency) or the effects of warfarin, not hemophilia.

How to Approach the Question

First, identify the key term in the question: 'Activated partial thromboplastin time (APTT) is prolonged'.
Recall the purpose of the APTT test. It assesses the function of the intrinsic and common pathways of blood coagulation.
Think about the factors included in the intrinsic pathway: Factors XII, XI, IX, and VIII.
Evaluate each option based on its pathophysiology:
A) Bone marrow depression: Affects blood cells, not clotting factors from the liver.
B) Hemophilia: A classic disorder involving deficiency of intrinsic pathway factors (VIII or IX).

Concept Tested & Keywords

Concept Tested: Interpretation of Activated Partial Thromboplastin Time (APTT) in coagulation disorders.
Stem keywords: Activated partial thromboplastin time, APTT, prolonged
Lead-in keywords: BEST, MOST RELEVANT CLUE
Negative lead-in flag: false

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