🧪 Station 10 — Interpretation of Coagulation Tests
🎯 Task
You are provided with the following hemostasis test results and laboratory reference ranges. Interpret each result, identify the likely type of hemostatic defect from the overall pattern, and state your conclusion.
| Test | Patient Result | Laboratory Reference |
|---|---|---|
| PT | 12.5 seconds | 11–14 seconds |
| APTT | 31 seconds | 25–35 seconds |
| Bleeding time | 12 minutes | 2–7 minutes |
| Clotting time | 7 minutes | 5–11 minutes |
⚡ Model Station Answer
What to say in the exam
- PT: Normal.
- APTT: Normal.
- Bleeding time: Prolonged, while clotting time is normal.
- Interpretation: This pattern indicates a defect of primary hemostasis, most suggestive of a platelet number or platelet-function abnormality.
- Conclusion: The screening coagulation pathways are not significantly prolonged in this result pattern.
🔎 Stepwise Procedure / Approach
- Check the laboratory reference ranges. Interpret the patient’s values against the ranges supplied in the station.
- Assess PT. A prolonged PT suggests an abnormality affecting the extrinsic or common coagulation pathway.
- Assess APTT. A prolonged APTT suggests an abnormality affecting the intrinsic or common coagulation pathway.
- Assess bleeding time. Prolongation points toward impaired primary hemostasis, particularly platelet-related or von Willebrand factor-related abnormalities.
- Assess clotting time. Marked prolongation may occur with significant coagulation-factor abnormalities; it is a relatively crude whole-blood screening test.
- Combine the results rather than interpreting one test alone. Look for an isolated or combined abnormality.
- State the hemostatic defect. Decide whether the overall pattern primarily suggests platelet/primary-hemostasis dysfunction, an intrinsic-pathway defect, an extrinsic-pathway defect, or a broader coagulation defect.
- Give one concise conclusion. State the dominant abnormality and the most likely level of hemostatic dysfunction.
| PT | APTT | Bleeding Time | Likely Pattern |
|---|---|---|---|
| ↑ | Normal | Normal | Extrinsic pathway abnormality |
| Normal | ↑ | Normal | Intrinsic pathway abnormality |
| ↑ | ↑ | Usually normal | Common pathway or multiple-factor abnormality |
| Normal | Normal | ↑ | Primary hemostasis / platelet abnormality |
🖼️ Visual Learning
Coagulation-Test Pattern Recognition
🎥 Practical Video
🎥 Practical Demonstration — Prothrombin Time (PT) & APTT
Demonstrates PT and APTT practical concepts, coagulation pathways, test procedure and examination-focused interpretation for MBBS students.
📝 Important Viva Questions
Answer: PT mainly assesses the extrinsic and common coagulation pathways.
Answer: APTT mainly assesses the intrinsic and common coagulation pathways.
Answer: It suggests an abnormality predominantly affecting the extrinsic pathway, classically involving factor VII.
Answer: It suggests an abnormality predominantly affecting the intrinsic pathway, such as deficiencies involving factors VIII, IX or XI.
Answer: It indicates impaired primary hemostasis, commonly due to a platelet-number, platelet-function or von Willebrand factor abnormality.
Answer: It suggests involvement of the common pathway or a broader multiple-factor coagulation abnormality.
Answer: Reference values vary with laboratory methods and reagents, so interpretation should be based on the range provided with the test result.