Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
I now have comprehensive information from multiple authoritative textbooks. Here is the complete answer covering all 5 objectives from the lab sheet:
Bleeding Time (BT) - Duke's Method: Complete Lab Guide
Objective 1 - Definition of Bleeding Time
Bleeding time (BT) is the time interval from the moment a standardized skin wound is made to the moment bleeding spontaneously stops. It is a measure of primary hemostasis - specifically testing the ability of platelets to form a temporary plug at the site of vascular injury (platelet adhesion, activation, and aggregation, plus vasoconstriction).
- Guyton and Hall Textbook of Medical Physiology
- Henry's Clinical Diagnosis and Management by Laboratory Methods
Objective 2 - Determining BT by Duke's Method
Duke's Method (the classic/original technique, still taught in physiology practicals):
| Step | Detail |
|---|---|
| Site | Tip (pulp) of the ring finger or earlobe |
| Wound | A small puncture/incision made with a sterile lancet |
| Technique | Every 30 seconds, gently blot the blood drop with filter paper (without touching the wound itself) |
| End point | When blood no longer stains the filter paper = bleeding has stopped |
| Timer | Start immediately when the puncture is made; stop when bleeding ceases |
The requirement listed in the image (Lancet) is precisely the instrument used in Duke's method.
Objective 3 - Normal Value of BT
Normal BT by Duke's method: 1-6 minutes (most sources state 2-5 minutes as a tighter reference range)
"When a sharp-pointed knife is used to pierce the tip of the finger, bleeding ordinarily lasts for 1 to 6 minutes."
- Guyton and Hall Textbook of Medical Physiology
Values >9 minutes are generally considered abnormal. Bleeding time >15 minutes predicts significant surgical bleeding.
- Morgan and Mikhail's Clinical Anesthesiology, 7e
Objective 4 - Other Methods of Estimating BT
| Method | Technique | Notes |
|---|---|---|
| Duke's method | Finger-tip/earlobe lancet puncture | Classic; variable due to lack of standardization |
| Ivy's method | Standardized incision on volar forearm; BP cuff at 40 mmHg | More reproducible; 3 small incisions |
| Template (Mielke) method | Template device ensuring uniform 1 cm × 1 mm incision on forearm; BP cuff at 40 mmHg | Most standardized; still suffers variability |
| PFA-100/PFA-200 (Platelet Function Analyzer) | Blood flows under high shear through a collagen/ADP or collagen/epinephrine membrane; closure time measured | Modern replacement for BT in most hospitals |
| Cone and Plate (Impact-R) | Uses shear forces to assess platelet function | Research/specialized use |
The template bleeding time (Ivy + template) was the gold standard for decades but has been largely abandoned due to poor predictive value, risk of scarring, and significant technical variability. The PFA-100 is the current modern alternative.
- Henry's Clinical Diagnosis and Management by Laboratory Methods
- Tietz Textbook of Laboratory Medicine, 7th Edition
Objective 5 - Conditions in Which BT is Increased (Prolonged)
BT is prolonged in conditions affecting platelet number, platelet function, or blood vessel integrity:
A. Platelet Disorders
| Category | Examples |
|---|---|
| Thrombocytopenia (low platelet count) | ITP, aplastic anemia, bone marrow suppression, hypersplenism, DIC, Fanconi anemia, Wiskott-Aldrich syndrome |
| Qualitative platelet defects (normal count but abnormal function) | Glanzmann's thrombasthenia (absent GP IIb/IIIa), Bernard-Soulier disease (absent GP Ib/V/IX), storage pool disorders (Hermansky-Pudlak, gray platelet syndrome) |
B. Drug-Induced
| Drug | Mechanism |
|---|---|
| Aspirin | Irreversibly inhibits cyclooxygenase → impairs TXA2 production; lasts up to 8 days (platelet lifespan) |
| Other NSAIDs (ibuprofen, etc.) | Reversibly inhibit COX; lasts ~24 hours |
| Clopidogrel, ticagrelor | ADP receptor blockers; impair platelet function for platelet lifespan |
C. von Willebrand Disease (vWD)
- Most common inherited bleeding disorder (1:800-1,000 people)
- Deficient or defective vWF impairs platelet adhesion to subendothelium
- Presents with prolonged BT + low vWF antigen + decreased Factor VIII activity
- Morgan and Mikhail's Clinical Anesthesiology, 7e
D. Vascular Disorders
- Hereditary hemorrhagic telangiectasia
- Scurvy (vitamin C deficiency - capillary fragility)
- Ehlers-Danlos syndrome
E. Systemic Conditions
| Condition | Mechanism |
|---|---|
| Chronic Kidney Disease (uremia) | Uremic toxins impair platelet factor III activity and aggregation |
| Liver disease / cirrhosis | Reduced thrombopoietin production → thrombocytopenia |
| DIC | Platelet consumption |
| Viral hemorrhagic fevers | Platelet destruction + dysfunction |
Summary Table
| Parameter | Details |
|---|---|
| Test measures | Primary hemostasis (platelet plug formation) |
| Method | Duke's: lancet to fingertip/earlobe |
| Normal range | 1-6 minutes |
| Prolonged by | Thrombocytopenia, platelet dysfunction, vWD, aspirin/NSAIDs, uremia |
| Modern replacement | PFA-100/PFA-200 |
Note: Bleeding time does NOT test the coagulation cascade (clotting factors). A prolonged BT with a normal platelet count points to a qualitative platelet defect or vWD rather than a coagulation factor deficiency. Hemophilia A and B, for example, have normal BT.
This is a shared conversation. Sign in to Orris to start your own chat.