Coagulation:- part 3 – Coagulation Screening Tests, and Critical values
Coagulation Screening tests
For the screening of coagulation abnormality, the following tests are advised.
- Platelets count (140,000 to 340,000 /cmm).
- Bleeding time (Ivy method <4 min and Duke method 1 to 4 min).
- Clot retraction qualitative begins in 30 to 60 minutes, completed within 24 hours but usually within 6 hours.
- Coagulation time or clotting time (5 to 15 minutes in glass tubes and 19 to 60 minutes in the siliconized tube).
- Fibrinolysins are negative.
- Prothrombin time, one stage (same as control and should be 11 to 16 seconds).
- Thromboplastin generation time (compared to normal control).
- To measure the intrinsic system, advise:
- Activated partial thromboplastin APTT.
- To measure the extrinsic system, advise:
- One stage prothrombin time PT.
The tests advised for coagulation screening workup and critical (panic) values:
|Test||Normal values||Normal values source (4)||Critical values (source 3)|
|Platelets count||150.000 to 450,000 /cmm||<100,000 (20,000 /cmm)|
|Activated partial thromboplastin time (APTT)||25 to 35 seconds||>40 seconds.|
|Prothrombin time (PT)||10 to 13 seconds||>15 seconds|
|Thrombin time (TT)||17 to 25 seconds|
|Bleeding time (BT)||2 to 8 minutes|
|Clotting time (CT)||2 to 6 minutes (glass tube 10 to 15 minutes)|
|Fibrinogen||2.0 to 4.0 g/L||<100 mg/dL|
|Fibrinogen degradation products (FDP)||< 10 mg/L||
|Plasma D-dimer||< 200 mg/L||<250 µg/L|
|Coagulation factors||500 to 1500 U/L|
|Factor VIII||<100% and >160%|
|Protein C||70 to 1400 U/L|
|Protein S total||70 to 1400 U/L|
Critical values of blood coagulation screening test:
- Platelets = <50,000/cmm or > 1 million/cmm.
- APTT = >70 seconds.
- PTT = >100 seconds.
- Fibrinogen = <100 mg/dL.
Differential diagnoses of bleeding disorders:
|APTT||PT||Platelets count||Causes of bleeding disorders|
Questions and answers:
Question 1: What is the critical value of fibrinogen?
Fibrinogen critical value is <100 mg/dL.
Question 2: What is the critical value of APTT?
APTT critical value is >70 seconds.