Screening Tests Flashcards
What is the work-up of a patient for bleeding disorder according to patient history
Look for past bleeding episodes, past surgeries, family history, drug history
- Has the bleeding been out of proportion to the challenge/injury
What is the work-up of a patient for bleeding disorder according to physical examination
Does type of bleed point to a disorder? (primary, secondary, both?)
What is the work-up of a patient for bleeding disorder according to lab testing
- Manual
- Mechanical
- Photo-optical
- Chromogenic
- Immunological
Screening tests v.s definitive test
Screening:
- Platelet Count
- Bleeding Time
- Prothrombin Time
- INR
- APTT
- Activated Clotting Time (ACT)
- Thrombin Clotting Time (TCT or TT)
PT:
- principle
Tissue thromboplastin (containing calcium) is added to patient plasma; time required for a clot to form is measured
PT:
- method of activation
Addition of the reagent - tissue thromboplastin + calcium
PT:
- factors being measured
Extrinsic Pathway: VII, X, V, II, I
PT:
- factor deficiencies/conditions yielding abnormal results
- Deficiency of factor(s)
- Liver disease
- Vit K deficiency
- Coumadin anticoagulant therapy
- Excessive amounts of heparin
- “circulating anticoagulants” aka “inhibitors to coagulation”
- DIC
PT:
- Reference range
10-13 seconds
APTT:
- principle
A phospholipid substitute for platelets (“partial thromboplastin”) along with a negatively charged particulate activator is added to patient plasma to activate contact factors
- Calcium is re-added and time required to clot is measured
APTT:
- method of activation
Particulate activator (neg charged surface)
APTT:
- factors being measured
Intrinsic Pathway:
XII (Fletcher and Fitzgerald), XI, IX, VIII, X, V, II, I
APTT:
- factor deficiencies/conditions yielding abnormal results
- Deficiency of factor(s)
- Liver disease
- Heparin anticoagulant therapy
- Long term Coumadin anticoagulant therapy
- “circulating anticoagulants” aka “inhibitors to coagulation”
- DIC
APTT:
- Reference range
20-35 seconds
ACT:
- principle
An activator added to fresh whole blood and clotting time is measured (used in surgery to monitor heparin therapy)
ACT:
- method of activation
Diatomaceous earth
ACT:
- factors being measured
Heparin inactivated serine proteases in the intrinsic pathway:
XIIa, Fletcher, XIa, IXa, Xa, Thrombin
ACT:
- factor deficiencies/conditions yielding abnormal results
?
INR:
- definition
ratio between the time it takes normal blood to clot and “Coumadin blood” to clot
INR:
- anticoagulant therapy that it manages
Manages coumadin anticoagulant therapy (along with the prothrombin time)
INR:
- implications of an INR less than two
at risk to from new clot
INR:
- implication of an INR over 4
bleeding risk
Thrombin Clotting Time:
- principle
The reagent thrombin is added to plasma and the time required for clot formation is measured
Thrombin Clotting Time:
- conditions yielding prolonged results
- Afribrinogenemia, Hypofibrinogenemia, Dysfibrinogenemia
- “Antithrombins” (Heprin and FDPs)
- “circulating anticoagulants”
- DIC
- Thrombin inhibitors (Pradaxa)
- NOT COUMADIN
Thrombin Clotting Time:
- purpose of substituting reptiles for thrombin (Reptilase time)
It is capable of converting fibrinogen to fibrin (like thrombin) but it is unaffected by heparin. So it is helpful in testing for functional fibrinogen when the TCT is prolonged due to heparin.
