Lab Investigation of Coagulation Disorders...including Screening Tests Flashcards
What is the workup of a patient for bleeding disorders according to patient history?
Looking 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 workup of a patient for bleeding disorders according to lab testing (definitive test)?
- Manual (tilt tube) → “endpoint”
- Mechanical (Fibrometer, Start4) → “endpoint”
- Photo-optical (MLA, Coag-a-Mate, MDA II) → “endpoint”
- Chromogenic (Protein C assay) → measures proteins that don’t form a fibrin clot as an endpoint
- Immunological → Ag-Ab rxn
What type of bleeding is seen w/ a platelet and/or vascular disorder?
???
What type of bleeding is seen w/ a coagulation disorder?
???
What is the workup of a patient for bleeding disorders according to lab testing (screening tests)?
- Platelet Count
- Bleeding Time
- Prothrombin Time
- INR
- APTT
- Activated Clotting Time (ACT)
- Thrombin Clotting Time (TCT or TT)
Prothrombin Time (PT) - Principle
- Tissue thromboplastin (containing Ca2+) is added to patient plasma
- Measures the time it takes for a clot to form
Prothrombin Time (PT) - Method of activation
Addition of reagent: tissue thromboplastin + Ca2+
Prothrombin Time (PT) - Factors being measured
Extrinsic pathway: VII, X, V, II, I
Prothrombin Time (PT) - Factor deficiencies/conditions yielding abnormal/↑/prolonged results
- Deficiency of factor(s) VII, X, V, II, I
- Liver disease
- Vitamin K deficiency
- Coumadin anticoagulant therapy
- Excessive amounts of heparin
- “Circulating anticoagulants” aka “inhibitors to coagulation”
- DIC
Prothrombin Time (PT) - Reference range
10-13 seconds
Activated Partial Thromboplastin Time (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
- Ca2+ is re-added (re-calcification) and time required to clot is measured
Activated Partial Thromboplastin Time (APTT)
- Method of activation
Particulate activator (negatively-charged surface)
- Elagic acid
- Kaolin
- Silica
- Celite
Activated Partial Thromboplastin Time (APTT)
- Factors being measured
Intrinsic pathway: XII (Fletcher and Fitzgerald), XI, IX, VIII, X, V, II, I
Activated Partial Thromboplastin Time (APTT)
- Factor deficiencies/conditions yielding abnormal/↑/prolonged results
- Deficiency of factor(s)
- Liver disease
- Heparin anticoagulant therapy
- Long term Coumadin anticoagulant therapy
- “Circulating anticoagulants” aka “inhibitors to coagulation”
- DIC
Activated Partial Thromboplastin Time (APTT)
- Reference range
20-35 seconds
Activated Clotting Time (ACT)
- Principle
An activator is added to fresh whole blood and clotting time is measured (used in surgery to monitor heparin therapy)
Activated Clotting Time (ACT)
- Method of activation
Diatomaceous earth
Activated Clotting Time (ACT)
- Factors being measured
Heparin inactivated serine proteases in the intrinsic pathway: XIIa, Fletcher, XIa, IXa, Xa, Thrombin
Activated Clotting Time (ACT)
- Factor deficiencies/conditions yielding abnormal/↑/prolonged results
?
Activated Clotting Time (ACT)
- Reference range
100-125 seconds
- Minimal ACT desired during bypass is 400 seconds
International Normalized Ratio (INR)
- Definition
The ratio b/w the time it takes normal blood to clot and “Coumadin blood” to clot
- The more coumadin, the higher the INR
International Normalized Ratio (INR)
- Anticoagulant therapy that it manages
Manages coumadin anticoagulant therapy (along w/ the prothrombin time)
INR
- If on coumadin, implications of an INR < 2
At risk to form a new clot
INR
- If on coumadin, implications of an INR > 4
Bleeding risk
INR
- If not on coumadin, INR range
0.93-1.13
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
How is an INR calculated?
Patient PT result (in seconds) ÷ mean control PT value (in seconds)
