Secondary Hemostasis - Coag Cascade

Platelet plug

Not enough to stop hemorrhage in larger blood vessels

Secondary hemostasis

Activated coagulation cascade

forms insoluble, cross-linked fibrin, which help to stabilize the primary platelet plug

chatgpt explaination: 1. Endothelial cell injury
- Normally, the endothelium prevents platelet adhesion.
- When it is injured, the subendothelial matrix (collagen, vWF) is exposed.
- von Willebrand factor (vWF) is released from Weibel–Palade bodies of endothelial cells and binds exposed collagen.
- Platelets adhere to vWF through their GPIb-IX-V receptor complex, initiating platelet attachment.
- Integrins (α2β1, αIIbβ3) are also involved in binding to the matrix.
2. Platelet capture and adhesion
- Platelets are captured and tethered to the site of vascular injury.
- Adhesion occurs mainly via vWF-GPIb interaction, plus integrin receptors that anchor platelets to collagen.
- The platelets begin to spread and become activated.
3. Platelet activation
- Bound platelets undergo shape change (from discoid to spiny forms).
- Activated platelets release granules containing ADP and TxA₂ (thromboxane A₂), which further stimulate platelet activation.
- Platelets express GPVI receptor that interacts with collagen to reinforce activation.
- Activated platelets recruit additional platelets to the site of injury.
4. Platelet aggregation
- Activated platelets expose binding sites on integrin αIIbβ3 (GP IIb/IIIa).
- Fibrinogen acts as a bridging molecule, cross-linking platelets together through αIIbβ3.
- This results in the formation of a primary platelet plug.
- The plug temporarily stops bleeding (cessation of hemorrhage) but is fragile. It will later be reinforced by secondary hemostasis (fibrin formation).

Consists of the use of thromboplastin (rabbit brain) to measure the clotting time of the patient’s plasma

Correlates to Tissue factor in vivo

CaCl2 is in the Neoplastine, making it a one step reagent that is added to prewarmed plasma

Heparin inhibitor is in Neoplastine, this makes PT useful to monitor warfarin when bridging from heparin to warfarin therapy

It measures the activity of the coagulation factor II (Prothrombin), V (Proaccelerin), VII (Proconvertin), X (Stuart factor), and I (Fibrinogen)

Commonly used for monitoring vitamin K antagonist therapy

INR (International Normalized Ratio) = [(Patient’s PT)/(Mean Normal PT)]^ISI (International Sensitivity Index)

Involves the recalcification of plasma in the presence of a standardized amount of cephalin (platelet substitute) and a particulate activator (silica)

Cephalin is a phospholipid, “partial” refers to lacking tissue factor

“Activated” refers to activation of contact factor group (F12, HMWK, PK) with silica

Plasma is pre incubated several minutes before calcium is added, making this a two step reaction

Evaluates the intrinsic and common pathways; only factors VII and XIII are not evaluated

Coagulation screening test of the coagulation factors, including: Factor XII (Hageman factor), Factor XI (Plasma thromboplastin), Factor IX (Christmas factor), Factor VIII, Factor X (Stuart-Prower factor), Factor V (Proaccelarin/Labile factor), and Factor II (Prothrombin)

Heparin therapy

Calcium/Thrombin is added to diluted plasma

One step reagent

Secs are converted to mg/dL Fibrinogen

Dilution with saline buffer minimizes heparin interference

There is also a heparin inhibitor in reagent

To maintain a well-balanced state

hemorrhage might occur

hematomas may occur

Yes, monitoring is important when patient is on anticoagulation medication

Our body is constantly coagulating and anticoagulating

Excessive generation of thrombin by TF and endothelial injury combined with a lack of adequate inhibitors may contribute to a hypercoagulable state, at risk of developing microvascular thrombi

Thrombi frequently occurs in internal small vessels

Small incision is made to measure the time it took to stop bleeding

Both platelet number and function affect the bleeding time

Diseases, such as thrombocytopenia, von willebrand disease, and storage pool disorder, that affect platelet count and function would prolong bleeding time

Factors synthesized in liver

Exception is Factor 8; made in part of liver that is not affected by liver disease and also in endothelial system

Pediatric factor reference range and liver immaturity

All factors are “low” at birth except Factor 8 which is the same as adult range

Liver transplant service monitors F5 and F7

Factor 7 is a sensitive indicator because of short half life (4-6 hours)

Coagulation Factor III (also known as Tissue Factor (TF), Thromboplastin, and CD142) is the primary initiator of the extrinsic coagulation pathway

Factor VII (Stable factor)

- Factor XII (with HMW Kininogen and Prekallikrein)
- Factor XI
- Factor IX
- Factor VIII

- Factor X
- Factor V
- Factor II (Prothrombin) → Factor IIa (Thrombin)
- Factor I (Fibrinogen) → Factor Ia (Fibrin)

Severe (<1%), Moderate (1%-5%), Mild (6%-20%)

Factor VIII deficiency

Factor IX deficiency

Factor XI deficiency

No, can be congenital (X-linked) and 30% acquired without a family history

85% are boys with hemophilia A

- Factor Concentrates
- Plasma-Derived Immunopurified Products
- Recombinant Human Factor Products
- Frozen Plasma
- Cryo – Factor XIII deficiency

Factor II (Prothrombin), Factor VII, and Factor X deficiencies are rare; when they occur, they may present with spontaneous bleeding or bleeding triggered by invasive procedures

Vitamin K is a fat-soluble enzyme aids in fibrin formation

Carboxylation of y-glutamic acid GLA- residues allows these coagulation factors to bind calcium

FII, VII, IX, and X

Protein C and Protein S

Vitamin K

Answer is both, but PT is a more sensitive indicator of decreased common pathway factors

Therapeutic INR range 2.0-3.0

Therapeutic INR range is higher (2.5-3.5 or higher)

Factor 7 has the shortest half-life of 4-6 hours, Factor 2 has 60 hour half-life

The normal half-life for Factor 9 (FIX) is approximately 18-24 hours, while the half-life for Factor 10 (FX) is typically around 24-48 hours.

Warfarin affects synthesis; half life explains why it takes time for warfarin to take effect and stabilize

- Needs monitoring
- Diet restrictions (cannot eat too many leafy greens)
- Not for pregnant patients since it is a mutagenic (use LMW(Low Molecular Weight) heparin instead)
- Requires time to be effective and stabilize

Trending toward use of other oral anti-Xa like rivaroxaban and apixaban, no monitoring needed

IV Heparin drug and Affects Factor Xa and Thrombin (needs adequate AT)

Heparin is useful in emergent situation like thrombosis, since it acts
quickly (vs. warfarin)

Monitored by ACT, APTT, or Heparin test

Eventually patient needs to be bridged to an oral anticoagulant like warfarin before discharge. Bridging: patient is on heparin and warfarin until PT INR is stable

Heparin associated platelet antibody, HIT

Protamine Sulfate

- Subcutaneous drug like
Enoxaparin (Lovenox),
Nadroparin, and
Dalteparin (Fragmin)
- Affects Xa

- Monitored by Heparin test
- may be used by outpatients and used for high risk pregnancy (LA pos),

Less likely to cause HIT and no antidote available for overdose.

Rivaroxaban and Apixaban

Advantage: no monitoring needed, not affected by diet

Disadvantage: more expensive, no monitoring so compliance may be an issue. Testing may be sent out, but is not FDA approved. No antidote for overdose

Argatroban and Dabigatran

APTT Mixing study establishes the presence of an alloimmune or autoimmune factor inhibitor

Followed by Factor activity assay and Bethesda titer is performed to quantitate the inhibitor

Usually seen in intrinsic factors

Inhibitor binds to the specific factor and causes immediate clearance of the factor

Treatment requires agents that bypass factor VIII or IX such as
FEIBA FH (Factor VIII Inhibitor Bypass Activity: a plasma-derived concentrate of Factors II, VII, IX, and X that contains a combination of activated and nonactivated factors) and
recombinant activated factor VII (NovoSeven)

Enzyme produced by liver, Important endogenous anticoagulant, Inhibits the activity of most activated coagulation factors (FIIa, IXa, Xa, XIa and XIIa),

Greatest inhibitory effect is against thrombin (FIIa) and activity is enhanced by heparin, AT complexes with thrombin and the complex is then removed by the monocyte-macrophage system

Quantitative measurement of functional PC based on the prolongation of APTT

PC is activated in the presence of the Agkistrodon c. contortrix venom activator

Activated PC inhibits the factors V and VIII, and thus prolongs the APTT of a system, given that all the factors are present and constant in excess, except PC, which is derived from the sample being tested

PC deficiencies can be both acquired and congenital

Acquired PC deficiencies are found in cases of hepatic disorders.

Thrombin inhibitor

Vitamin K-dependent enzyme

Produced by liver

Antithrombotic and profibrinolytic

Protein C is activated when thrombin binds to thrombomodulin on endothelial cells

Activity of Protein C is enhanced by free Protein S, which is also vitamin K-dependent and produced in the liver

Extrinsic pathway: Tissue factor pathway inhibitor (TFPI) inhibits the TF-FVIIa complex and the TF-FVIIa-FXa complex. TFPI rapidly downregulates the initiation phase of coagulation. Activity of TFPI is promoted by Protein S. Antithrombin also weakly inhibits FVIIa.

Intrinsic Pathway: The main inhibitors are Antithrombin (AT) and Protein C.

High concentration of fibrin degradation products (FDP) can inhibit fibrin polymerization.

Inhibitors can arise in certain autoimmune diseases such as antiphospholipid antibodies in Systemic Lupus Erythematosis (SLE).

Alloantibodies – Up to 30% of severe hemophilia A and 2-3% of hemophilia B patients develop factor inhibitors after a few doses of concentrate.

- Patients >= 60 years of age may have an underlying autoimmune disorder - such as rheumatoid arthritis
- Postpartum
- Severe hemorrhage
- Sudden onset of bleeding with normal PT and abnormal PTT.

Heparin potentiates the action of antithrombin.

Unfractionated heparin has more number of pentasaccharides (than LMWH) and inhibits both FXa and thrombin.

Low Molecular Weight Heparin has shorter chain of pentasaccharides and only inhibits FXa. LMWH has more predictable pharmacodynamics and are less likely to cause excessive bleeding.

Inhibitory effect of heparin can be evaluated by prolongation of the APTT (UFH) or decreased FXa activity (UFH and LMWH).

Warfarin inhibits recycling of vitamin K, resulting in a relative deficiency of vitamin K-dependent factors (FII, VII, IX, and X) – these are being produced but they just cannot bind to PS and become activated.