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Human Physiology · Blood and immunity

Haemostasis and Coagulation

Haemostasis stops bleeding without blocking healthy vessels. When the balance tips, patients bleed or form clots. This page explains how vessels, platelets and clotting proteins work together, how anticoagulant drugs act, and what the evidence says about preventing and recognising deep vein thrombosis.

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10Questions

Part 6 · Blood and Immunity · Chapter 28 of 47

Learning objectives

By the end of this page you should be able to:

  • Describe the four steps of haemostasis.
  • Outline the coagulation cascade and the action of common anticoagulants.
  • Explain the natural controls that stop clots spreading.
  • Apply Virchow’s triad to hospital patients.
  • Describe the evidence for mechanical prevention of DVT after stroke.
  • Recognise suspected DVT and understand how it is ruled out.

Why it matters

Venous thromboembolism is a common, preventable cause of death in hospital. Physiotherapists mobilise patients after surgery and stroke, often see the first signs of a clot, and apply compression devices.

Many patients also take anticoagulants or antiplatelet drugs, which affect bruising, bleeding after falls and the safety of some manual techniques.

The steps of haemostasis

Figure 1 · The four steps of haemostasis

Vascular spasm, platelet plug, coagulation and fibrinolysis Four boxes in sequence: vessel spasm in seconds, platelet plug in minutes, coagulation forming a fibrin mesh in minutes, and fibrinolysis dissolving the clot over days. 1. Vessel spasmsmooth muscle narrowsthe injured vesselseconds2. Platelet plugplatelets stick to exposedcollagen and to each otherminutes3. Coagulationfibrin mesh stabilisesthe plug into a clotminutes4. Fibrinolysisplasmin dissolves the clotas the vessel healsdaysToo little clotting: bleeding. Too much: thrombosis.Haemostasis balances the two.
Stop the bleeding, then clear the clot. Each step can fail or overshoot, which is why bleeding disorders and thrombosis both occur.
StepKey playersWhat goes wrong
Vessel spasmSmooth muscle, endothelinRarely the main problem
Platelet plugPlatelets, von Willebrand factor, collagenLow platelets, antiplatelet drugs: bruising, nosebleeds
CoagulationClotting factors, calcium, vitamin KHaemophilia, liver disease, anticoagulants: deep bleeding
FibrinolysisPlasminogen, plasminToo little: clots persist; too much: bleeding

The coagulation cascade

Figure 2 · The coagulation cascade, simplified

Simplified coagulation pathway with sites of anticoagulant drugs Tissue factor from injury starts the pathway; the contact pathway amplifies it. Both activate factor X, which converts prothrombin to thrombin. Thrombin converts fibrinogen to fibrin and amplifies its own production. Side notes show where warfarin, direct oral anticoagulants and heparins act. Tissue factor pathwayinjury exposes tissue factor (VII)Contact pathwayamplifies (XII, XI, IX, VIII)Factor X activatedProthrombin → thrombinFibrinogen → fibrin clotthrombin amplifiesits own productionWarfarinblocks vitamin K-dependentfactors II, VII, IX, XDOACsblock factor Xa orthrombin directlyHeparinsboost antithrombin(Xa and thrombin)
Thrombin is the key enzyme. Many of your patients take drugs that act on this pathway, which raises bleeding risk after falls or injections.

Injury exposes tissue factor, which starts a chain of enzyme reactions. Each step amplifies the last, so a small trigger produces a large burst of thrombin. Thrombin turns soluble fibrinogen into fibrin strands that bind the platelet plug into a firm clot.

Most clotting factors are made in the liver, and several need vitamin K. Calcium is required at many steps.

Natural brakes

Healthy endothelium releases nitric oxide and prostacyclin that keep platelets inactive. Antithrombin, protein C and protein S switch clotting off, and plasmin dissolves fibrin. Inherited defects in these brakes raise the risk of thrombosis.

Drug groupExamplesActionPhysiotherapy note
AntiplateletAspirin, clopidogrelStop platelets stickingMore bruising; care with deep soft tissue work
Vitamin K antagonistWarfarinFewer functional clotting factorsBleeding risk varies with INR
Direct oral anticoagulantsApixaban, rivaroxaban, dabigatranBlock factor Xa or thrombinBleeding risk after falls; head injury needs urgent review
HeparinsEnoxaparinBoost antithrombinInjection-site bruising

Venous thrombosis

Figure 3 · Why clots form in veins

Virchow’s triad of stasis, vessel wall injury and hypercoagulability A triangle with venous thrombosis at the centre and three corners: stasis of blood from immobility, vessel wall injury from surgery or trauma, and hypercoagulability from cancer, pregnancy, oestrogen or inherited disorders. A note shows that physiotherapy targets stasis. VenousthrombosisStasis of bloodimmobility, bed rest, paralysis,long travel, plaster castsVessel wall injurysurgery, trauma, fracturesHypercoagulabilitycancer, pregnancy, oestrogen, inheritedPhysiotherapy targetsstasis: early mobilisation,calf pumps, mechanicalcompression [3]
Most hospital patients have at least two corners. Movement is the corner we can change.

Clots in leg veins form where blood is slow, the vessel wall is damaged, or the blood is more prone to clot. Surgery, fractures, stroke, cancer and immobility commonly combine these factors. A clot can break off and lodge in the lungs as a pulmonary embolus.

Red flags

New calf pain, swelling, warmth and redness, especially after surgery or immobility, suggest DVT. Sudden breathlessness, chest pain or coughing blood suggest pulmonary embolism. Stop treatment and seek urgent medical assessment.

Recognising and ruling out DVT

D-dimer is a breakdown product of fibrin. It is raised when clots form and dissolve, but also after surgery, infection and in older age, so it is better at ruling out than ruling in. Wells and colleagues showed that a low clinical probability plus a negative D-dimer safely excludes DVT [1].

Figure 4 · Ruling out a clot

Diagnostic pathway combining clinical probability and D-dimer for suspected deep vein thrombosis A flow chart. Suspected DVT is scored for clinical probability. If clinically unlikely, D-dimer is checked: a negative result rules out DVT without a scan, and a positive one leads to ultrasound. If clinically likely, ultrasound follows directly. Suspected DVTclinical probability scoreClinically unlikelycheck D-dimerClinically likelyultrasoundD-dimer negativeDVT ruled out;no scan neededD-dimer positiveultrasound39% avoided ultrasound;missed clots 0.4% at 3 months [1]
A low score plus a negative D-dimer is reassuring. Thirty-nine per cent of patients avoided ultrasound safely [1].

Preventing DVT after stroke

Immobile stroke patients are at high risk. Two large trials tested mechanical methods. In CLOTS 1, thigh-length stockings did not reduce proximal DVT and caused more skin breaks and ulcers [2]. In CLOTS 3, intermittent pneumatic compression reduced proximal DVT from 12.1% to 8.5% [3].

Figure 5 · Mechanical prevention after stroke

Proximal deep vein thrombosis with stockings or intermittent compression after stroke Paired bars. With thigh-length stockings, proximal clots occurred in 10.0 per cent versus 10.5 per cent without. With intermittent pneumatic compression, they occurred in 8.5 per cent versus 12.1 per cent without. 10.5%Control10.0%DeviceThigh-length stockings (CLOTS 1)12.1%Control8.5%DeviceIntermittent pneumatic compression (CLOTS 3)no meaningful benefit [2]absolute reduction 3.6% [3]
Not all compression works. Stockings did not reduce clots and caused more skin damage [2]; pneumatic compression did reduce clots in immobile stroke patients [3].

Skin breaks were more frequent with pneumatic compression too, so skin checks matter [3]. Early mobilisation, hydration and medication, where appropriate, complete prevention.

Practical skill · using pneumatic compression safely

Check skin and circulation before applying sleeves and daily thereafter [3]. Do not apply to a leg with suspected existing DVT, severe arterial disease or broken skin. Remove for mobilisation, and replace afterwards if the patient remains largely immobile.

Clinical relevance for the physiotherapist

  • Prevention. Early mobilisation and active calf exercises reduce stasis.
  • Stroke units. Use pneumatic compression, not thigh-length stockings, for immobile patients [2, 3].
  • Suspected DVT. Stop, do not massage or mobilise vigorously, and refer for assessment [1].
  • Anticoagulated patients. Watch for bruising and bleeding; any head injury after a fall needs urgent review.
  • Low platelets. Avoid high-impact and deep manual techniques; follow local thresholds.

Assessment and application

SituationInterpretationAction
Day 3 after hip fracture repair, swollen warm calfPossible DVTStop; medical assessment; D-dimer and ultrasound pathway [1]
Immobile stroke patient, no contraindicationsHigh DVT riskPneumatic compression [3]; avoid relying on stockings [2]
Patient on apixaban falls and hits headBleeding riskUrgent medical review even if well
Platelets very low during chemotherapyBleeding riskGentle activity; avoid falls and deep pressure

Common mistakes

  • Applying graduated stockings as routine stroke DVT prevention [2].
  • Massaging a swollen calf before DVT is excluded.
  • Assuming a raised D-dimer proves DVT [1].
  • Forgetting to check skin under compression devices [3].
  • Ignoring anticoagulant use when assessing a fall.

Exam preparation

Long answer

Describe the mechanism of blood coagulation. Add a note on anticoagulants.

  • Steps of haemostasis (Figure 1).
  • Coagulation cascade and thrombin (Figure 2).
  • Natural anticoagulants and fibrinolysis.
  • Anticoagulant drugs (table).
  • Clinical: DVT, Virchow’s triad and prevention [2, 3].

Short notes

  • Platelets.
  • Vitamin K and clotting.
  • D-dimer [1].
  • Mechanical DVT prophylaxis [2, 3].

Viva and practical

  • “Name Virchow’s triad.” — stasis, vessel injury, hypercoagulability.
  • “Do stockings prevent DVT after stroke?” — thigh-length stockings did not [2].
  • “What did CLOTS 3 show?” — pneumatic compression reduced DVT [3].
  • OSCE: screen a post-operative patient for DVT before mobilising.

Current evidence

Exam and traditional teaching

Graduated compression stockings are standard DVT prevention for all immobile patients.

What the evidence adds

After stroke, thigh-length stockings did not reduce DVT and harmed skin [2]; pneumatic compression did reduce DVT [3].

Clinical probability plus D-dimer can safely exclude DVT [1].

What the student should understand

Movement fights stasis, the right device helps when movement is impossible, and a suspicious calf always needs assessment first.

Check yourself

10 questions on this page. Tap one to see the answer and the reasoning.

Q1. In the Wells D-dimer trial, DVT could be safely ruled out without ultrasound when:
  1. (A) The patient was young
  2. (B) Clinical probability was unlikely and D-dimer was negative
  3. (C) D-dimer was positive
  4. (D) The leg was painful

Answer: (B) An unlikely clinical score plus negative D-dimer ruled out DVT [1].

Q2. What proportion of patients in the D-dimer group avoided ultrasound?
  1. (A) About 5%
  2. (B) About 39%
  3. (C) About 90%
  4. (D) None

Answer: (B) Two hundred eighteen patients (39%) did not need ultrasound [1].

Q3. In CLOTS 1, thigh-length graduated compression stockings after stroke:
  1. (A) Halved DVT
  2. (B) Did not significantly reduce DVT and increased skin damage
  3. (C) Increased DVT
  4. (D) Were not tested

Answer: (B) DVT was 10.0% vs 10.5%; skin problems were more common with stockings [2].

Q4. Skin breaks, ulcers or necrosis with stockings in CLOTS 1 occurred in:
  1. (A) 1% vs 5%
  2. (B) 5% vs 1%
  3. (C) 50% vs 10%
  4. (D) 0%

Answer: (B) Skin complications occurred in 5% with stockings versus 1% without [2].

Q5. In CLOTS 3, intermittent pneumatic compression in immobile stroke patients reduced proximal DVT from:
  1. (A) 12.1% to 8.5%
  2. (B) 8.5% to 12.1%
  3. (C) 50% to 10%
  4. (D) No change

Answer: (A) Proximal DVT fell from 12.1% to 8.5%, an absolute reduction of 3.6% [3].

Q6. Which patients were enrolled in CLOTS 3?
  1. (A) Athletes
  2. (B) Immobile patients with acute stroke
  3. (C) Outpatients with knee pain
  4. (D) Children

Answer: (B) Patients who could not walk to the toilet unaided after acute stroke [3].

Q7. Which side effect was more common with pneumatic compression in CLOTS 3?
  1. (A) Falls with injury
  2. (B) Skin breaks on the legs
  3. (C) Bleeding
  4. (D) Stroke extension

Answer: (B) Skin breaks occurred in 3% vs 1% [3].

Q8. The step of Virchow’s triad that physiotherapists most directly influence is:
  1. (A) Inherited clotting disorders
  2. (B) Stasis of blood
  3. (C) Cancer
  4. (D) Oestrogen use

Answer: (B) Movement and mechanical compression address stasis; compression reduced DVT after stroke [3].

Q9. Overall prevalence of DVT or pulmonary embolism among outpatients with suspected DVT in the Wells trial was about:
  1. (A) 1.5%
  2. (B) 15.7%
  3. (C) 57%
  4. (D) 90%

Answer: (B) Prevalence was 15.7% [1].

Q10. A practical lesson from CLOTS 1 is that:
  1. (A) Stockings should be used routinely in acute stroke
  2. (B) Thigh-length stockings should not be relied on to prevent DVT after stroke
  3. (C) Stockings prevent all clots
  4. (D) Stockings have no side effects

Answer: (B) The results did not support thigh-length stockings in acute stroke [2].

Quick review

Key takeaways

  • Haemostasis: spasm, platelet plug, coagulation, fibrinolysis.
  • Thrombin converts fibrinogen to fibrin and amplifies itself.
  • Anticoagulants act on vitamin K factors, factor Xa or thrombin.
  • Virchow: stasis, vessel injury, hypercoagulability.
  • Unlikely score + negative D-dimer rules out DVT [1].
  • After stroke: stockings no benefit [2]; pneumatic compression reduces DVT [3].

Further reading

SourceWhy it earns its place
Wells PS et al. — NEJM, 2003Ruling out DVT [1]
CLOTS Trials Collaboration — Lancet, 2009Stockings after stroke [2]
CLOTS Trials Collaboration — Lancet, 2013Pneumatic compression after stroke [3]

References

  1. Wells PS, Anderson DR, Rodger M, et al. Evaluation of D-dimer in the diagnosis of suspected deep-vein thrombosis. New England Journal of Medicine. 2003;349(13):1227–1235. doi:10.1056/NEJMoa023153 PMID 14507948 Randomised controlled trial
  2. CLOTS Trials Collaboration; Dennis M, Sandercock PAG, Reid J, et al. Effectiveness of thigh-length graduated compression stockings to reduce the risk of deep vein thrombosis after stroke (CLOTS trial 1): a multicentre, randomised controlled trial. Lancet. 2009;373(9679):1958–1965. doi:10.1016/S0140-6736(09)60941-7 PMID 19477503 Randomised controlled trial
  3. CLOTS Trials Collaboration; Dennis M, Sandercock P, Reid J, et al. Effectiveness of intermittent pneumatic compression in reduction of risk of deep vein thrombosis in patients who have had a stroke (CLOTS 3): a multicentre randomised controlled trial. Lancet. 2013;382(9891):516–524. doi:10.1016/S0140-6736(13)61050-8 PMID 23727163 Randomised controlled trial

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Reviewed by the Physiotherapist India Team. · Human Physiology contents