A practical FY guide to anticoagulation on the ward — VTE prophylaxis, LMWH, DOACs, warfarin, renal function, bleeding risk and common prescribing pitfalls.
Anticoagulation is one of those areas that can feel more complicated than it needs to be during FY.
One patient is on prophylactic low-molecular-weight heparin, another is taking apixaban for atrial fibrillation, a third is receiving treatment-dose anticoagulation for a pulmonary embolism, and someone else has a mechanical heart valve and a warfarin chart.
The safest way to approach anticoagulation on the ward is not to memorise every regimen.
Start by asking a few basic questions: Why is this patient anticoagulated?
Is the dose prophylactic or therapeutic?
What is their renal function and weight?
Are they bleeding?
And is there a reason today's dose should be changed, withheld or escalated?
The key distinction
VTE prophylaxis prevents a clot in an at-risk hospital patient.
Therapeutic anticoagulation treats an existing clot or prevents systemic embolism in conditions such as atrial fibrillation.
Mixing up prophylactic and treatment doses is a major prescribing error.
1. First work out why the patient is anticoagulated
Common ward indications include:
- VTE prophylaxis during a hospital admission
- Treatment of a confirmed deep vein thrombosis (DVT) or pulmonary embolism (PE)
- Stroke prevention in atrial fibrillation
- Mechanical prosthetic heart valves, usually with a vitamin K antagonist such as warfarin
- Other specialist indications where the anticoagulation plan may be highly individualised
Do not assume that every anticoagulant on a drug chart is being used for the same reason. The indication determines the drug, dose, duration and monitoring.
2. VTE prophylaxis: the common everyday job
Hospital admission increases VTE risk, so patients should have both VTE risk and bleeding risk assessed promptly after admission. Where pharmacological prophylaxis is indicated, it should normally be started as soon as possible and within 14 hours of admission.
Before prescribing prophylaxis, check:
- Has a VTE and bleeding risk assessment actually been completed?
- Is the patient already receiving therapeutic anticoagulation?
- Is there active bleeding or another important bleeding risk?
- What is the platelet count?
- What is the renal function?
- What is the patient's weight, particularly if they are at an extreme of body weight?
- Is there a history of heparin-induced thrombocytopenia (HIT)?
- Is a procedure planned that changes the anticoagulation plan?
Low-molecular-weight heparin (LMWH) is commonly used for pharmacological prophylaxis.
In renal impairment, the choice and dose may need adjustment; NICE allows either LMWH or unfractionated heparin in this setting.
Follow your local prescribing protocol for the actual preparation and dose.
3. LMWH: prophylactic dose is not treatment dose
LMWH appears everywhere in hospital medicine, but the dose depends on what you are trying to achieve.
A prophylactic dose is intended to reduce hospital-acquired VTE risk.
A treatment dose is used for established or strongly suspected thromboembolism and is usually weight-based.
Before prescribing treatment-dose LMWH, make sure the patient's weight and renal function are known. Also review the haemoglobin and platelet count and ask whether there is active or recent bleeding.
Heparins can cause bleeding and, more rarely, HIT.
A falling platelet count in a patient exposed to heparin should not be ignored.
If HIT is suspected, stop and seek senior or haematology advice rather than simply switching between different heparin products.
4. DOACs: simple to prescribe, easy to prescribe wrongly
Direct-acting oral anticoagulants (DOACs) include apixaban, rivaroxaban, edoxaban and dabigatran. They do not use INR monitoring in the way warfarin does, but that does not mean they require no thought or monitoring.
Before prescribing or continuing a DOAC, check:
- The indication
- The exact drug and dose
- Renal function
- Weight and age where these affect dosing
- Relevant liver function
- Other medicines that may increase bleeding or interact
- Whether the patient has active bleeding, significant anaemia or a recent bleeding event
- When the last dose was taken, especially if a procedure is planned
A particularly important FY point is that DOAC dosing can change with the indication and stage of treatment.
For example, a regimen used for acute VTE may not be the same as the regimen used for atrial fibrillation.
Do not copy a dose from another patient or assume that “apixaban is apixaban”.
Check the current BNF and the documented plan.
For confirmed proximal DVT or PE, NICE recommends anticoagulation for at least 3 months and lists apixaban or rivaroxaban as first options for many patients, with alternatives depending on clinical circumstances.
5. Warfarin: think INR, indication and plan
Warfarin has a narrow therapeutic range and its effect is monitored using the INR. The target INR depends on the indication, so never assume every patient has the same target.
Before prescribing a warfarin dose, check:
- Why the patient takes warfarin
- Their target INR
- The latest INR and recent trend
- The most recent dosing plan or anticoagulation chart
- Whether new medicines, acute illness or dietary changes may have altered control
- Whether there is bleeding or an upcoming procedure
Do not guess a warfarin dose because the patient “usually takes 3 mg”.
If the INR is unexpectedly high or low, work out why and follow the appropriate anticoagulation plan.
Major bleeding or a markedly excessive INR needs urgent senior assessment and a reversal strategy rather than routine ward-level dose adjustment.
Mechanical heart valves are a particularly important exception to the modern move towards DOACs. DOACs should not be used as a substitute for the established anticoagulation plan in a patient with a mechanical valve.
6. Atrial fibrillation: anticoagulation is about stroke prevention
For atrial fibrillation, the question is whether the patient's stroke risk justifies anticoagulation. NICE uses the CHA₂DS₂-VASc score to assess stroke risk and the ORBIT score to assess bleeding risk.
NICE recommends offering anticoagulation to people with atrial fibrillation and a CHA₂DS₂-VASc score of 2 or more, and considering anticoagulation for men with a score of 1, after discussing risks and benefits. A DOAC is generally preferred when appropriate.
As an FY, you will often be continuing an established plan rather than making the long-term decision alone.
New AF, recent stroke, active bleeding, severe renal impairment or uncertainty about valve disease are good reasons to involve a senior before starting or changing anticoagulation.
7. The “before I sign” anticoagulation check
A useful mental checklist is:
- INDICATION — Why are they anticoagulated?
- INTENSITY — Prophylactic or therapeutic?
- DRUG — LMWH, DOAC, warfarin or something else?
- DOSE — Is it correct for this indication?
- KIDNEYS — Does renal impairment change the choice or dose?
- WEIGHT — Is the patient very small, very large or receiving weight-based therapy?
- BLOOD — Haemoglobin and platelet count; any evidence of bleeding?
- PROCEDURE — Is an operation, lumbar puncture or other invasive procedure planned?
- LAST DOSE — When was the anticoagulant last given?
- PLAN — What needs monitoring or handing over?
One-line rule: Before prescribing an anticoagulant, know the indication, intensity, renal function, bleeding risk and what happens next.
8. The anticoagulated patient who starts bleeding
If a patient taking an anticoagulant develops significant bleeding, do not simply delete the next dose and move on.
Assess the patient, identify the likely source and severity, check observations and obtain appropriate blood tests.
Establish exactly which anticoagulant they are taking and when the last dose was given.
Significant bleeding, haemodynamic instability, suspected intracranial bleeding or a major fall/head injury in an anticoagulated patient should trigger urgent senior assessment.
Reversal depends on the anticoagulant and clinical circumstances, so use the current BNF and the appropriate local emergency pathway rather than trying to improvise.
What dose?
When was the last dose?
Why are they anticoagulated?” are four questions worth answering early.
9. Procedures: do not stop anticoagulation casually
You may be asked to withhold anticoagulation because a patient is having a procedure. The correct interruption depends on the drug, renal function, bleeding risk of the procedure and the patient's thrombotic risk.
Do not make up a stop/restart interval from memory.
Check the documented procedural plan, current BNF and local policy, and ask the relevant senior team if the plan is unclear.
This is particularly important for mechanical valves, recent VTE and patients receiving therapeutic anticoagulation.
10. A practical FY example
You are asked to prescribe “the usual enoxaparin” for a patient admitted overnight. Before clicking prescribe, you notice apixaban on their regular medication list.
Your thought process should be:
- Why are they on apixaban? Atrial fibrillation.
- Was it intentionally withheld on admission? No clear documentation.
- Are they bleeding? No.
- Is a procedure planned? No.
- What is the renal function? Stable.
- Do they need additional prophylactic LMWH? Do not assume so.
Instead of automatically prescribing LMWH, clarify whether the apixaban should be continued. This avoids accidental double anticoagulation and turns a routine prescribing job into a safe clinical decision.
The FY anticoagulation rule
INDICATION → PROPHYLACTIC OR THERAPEUTIC → DRUG → DOSE → KIDNEYS → WEIGHT → BLEEDING → PROCEDURE → MONITOR / HAND OVER
Anticoagulation becomes much easier when you stop thinking of it as one topic.
Your job on the ward is usually to recognise what the anticoagulant is for, make sure the prescription matches the indication and patient, identify bleeding or renal-function problems, and escalate when the situation is outside routine prescribing.
If the indication is unclear, the dose looks unusual, renal function is changing, the patient is bleeding, a procedure is planned, or you are considering reversal or interruption of therapeutic anticoagulation, involve a senior early.
Educational note: This article is intended for Foundation doctors as an educational guide. For exact anticoagulant doses, dose adjustments, contraindications, reversal and peri-procedural timing, use the current BNF, NICE guidance and your local anticoagulation policy.
