IV Unfractionated Heparin (UFH)

There are different concentrations of unfractionated heparin currently available – only the 1000 units/ml preparation should be used at all times. Always consider using a low molecular weight heparin (LMWH), if clinically appropriate unless it is contraindicated, before using unfractionated heparin.

Baseline bloods

  • Coagulation screen
  • FBC (platelet count)
  • Renal function

If any are any abnormalities in coagulation screen, if platelet count <50x109/L, or if eGFR <20ml/min, please contact haematology on call as smaller doses may be required.

Dosing

Initiation Dose:

If the patient has already had treatment dose LMWH or has had an oral anticoagulant (vitamin K antagonist or direct acting oral anticoagulant (DOAC)) within 12 hours, discuss with haematology oncall.

If the patient has had prophylactic LMWH within 12 hours and weighs between 50-100kg, give a bolus of 5000 units UFH IV over 5 minutes.

If the patient has had no LMWH within 12 hours and weighs between 50-100kg, give a bolus of 5000 units UFH IV over 5 minutes.

Maintenance Infusion:

Give UFH at a rate of 18 units/kg/hour, e.g. for a 70kg patient usually ~1200 units/hour (if the patient is at high risk of bleeding, start at 1000 units/hour).

If the patient weighs <50kg or >100kg, discuss with haematology oncall.

Monitoring

  • Target APTT ratio range is 1.8 to 2.8.
  • Check APTT ratio after 6 hours. Adjust infusion rate according to APTT ratio (see table 1 below).
  • If a dose adjustment is made, recheck APTT ratio after 4 hours.
  • Patients rarely require rates >2ml/hr. If target APTT ratio is not achieved at this rate, monitor anti-Xa levels.
  • Measure the APTT ratio at least once daily when the APTT ratio is in range. Preferably at the same time of day within working hours.

Table 1 – Unfractionated heparin dose adjustment

APTT ratio Unfractionated Heparin Infusion Rate Change
>4 Stop for 60 minutes and recheck APTT ratio, before recommencing at a rate reduced by 300-500 units/hour
3.5-4.0 Stop for 60 minutes and reduce heparin by 200 units/hour
2.9-3.4 Stop for 30 minutes and reduce heparin by 100 units/hour
1.8-2.8 Within target - no change
1.2-1.7 Increase heparin by 200 units/hour
<1.2 Increase heparin by 400 units/hour and give further bolus of 5000 units heparin and repeat APTT ratio after 6 hours. If APTT ratio is still <1.2, discuss with haematology oncall

NOTES

  • A new syringe should be prepared every 24 hours.
  • Check FBC (platelets) on days 0, 1 and 4 and then continue to monitor on alternate days for 2 weeks. If platelets count <100 x109/L or drop in count is >30% of baseline then this is an indication of developing heparin induced thrombocytopenia (HIT). HIT may also present as new thrombosis or skin allergy. If HIT is suspected, contact haematology oncall for further advice.
  • After IV administration heparin has a very short half-life. However protamine can be used to reverse the effects of heparin. Contact haematology oncall for advice prior to use.

Contact details

During and outwith working hours: Haematology oncall through hospital switchboard.

 

Guideline reviewed August 2025
Page updated April 2026



;