Please note: this guideline has exceeded its review date and is currently under review by specialists. Exercise caution in the use of the clinical guideline.

IV Unfractionated Heparin (UFH)

Always consider using a low molecular weight heparin (LMWH), e.g. dalteparin, if clinically appropriate unless it is contraindicated before using unfractionated heparin.

Baseline monitoring

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

If any are abnormal, please contact a haematologist as smaller doses may be required.

Dosing

Loading Dose:

See table 1 below for dosing. Use undiluted heparin 1000 units/ml vial – IV bolus over 5 minutes. 

Initial Infusion:

See table 1 below for dosing. Draw up 20,000 units in 20ml undiluted heparin solution for infusion (concentration 1000 units/ml) and administer via an infusion pump. Choose heparin 1000units/ml from the drug library on the infusion pump.

Table 1 – Unfractionated heparin loading dose and initial infusion rate

Patient's weight Loading dose Infusion start rate
30-39kg 2500 units = 2.5ml 700 units/hour = 0.7ml/hour
40-49kg 3300 units = 3.3ml 900 units/hour = 0.9ml/hour
50-59kg 4000 units = 4ml 1100 units/hour = 1.1ml/hour
≥60kg 5000 units = 5ml 1400 units/hour = 1.4ml/hour

Monitoring

  • Target APTT ratio range is 1.5 to 2.5
  • Check APTT ratio at 4 hours after starting. Adjust infusion rate according to APTT ratio (see table 2 below).
  • After each dose change, wait 4 hours before next checking APPT ratio.
  • Measure the APTT ratio at least once daily once the APTT ratio is in range
    and stable. Preferably at the same time of day within working hours.

Table 2 – Unfractionated heparin dose adjustment

APTT ratio Unfractionated Heparin Infusion Rate Change
>6 Stop for 1 hour and reduce by 500 units/hour (0.5ml/hour)
5.1-6.0 Stop for 45 minutes and reduce by 500 units/hour (0.5ml/hour)
4.1-5.0 Reduce by 300 units/hour (0.3ml/hour)
3.1-4.0 Reduce by 100 units/hour (0.1ml/hour)
2.6-3.0 Reduce by 50 units/hour (0.05ml/hour)
1.5-2.5 No change
1.2–1.4 Increase heparin by 200 units/hour (0.2ml/hour)
<1.2 Increase heparin by 400 units/hour (0.4ml/hour)

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 x 109 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 a Consultant Haematologist 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 Consultant Haematologist for advice prior to use.

 

Guideline reviewed May 2015
Page updated April 2025



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