Section 4: Unfractionated Heparin (UFH) and Heparin-induced Thrombocytopenia (HIT)

The following does not relate to intra-operative / procedural use of unfractionated heparin and only covers use of heparin infusions for the purpose of therapeutic anticoagulation. Where suitable alternatives exist, these should be used in favour of unfractionated heparin infusions. However, there are circumstances where unfractionated heparin infusions may be the most suitable form of anticoagulation. These include when therapeutic anticoagulation cannot be safely omitted or deferred in the following contexts:

• Immediate anticoagulation is required e.g. post-vascular intervention.
• Immediately following use of systemic fibrinolytic agents.
• Urgent reversal may be needed e.g. known potential bleeding site, very recent surgery.
• CrCl < 30ml/min and surgery is required within 24 hours.

When prescribing unfractionated heparin, use the NHS Borders Heparin Adult Infusion Chart:

https://rightdecisions.scot.nhs.uk/media/1902/heparin-adult-infusion-chart-sept-2022-24.pdf

The initial loading dose (if applicable) should be prescribed on the front of the patient’s Kardex as a “Once Only” medicine. The heparin infusion must be prescribed on the linked infusion chart and as a regular medicine in the patient’s Kardex with dose “As Per Chart”. Heparin infusion should be started immediately after a loading dose is administered.

Please note that in NHS Borders, unfractionated heparin is available in a ready-made concentration of 1000 units/ml. DO NOT DILUTE THIS PREPARATION.

Changes of the rate of heparin infusion depend on the results of unfractionated heparin assays, and monitoring requirements are described in the infusion charts detailed above.

For advice on switching from unfractionated heparin to LMWH or DOAC when clinically appropriate, discuss with Haematology team.

Within NHS Borders, UFH monitoring is carried out using Activated Partial Thromboplastin Ratio (APTR) monitoring. Other centres may use Anti-Xa level monitoring, however Anti-Xa levels are not carried out within NHS Borders Laboratories and thus cannot be obtained in a timely manner for UFH monitoring.

The appropriate test to request on TrakCare for monitoring of unfractionated heparin is an “APTR (ratio)” test (this will also appear when searching for “Heparin”). Please note that low molecular weight heparin (LMWH) assays are not equivalent and should not be ordered for this purpose.

Dose adjustment instructions, based on the APTR result, are included on the heparin infusion chart.

Monitoring of unfractionated heparin assay (APTR) is required 6 hours after starting a heparin infusion and 6 hours after every change of rate, plus at least once every 24 hours when the rate of infusion is unchanged.

As the half-life of unfractionated heparin is about 1 hour, it is usually sufficient to stop the heparin infusion without administration of a specific reversal agent. If bleeding is severe, consider protamine sulphate (1mg for every 100 units heparin given in previous hour). Give slowly at rate not exceeding 5 mg/min, maximum single dose of 50 mg.

Note - there is a risk of anaphylaxis with protamine administration.

HIT is a serious complication of heparin (and LMWH) therapy. There is currently no NHS Borders pathway for management of HIT. Please refer to the NHS Lothian diagnostic and management pathway for guidance at:

http://intranet.lothian.scot.nhs.uk/Directory/Haematology/policy/Documents/Heparin-induced%20Thrombocytopenia%20Clinical%20Guideline.pdf

Argatroban is a non-heparin anticoagulant that may be used in management of HIT. Fondaparinux is also another treatment option for HIT. The NHS Borders Adult Argatroban Infusion Chart can be found on the intranet at:

Argatroban Infusion Chart

Platelet count monitoring in patients receiving heparins

The incidence of HIT is significantly higher following exposure to unfractionated heparin than it is following exposure to LMWH only. However, the incidence of HIT with LMWH is increased in patients undergoing cardiac surgery.

The most common type of HIT is immune-mediated and does not normally develop until 5-10 days after heparin exposure unless the patient has been exposed to heparin in the previous 100 days. A baseline platelet count should be checked prior to commencing unfractionated heparin or LMWH.

Post-operative patients, including obstetric cases, receiving unfractionated heparin should have platelet count monitoring performed daily from days 4-14, or until unfractionated heparin is stopped. 

Post-cardiopulmonary bypass patients receiving LMWH should have platelet count monitoring performed daily from days 4-14 (if an in-patient) or until LMWH is stopped. If an outpatient, then FBC checks every 2-3 days are advised until day 14 post-operatively. 

Post-operative patients (other than cardiopulmonary bypass patients) receiving LMWH do not need routine platelet monitoring. 

All post-operative patients including cardiopulmonary bypass patients who have been exposed to unfractionated heparin in the previous 100 days and are receiving any type of heparin should have a platelet count determined 24 hours after starting heparin. 

Orthopaedic, surgical and gynaecology patients discharged on LMWH should be advised of the small risk of HIT, and advised that in the event of general malaise, development of signs and symptoms of venous thrombosis, and development of erythematous or necrotic areas at the site of injection, they should have an urgent FBC check to ensure there has not been a 30% fall in the platelet count from the pre-operative baseline. 

If HIT is strongly suspected or confirmed, all heparins should be stopped and an alternative anticoagulant such as fondaparinux or argatroban should be given.