What labs should be monitored in a patient on enoxaparin (low molecular weight heparin) and heparin (unfractionated heparin)?

From the Guidelines

For patients on enoxaparin and heparin, monitoring should include complete blood count (CBC) periodically to assess for thrombocytopenia, renal function tests (BUN, creatinine) to assess for kidney dysfunction, and baseline coagulation studies (PT/INR, aPTT) and CBC before initiation. For patients on enoxaparin (low molecular weight heparin), routine monitoring of anti-factor Xa levels is generally not required, but may be considered in special populations such as pregnant patients, those with renal impairment, extremes of body weight, or children 1. For patients on unfractionated heparin, activated partial thromboplastin time (aPTT) should be monitored regularly, typically 6 hours after initiation and dose changes, then daily once therapeutic, with a target aPTT of 1.5-2.5 times the control value 1. Key considerations include:

• Monitoring for heparin-induced thrombocytopenia (HIT) in patients at intermediate or high risk for HIT, with platelet count monitoring every 2 to 3 days from day 4 to day 14 while receiving heparin 1
• Adjusting the dose of heparin based on aPTT results, while being aware of the potential for heparin resistance and the need for alternative monitoring strategies such as anti-Xa activity in certain patient populations 1
• Considering the use of alternative anticoagulants with lower renal clearance in patients with renal dysfunction 1. Overall, monitoring helps ensure therapeutic anticoagulation while minimizing bleeding risks, and should be tailored to the individual patient's risk factors and clinical presentation.

From the FDA Drug Label

Periodic platelet counts, hematocrits, and tests for occult blood in stool are recommended during the entire course of heparin therapy, regardless of the route of administration When heparin is given by continuous intravenous infusion, the coagulation time should be determined approximately every four hours in the early stages of treatment. Dosage is considered adequate when the activated partial thromboplastin time (APTT) is 1.5 to 2 times normal or when the whole blood clotting time is elevated approximately 2.5 to 3 times the control value. Adjust heparin to maintain aPTT of 60 to 85 seconds, assuming this reflects an anti-Factor Xa level of 0.35 to 0.70.

The labs that should be monitored when a patient is on enoxaparin and heparin are:

• Platelet counts
• Hematocrits
• Tests for occult blood in stool
• Activated partial thromboplastin time (APTT)
• Whole blood clotting time
• Anti-Factor Xa level 2 2

From the Research

Laboratory Monitoring for Heparin-Induced Thrombocytopenia

When a patient is on enoxaparin (low molecular weight heparin) and heparin (unfractionated heparin), several labs should be monitored to prevent and detect heparin-induced thrombocytopenia (HIT). The key labs to monitor include:

• Platelet count: This is the most important lab to monitor, as HIT is characterized by a decrease in platelet count 3, 4, 5, 6.
• Platelet count baseline: This should be established before starting heparin therapy, and monitoring should focus on the period of highest risk (usually days 5 to 10 after starting heparin) 3.
• Platelet aggregometry: This test can be used to detect the presence of HIT antibodies, which can cause platelet aggregation in the presence of heparin 7.

Frequency of Laboratory Monitoring

The frequency of laboratory monitoring depends on the patient's risk of developing HIT and the type of heparin being used. According to the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy, the following monitoring schedules are recommended:

• For patients receiving therapeutic-dose unfractionated heparin, monitor platelet count at least every other day until day 14, or until heparin is stopped 4.
• For patients receiving postoperative antithrombotic prophylaxis with unfractionated heparin, monitor platelet count every other day between postoperative days 4 to 14, or until heparin is stopped 4.
• For medical/obstetric patients receiving prophylactic-dose unfractionated heparin or low molecular weight heparin, monitor platelet count every 2 to 3 days from day 4 to day 14, or until heparin is stopped 4.

Special Considerations

In patients with a history of HIT, it is essential to monitor platelet count closely, especially during the first weeks of treatment with heparin 6. Additionally, patients who have developed HIT while on unfractionated heparin may be able to safely receive enoxaparin if their plasma does not aggregate platelets in the presence of enoxaparin 7.