Heparin, Questions and Answers


Heparin is an anticoagulant drug. Anticoagulants are medicines that keep your blood from clotting as easily as usual. There are 2 kinds of heparin:

  • Unfractionated heparin.

  • Low molecular weight heparin (LMWH).


When blood clots, it turns from a liquid into a solid. Blood clotting keeps the body from losing too much blood from wounds, burns, or at the time of delivering a baby. Anticoagulants are often called blood thinners. But what they actually do is increase the time it takes a blood clot to form.


Heparin and LMWH are used in hospitals or clinics because they work right away. In the hospital, these drugs are used:

  • During heart valve surgery.

  • After hip replacement surgery.

  • For serious cases of blood clots and heart attacks.

The right amount and type of anticoagulant can prevent many problems.


When giving heparin or LMWH in the hospital or when giving LMWH as an outpatient, there may be a need for regular blood tests. The goal of heparin therapy is to lessen the clotting tendency of blood, but not to prevent clotting completely. The effect of heparin on the blood's ability to clot must be watched carefully using laboratory blood tests.

The anticoagulation effect of unfractionated heparin can be reliably monitored by a blood test. It is called the activated partial thromboplastin time (aPTT). The higher the aPTT, the greater the chance for side effects of bleeding.

The anticoagulation effect of LMWH is not reflected by the aPTT. Monitoring LMWH activity requires getting a blood test called an antifactor Xa level. Periodic monitoring as recommended by your caregiver may be suggested if LMWH is given during pregnancy. Routine monitoring for nonpregnant women is usually not needed.


  • Because anticoagulants thin your blood, severe bleeding may occur from any tissue or organ. Symptoms of the blood being too thin may include:

  • Bleeding from the nose or gums that does not stop quickly.

  • Unusual bruising or bruising easily.

  • Swelling or pain at an injection site.

  • A cut that does not stop bleeding within 10 minutes.

  • Continual nausea for more than 1 day or vomiting blood.

  • Coughing up blood.

  • Blood in the urine which may appear as pink, red, or brown urine.

  • Blood in bowel movements which may appear as red, dark or black stools.

  • Sudden weakness or numbness of the face, arm, or leg, especially on one side of the body.

  • Sudden confusion.

  • Trouble speaking (aphasia) or understanding.

  • Sudden trouble seeing in one or both eyes.

  • Sudden trouble walking.

  • Dizziness.

  • Loss of balance or coordination.

  • Severe pain, such as a headache, joint pain, or back pain.

  • Fever.

  • Bruising around the injection sites may be expected.

  • Platelet drops, known as "thrombocytopenia," can occur with enoxaparin use. A condition called "heparin-induced thrombocytopenia" has been seen. If you have had this condition, you should tell your caregiver. Your caregiver may direct you to have blood tests to monitor this condition.

  • Do not use if you have allergies to the medication, heparin, or pork products.

  • Other side effects may include mild local reactions or irritation at the site of injection, pain, bruising, and redness of skin.

  • Other body systems can be affected by heparin. In addition to bleeding, patients can develop thinning of the bones (osteoporosis) over a long period of time.

  • An advantage of LMWH over unfractionated heparin is that all of the side effects noted above are less frequent.


Giving an anticoagulant (either heparin or LMWH) to a pregnant woman must be considered if the woman:

  • Develops a blood clot while pregnant.

  • Becomes pregnant while being treated for a blood clot.

  • Has a past history of having a blood clotting problem that had no specific cause.

  • Has a known hereditary problem that predisposes her to blood clotting problems.

  • Has certain known diseases affecting ligaments, tendons, skin, and other "connecting" tissues (connective tissue diseases).

Treatment with LMWH has the advantages of:

  • More convenient dosing.

  • It is given as a shot rather than through an IV that may be required for heparin.

  • Longer lasting effects.

  • Frequency of monitoring is less than that required for unfractionated heparin.

Unfortunately, there are also possible disadvantages to LMWH. The longer lasting effect could contribute to a bleeding problem. This includes a concern about bleeding when an anesthesiologist is asked to give a woman epidural anesthesia during delivery. Many anesthesiologists are hesitant to give this type of anesthesia if the woman has gotten LMWH within 24 hours of the time of delivery. In addition, the effects of LMWH are not completely reversible with the drug, protamine. It can reverse the effect of unfractionated heparin though.

LMWH should not be used in a pregnant woman who has:

  • A blood clot in the lung (pulmonary embolism).

  • A mechanical heart valve.


For individuals who are being treated in the hospital, unfractionated heparin may be started first. After getting the full effect of unfractionated heparin, there may be a switch to LMWH. LMWH can be continued at home after you receive instructions on how to give the shot.

LMWH is given to individuals who:

  • Are starting preventative treatment.

  • Have a condition not requiring treatment in the hospital.


  • Due to the complications of anticoagulants, it is very important that you take your anticoagulant as directed by your caregiver. Anticoagulants need to be taken exactly as instructed. Be sure you understand all your anticoagulant instructions.

  • Changes in medicines, supplements, diet, and illness can affect your anticoagulation therapy. Be sure to inform your caregivers of any of these changes.

  • While on anticoagulants, you will need to have blood tests done routinely as directed by your caregivers.

  • Be careful not to cut yourself when using sharp objects.

  • Avoid heavy or variable alcohol use. Consume alcohol only in very limited quantities. General alcohol intake guidelines are 1 drink for nonpregnant women and 2 drinks for men per day. (1 drink = 5 ounces of wine, 12 ounces of beer, or 1 ½ ounces of liquor). A sudden increase in alcohol use can increase your risk of bleeding. Chronic alcohol use can cause warfarin to be less effective.

  • Limit physical activities or sports that could result in a fall or cause injury.

  • It is extremely important that you tell all of your caregivers and dentist that you are taking an anticoagulant, especially if you are injured or plan to have any type of procedure or operation.

  • Follow up with your laboratory test and caregiver appointments as directed. It is very important to keep your appointments. Not keeping appointments could result in a chronic or permanent injury, pain, or disability.