Heparin reduces the risk of blood clot formation. It is indicated for patients with deep vein thrombosis, pulmonary embolism, and other clotting conditions. Unfractionated heparin should be monitored to adjust the dose to maintain levels in the target therapeutic range because heparin overdose can lead to life-threatening bleeding. Activated partial thromboplastin time (aPTT) is the test of choice to monitor unfractionated heparin. An aPTT of 1.5 to 2.5 times the upper limit of the normal range is widely accepted for maintenance therapy. Platelet count is a test that determines the number of platelets in the blood, normally 150,000 to 400,000/mL. Bleeding time is a test that determines the functions of the platelet, particularly on its ability to coagulate. Heparin’s main function is to inhibit clotting factors, not platelets. Standard bleeding time is 1-9 minutes. Erythrocyte sedimentation rate (ESR) is a test that determines the rate of red blood cells to form sediments in an hour. It is used to detect inflammation.