Evaluating the Presence of Blood Clots in People With Heparin-Induced Thrombocytopenia (HIT) (The HOT Study)
Evaluating the Presence of Blood Clots in People With Heparin-Induced Thrombocytopenia (HIT) (The HOT Study)
Heparin-induced thrombocytopenia (HIT), a condition characterized by low platelet levels and
 possible blood clots, occurs in a small number of people after treatment with the drug
 heparin. Some people with HIT may show symptoms of a blood clot at the time of HIT diagnosis,
 but in another form of HIT, known as isolated HIT, people do not show blood clot symptoms
 even though they might have a blood clot. This study will use ultrasound tests to evaluate
 the presence of blood clots at the time of an HIT diagnosis and in the following month.
Heparin is a blood thinning medication that is often prescribed to treat or prevent blood
 clots. HIT is a life-threatening immune disorder that occurs in 1 to 3% of people who receive
 heparin. In this disorder, heparin does the opposite of what it is supposed to do: it
 promotes new blood clot formation, rather than preventing it. In people with HIT, the immune
 system triggers a response against heparin, leading to the destruction of platelets and a low
 platelet count, which is known as thrombocytopenia. Symptoms usually occur between 5 to 14
 days after starting heparin therapy. Isolated HIT is a form of the condition that occurs when
 people have a low platelet count, but there is no sign of a blood clot, or thrombosis.
 Several small research studies have shown that at the time of isolated HIT diagnosis, between
 15 to 50% of people actually have asymptomatic thrombosis, which means that they are not
 showing any signs of a blood clot, but in fact have one. In the month following HIT
 diagnosis, up to 50% of people experience symptomatic thrombosis, which means that they are
 showing signs of a blood clot. It is not currently known how to best treat isolated HIT and
 how to test for unrecognized blood clots. This study will use ultrasound imaging to evaluate
 the number of people who have asymptomatic thrombosis at the time of isolated HIT diagnosis
 and to determine the rate of symptomatic and asymptomatic thrombosis in the following month.
 The results of this study will assist researchers in assessing current approaches to treating
 isolated HIT and in designing new clinical trials. By exploring the use of non-invasive
 evaluation techniques in people with HIT, thrombosis research in HIT will move forward,
 similar to thrombosis research in other medical conditions.

 This 29-day study will enroll hospital patients who have a diagnosis of HIT but show no signs
 of a blood clot at the time of HIT diagnosis. On Day 1, participants will undergo blood
 collection and an ultrasound. While participants are in the hospital, study researchers will
 review participants' medical records on a daily basis to collect data on current medications,
 medication compliance, symptoms, bleeding, thrombosis complications, and laboratory test
 results. Once participants leave the hospital, this data will be collected at least once a
 week through phone calls with the participant and/or the treating physician. On Day 29,
 participants will undergo a repeat ultrasound and blood collection.
Inclusion Criteria:

 -  In the 72 hours prior to study entry, participant has been diagnosed with "isolated
 HIT," as defined by an unexplained platelet count drop of over 50% that occurs after
 exposure to UFH (UnFractionated Heparin)/LMWH (Low Molecular Weight Heparin) at any
 time in the 4 to 14 days before the positive heparin-PF4 antibody test was sent(even
 if the person is no longer on UFH/LMWH)

 -  Currently hospitalized

 -  Available for study follow-up for at least 28 days after study entry

 -  No contraindications to ultrasound examination of upper and lower extremities

 -  For participants less than 7 years old, no contraindications to ultrasound examination
 of abdomen

 -  Participants are eligible whether or not they are receiving any therapy for isolated
 HIT

 Exclusion Criteria:

 -  Documented new venous or arterial thrombosis while on heparin

 -  Pregnant

 -  Ongoing active bleeding (as determined by the site investigator)

 -  Currently using a extracorporeal membrane oxygenator, chronic veno-venous
 hemofiltration, left ventricular support device, intra-aortic balloon pump, or any
 other mechanical heart pump

 -  Coronary artery bypass surgery occured within 96 hours prior to the time when the
 positive HIT test was drawn