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In this clinical scenario, we have a 63-year-old male with atrial fibrillation. He's on the cardiac wards, and so he's at atrial fibrillation, unstable. So he was placed on a heparin trip at this facility, and he was noted for low platelets. So another fact that you would want to know is, and the questions you're talking to me is how long has he been on heparin for? We're gonna say five days. So what is a potential diagnosis that we have? Just think about it before we get to the next part of the lecture. So we're discussing heparin-induced thrombocytopenia HIT. And there's two types of HIT. Type one is a non-immune. And you say, What's going on with this? This is timing is usually one to four days after initiating heparin. And antibody status, there's no antibodies. Platelet count is greater than 100,000. Clinical outcome in action, no thrombosis, no need to stop heparin. And let's talk about it. It's a direct platelet effect of heparin on factor four on the surface, causing mild clumpling, but not antibody formation. It's not immune, it's just a direct pharmacological effect on the platelet, not an autoimmune response. Very important. Timing occurs within one to two days of heparin administration. And it's mild and transient. Platelet count slightly drops, rarely below 100,000, and returns, even if the heparin therapy continues. There's no clotting risk. This is the important thing. Unlike the more serious type 2 hit, this condition isn't associated with dangerous blood clots. Now let's talk about type 2. And this is important. This is dangerous. This is life-threatening. Where we have autoantibodies to platelet factor 4 in heparin complex. Usually the timing occurs 5 to 10, 15 days after starting heparin, and that's what we discussed. This patient had been on heparin for five days. Mechanism is caused by autoantibodies to platelet factor 4, complex with heparin. Risk for unfractionated heparin is 1 to 3%. For lower risk for low molecular weight heparin is 0.8%. So that's why you see a lot of facilities go to or a lot of providers order low molecular weight heparin instead of unfractionated heparin. Now let's talk about the 4T scoring system. And you say, why do we need to do this? We're going to send some labs out. Well, the lab we sent out, that's the important one that helps us. In most cases, it takes time for it to come back. Depending on what part of the country you're on, what lab system you're using, sometimes it takes about a week to come back. So you don't have that time to kind of figure out what you're going to do for your patient, how you're going to treat that patient who's there in front of you. You can't go, well, it's going to be a week before I get to the lab. So we're going to continue what we're doing, and it can cause harm to you, but we're good to go. And give them a big thumbs up. No, you can't do that. So this is where we start to use information that we can do bedside and basically do a calculation. This is the 4T scoring system. And basically, you can go through this, and there's multiple calculators out there similar to this. This is one that's probably used more than others. And you can use this on any of your calculators that you have on your uh tablet or phone device. And what you're doing is you're getting a scoring system. In this one, we have a high probability if we have six to eight points. So you're just basically going through and you're looking through is there thrombocytopenia, when did they fall, giving the time period? Is there thrombosis and other causes? So, how would you know is there other causes that could be apparent for this patient? Um maybe they have malignancy, and that can cause us to have a high probability of having clots. Thrombosis, you would see possibly on CT imaging or DVT ultrasounds. High probability would be six to eight points, and this scoring system intermediate would be four to five points, and then low probability is less than equal to three points. So this would give you an idea of what action you need to take for this patient. Let's continue our discussion on heparin-induced thrombocytopenia. Now, remember in heparint uh induced thrombocinia, we see a 30% risk of thrombosis. About 75% of them will be in the venous system and 25% in arterial. What are some risk factors when we say heparin greater than four, five days? Five days is probably more correct if patients has had a surgery, increased risk. Using heparin on fractional heparin instead of low molecular weight heparin. So what is a diagnostic indicator? Would be platelet count greater than 50% from baseline, is suggestive diagnosis. Now you said, why did we use that scoring system? Well, the gold standard for determining for if patient is having HIIT is the ELISA 4 PF4 heparin antibodies. And this is a functional essay. It's a serotonin release essay. It's the gold standard. Now, it's a technically challenging test that requires special handing of platelets and radioisotopes, which limits its accessibility, increases turnaround times, meaning it takes time for it to do, and there's not that many places to do it. So depending where you are in the countries, you may have to send it out. So you have the transit time and the time it takes to get the answer back. But also the test itself is a little bit challenging. So the donor platelets are incubated with a radioactive serotonin, just like Spider-Man radioactive serotonin, right? And they're taken up and stored in the secretory platelets. This is, and then the platelets are washed and removed to remove the excess of radioactive uh radioactive serotonin. That's a radioactive tracer that's placed on the serotonin. The serotonin release assay generally takes about two to four days for the analytic time. With the turnaround time, the specimen can result sometimes three to seven days. Now, if you add a holiday into those mix, it takes a little bit longer. I know it's not supposed to, but it does. It does take longer in the holidays. And at Dirty Word weekends, if you send it out, it may not get there during the weekend and it may not be worked on. I know it's not supposed to, but it does. So this is why you have to say is what am I gonna do to treat this patient? Because I'm not gonna get the serotonin release assay back right away. Now let's talk treatment for a hit. That's why we use a scoring system because it's gonna take time for that serotonin release assay to come back. So then you come up with your plan of action, and the first thing you're gonna do is initiate in the anticoagulation. So you're gonna stop the heparin. Number one, stop the heparin, stop the heparin. And then you're gonna initiate anticoagulation with the direct thrombid inhibitors, liperidin, agatroband, bivil uh bivalirudin. Those are your ones again. Now, then you would initiate a transition phase. But here again, let's go with what the new evidence is. DOACs. Now, this data from 12 publications across 36 patients. So not robust data, but it's starting that DOACs are an acute phase of hit, maybe safe and effective treatment option for patients. Now, initiating DOAC does not require platelet recovery, so we'll go back to this and transition when the patient is clinically stable. So when the patient is stable, you initiate the DOAC and there's no overlap. You start DOAC within two hours of stopping one of the direct anticoagulations, your direct thrombin inhibitors. Pretty nice because it can take some time for these patients to get them out of the hospital. So let's go back to the old school ways we initiate the direct thrombin inhibitors. We have a transition place and we wait for the platelets count to become greater than 100,000. Then we start warfarin for four weeks, and then you're gonna determine how long you're gonna continue the warfarin for. Now it says no heparin for the next six months. Now, this may be years because they may hold on to the antibody. So it can be years or never starting heparin again. So this is how you would treat someone with HIIT and to get them back into the game and get them back home.