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I had a heart monitor on for 21 days and just recieved a note from my Dr. to go somewhere for lab testing. I cannot reach my Dr. at the moment. What is TSH w/reflex to FT4 with my diagnose as tachycardia?
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If I read this correctly, you went to your doctor because you've been having tachycardia (rapid heart beat).  Is that correct?  

As gimel told you, both too much and too little thyroid hormone can cause tachycardia.

Have you had tachycardia in the past?  

The TSH test should be considered nothing but a screening test for healthy individuals.  Although many doctors worship it, it's really quite inadequate by itself.  As gimel also pointed out, TSH with reflex to FT4 means that if TSH result is abnormal, they should then test FT4.  They will not test FT3.  Instead of that, I would ask your doctor to order TSH, FT4 and FT3.  That will show you exactly what your thyroid hormones are doing and if it's likely they are causing your tachycardia.        
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TSH is a pituitary hormone.  The purpose of TSH is to stimulate the thyroid gland to produce thyroid hormone.  The reflex to Free T4 means that if the TSH test shows to be high then they will continue and test for Free T4.  Free T4 is one of the two main thyroid hormones, the other being Free T3.  Excessive levels of thyroid hormone can cause tachycardia.  Of course, inadequate levels can also sometimes cause it as well. So, apparently the doctor wants to check for the possibility of thyroid issues.  What, if any, other symptoms do you have?
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