Blood in Urine..yes, I saw a Dr for this

I've peed blood after several major races (very difficult marathons, HIM) and also had it checked out. Doc also chalked it up to bladder wall friction and/or kidney "bruising" (also had what seemed to be yucky shoulder-ish pain one mary but was kidney, probably, ow) and like yours, was very unconcerned. Didn't even bother to go back for any med tests/consult after the third time.

Don't know if that helps, but yes, you have a fellow experiencer, and I know personally of quite a few others that this has happened /happens to.

It has happened to me 3-4 times over my athletic career (first time in about 1983).

Almost always from a hard run, but usually not the hardest ones...Like you, just one urination.

The last time was from rhabdo after a stupid crazy squat workout when I hadn't been doing squats on a regular basis.  almost needed medical treatment for the leg trauma....it was horrible.

For a few years I've been on anticoagulants but it hasn't happened during this time.

YES!  Me!!!! 

In Nov 2010, as I was training for a HM and started running in a new pair of shoes I regularly started noticing blood in my urine, again only after the first post run urination.  I searched the boards here and ST, and most responses I found chaulked it up to dehydration or "Dude, you're dying of cancer". I talked to my Dr at my yearly appt in Dec and she felt strongly that it is bc the bladder is a bloody, mucous-y (is that a word?) mess and not worry about it. 

In April of 2011 I went back to the Dr bc I was still experiencing this (still regularly but not every run) it was now accompanied by a sharp pain in my lower abdomin (next to my ovaries).  I had blood tests, MRIs, you name it and nothing.  Dr just said to monitor it.  Shortly thereafter it went away.  Every now and then the same thing happens but not regularly anymore.

Things I have started to do differently since this first happened; hydrate more before running (I used to be really, really awful about hydrating) and I've actually changed my diet pretty dramatically to exclude any processed foods and trying to exclude gluten and dairy as much as possible.  The abdominal pain has also gone away except for random occaisions.

So, yes, you are not alone but I do wish there was more explanation. 

I'm a Gynecologist, so not an expert on bladders and endurance athletics per se, but the bladder is pretty easy to irritate.  When it becomes irritated and inflamed you can see blood in your urine.  It always needs to be evaluated.  The most common cause of blood in the urine (hematuria) is a bladder infection, and next is a kidney stone.  But more serious problems like kidney or bladder cancer can also cause it.  It sounds like you had a pretty good evaluation including a cystoscopy which is pretty good for ruling out bladder cancer.  Once the bad has been ruled out it is just a matter of trying to explain it, and I would bet it is simply with some longer runs it suffers from some physical trauma. 

Also remember that it does not take much blood to make your urine look very bloody.  A few drops of red food coloring can make a whole gallon of water look pretty red.  Urine and blood are the same. 

And for the necessary legal disclaimer - no providing a diagnosis or medical advice, just hopefully adding a plausible explanation! 

Good Luck!

I raced a half marathon in Jan.  I urinated blood immediately after and continued to do so (less and less each time) for the next couple of hours.  I was fine by the evening.

That race was on a Saturday; the Monday following that I had an easy run with some hill repeats.  Afterward, I had the same issue.  That was the last time though.  No more issues since then.