Hematocrit and Hydration.

For the last decade I have suffered from polycythemia vera. HRT or no HRT, I require frequent phlebotomy. I have had over 100 phlebos in the last decade...well over. I live and work in the desert, so I am out in 100 degree plus Temps all summer long. So naturally, I become dehydrated from time to time. I have intentionally had my CBC ran when dehydrated the day before phlebotomy to check the number against the next days when I was properly hydrated. I've done this twice. Both times my hematocrit level was 3 points higher when dehydrated as compared to being fully hydrated the next day. My own experience is that the phlebotomy reduces my hematocrit by the same 3 points. I talked to my DR about this and he confirmed that dehydration does indeed increase hematocrit levels, and may do so in some individuals by as much as 6 or 7%. We are talking about normal dehydration not severe. In other words, proper hydration is critical for those of us that suffer from polycythemia no matter it's cause. Stay hydrated fellas. It helps prevent stroke, clots, headaches, and all the other nasty things that having a high hematocrit level can cause.

I learned something from your post. Thanks for sharing!

Thanks for the contribution.

I knew that dehydration can affect hematocrit, so I try to make sure I'm hydrated before my blood work. But I do a pretty bad job overall of staying hydrated on a regular basis and I have high hematocrit issues too. I need to work harder at this. I didn't realize though that it would impact it by 6 or 7 percent! Thank you for sharing this info.

My own experience:

I used to have my blood tested only AM. Before going to the draw, I would drink lots of water (and coffee) to ensure I was properly hydrated -- at least that's what I thought. I would be peeing clear, but I don't think I was really hydrated.

One day I ran the test later in the day 2-3pm and the results were significantly lower.

Here's a recent example:

4/22/16 @ 2:45pm - HGB 15.2, HCT 46.4
4/29/16 @ 8am - HGB 16.1, HCT 48.1

Yes, I know there's a week between them, but this has been the pattern. Now, when evaluating my need for therapuetic phlebotomy, I always get checked in the afternoon.

I've also noticed that my proper blood test from the lab is always a lower number than the finger prick at blood bank.

gallan said:

I've also noticed that my proper blood test from the lab is always a lower number than the finger prick at blood bank.

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Yep, I just had a therapeutic phlebotomy and they said my hematocrit was 56...it's never been that high and was tested at 54 a month or so ago at Labcorp. So I wouldn't trust their number.

Yes, dehydration will absolutely FALSELY elevate your HCT.

To assess, your hemoglobin should be approximately 1/3 of your HCT (or looking at it the other way, your HCT should be approx 3x your HgB). For example, HgB 16, HCT 48.

If your HCT is MORE THAN 3x your hemoglobin, then it is likely that dehydration (of some degree) is falsely elevating your HCT (for example HgB 16, HCT 52).

If your HCT is or close to 3x the HgB level and the HCT is above 51-52, then it is likely that you truly do have an elevated HCT and it is NOT falsely elevated by dehydration.

Thanks Dr. Saya! This is a perfect example of why I love having my consults with him. He doesn't just "go through the numbers" on test results and tell you if they're good or bad. He'll explain exactly what makes them good or bad, and how that particular test result relates to another result on the next page.

Jon H said:

Thanks Dr. Saya! This is a perfect example of why I love having my consults with him. He doesn't just "go through the numbers" on test results and tell you if they're good or bad. He'll explain exactly what makes them good or bad, and how that particular test result relates to another result on the next page.

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You're welcome and I appreciate the kind words, Jon!