How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Dr. Saha Your Own Question
Dr. Saha
Dr. Saha, Doctor (MD)
Category: Health
Satisfied Customers: 17663
Experience:  35 years of experience
Type Your Health Question Here...
Dr. Saha is online now
A new question is answered every 9 seconds

How much variation can dehydration or over-hydration cause

This answer was rated:

How much variation can dehydration or over-hydration cause in the values of hematocrit and hemoglobin? How many units of variation?

I recently had a hemoglobin of 12.6 down from 14.7 months ago. And hematocrit and RBC were also slightly below normal range. I also had low blood sodium which seems to have been caused by excessive sweating from a heat wave. I did have symptoms of heat exhaustion that day and for several days after.

Can heat exhaustion or sodium/electrolyte depletion, cause the lowered hemoglobin, hematocrit, and RBC count?

Welcome to Just Answer.

Did you take too much fluid?

Thank you.
Customer: replied 4 years ago.

I don't know if I had drank too much fluid. I had been sweating heavily from exercise the day before and I regularly lose large amounts of sodium in my sweat.


If I had been drinking too much fluid could that have caused such a big difference in hemoglobin 12.6, hematocrit 39, and RBC count 4?



Thank you for the information.

Dehydration can increase the level of hemoglobin, hematocrit.

Red cell count can also increase in dehydration.

The opposite effects can occur with overhydration.

When you were losing fluid in sweat, you are likely to be dehydrated.

So it should have different effect.

However, it is difficult to calculate the degree of hydration precisely from those blood levels.

I would suggest to take a repeat test after a few weeks.

You can also check for iron, B 12 levels.

Those would help to detect any deficiency of those factors.

I hope this information helps.

I will be happy to assist, if you need any clarification.

Please press the EXCELLENT/ GOOD FEEDBACK and feel free for any follow up query.

Customer: replied 4 years ago.

It is very possible I was over-hydrated at the time of the test because I felt so awful and felt better from drinking more water.


In May my hemoglobin was 14.7, RBC 5.37, hematocrit 45. This last test hemoglobin was 12.6, RBC 4, hematocrit 39.


Could over-hydration or other effects of possible heat exhaustion cause these values to lower this much?

I you were over hydrated at the time of test, that can lower the results. However, it would not be possible to determine to what degree. In case of 5-10% increase in plasma volume, the levels would fall accordingly. But the results would come back to normal in subsequent tests when the hydration is normal. So follow up tests need to be taken.

Dr. Saha and 2 other Health Specialists are ready to help you
Customer: replied 4 years ago.

I am recovering from life threatening Anemia 8 months ago and I want to better understand by how much these fluctuations in hydration can potentially affect my blood counts so I can better interpret whether they actually worsen or improve. Or if certain changes could be attributed to hydration.


I need to drink a lot of water to stay hydrated because I lose so much from sweat during exercise. My weight regularly fluctuates by as much as 4 pounds in a day from water weight.


By how much can overhydration or dehydration affect hematocrit, hemoglobin, and RBC? I am asking for ranges. Would the recent variation be within these ranges or could they indicate that my total blood count has dropped since May?



How is your body weight?
Customer: replied 4 years ago.

I am about 20 pounds overweight with a very muscular build.

Customer: replied 4 years ago.

About 240 pounds, male, with very muscular build. About 20 pounds overweight.

If you notice an increase of 4 lbs in your weight from water retention or overhydration, this should be calculated with your normal weight.

Some of it would be collected in the extracellular space & some in the blood.

If we take your normal weight as 240 lbs, then an increase of 4 lbs, would be distributed accordingly.

So you can expect a similar decrease of hemoglobin & hematocrit by the range of not more than 5-10%.
Dr. Saha and 2 other Health Specialists are ready to help you