If you are dehydrated for any reason, dialysis or otherwise, it will make your hemoglobin read deceptively high because there will be a greater ratio of hemoglobin to fluid. The concentration of hemoglobin reads higher, but your actual hemoglobin amount may be fine. The reading that they take is your concentration of hemoglobin, not the actual amount. That's why the fix may be as easy as drinking up! Sorry, not a medical pro, so explanation may be muddled.... Good luck with your appointment.
When I come in after a weekend and the first thing they do is take a lab draw then my fluid is really high. That should make my hemoglobin deluded? So my actual hemoglobin is probably higher than I get credit for.