It's likely some lab mistake, or a combination of that and dehydration. It seems like in my case, dehydration can easily make a %point or more difference easily. I have apnea also, and my HCT tends to climb up to about 54% about every 4-5 months, but staying hydrated, donating about every 4 months to 5 months, and using my CPap keeps it down under the magic number of 54% pretty regularly. I don't mind donating a couple times a year of so, either. But recently mine climbed up faster than usual, in about 3 1/2 months. I have been having some new sleep issues and seem to finally have them resolved. I have a hematologist that follows, and she doesn't get worried at all about HCT at 54%, but doesn't like it to ge much higher. she is also ok with me donating every 3 months if needed. She watches my iron and does counsel me on diet so my iron doesn't get depleted. Good news, is I get to eat lots of red meat if I have to donate more often. She doesn't give me iron supplements because she believes it will further aggravate the HCT production. If your iron swings down, bring it back gradually with diet.