Nattokinase works very well, but the best thing you can do is stay hydrated. This can have a 3-5pt sway in numbers for RBC and HCT. I always knew this, but confirmed it the other week when I went in for my 6 month labs. Had an early morning lab and drank a couple cups of coffee, no water as I was in a rush and got a call about my RBC and HCT being elevated. Mind you, I am in elevation so they will never bat an eye at this unless it is abnormal. So they said my HCT was at 55.8 and I am always around 50-51. Doc said, don't worry about it since it was one test, but I told him I knew why and wanted to retest. Scheduled a later in the day test, hydrated properly and resulted in a 49.7.
It's becoming a bit more known that there is an unnecessary concern about HCT ranges and a couple of podcasts and videos from some prominent HCT docs stating that unless it is nearing 60s, there is no risk of cardio or stroke issues. Not that you wouldn't feel like **** with it that high first.