fasting from water as well as food
Many people treat a fasting blood test like a Ramadan fast and skip water too. That dehydrates you, makes the vein harder to find and concentrates the sample enough to distort results. Plain water is allowed and encouraged right up to the draw — only food, caffeine and sugary drinks break the fast.
taking hormone tests at random times
An afternoon cortisol reading or a day-14 FSH draw produces numbers that look meaningful and are not. Hormones follow daily and monthly rhythms, so book the draw for the hour and cycle day your doctor specifies. Getting the timing right is precisely what home collection makes easy — use that advantage.
switching laboratories between follow-up tests
Reference ranges and assay methods differ between labs, so a borderline thyroid or cholesterol value retested somewhere new may move for reasons that have nothing to do with your health. For trend-watching, stick with one laboratory — rebooking the same vendor keeps your numbers comparable year to year.