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.
using an IgG panel to rule out a real allergy
If you suspect a true allergy — swelling, hives, breathing trouble — an IgG food intolerance panel is the wrong tool and a clear result from one proves nothing. True allergy is IgE-mediated and needs proper testing and a doctor. Confusing the two can leave a dangerous allergy undetected.
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.