It's me again..
How soon after you took your dose can affect levels. What you ate around the time you took the dose can affect levels. Certain drugs and even foods can influence metabolism and affect levels. Poor liver function can affect levels. Variation between laboratories running the test and individuals performing the test can chage results even when the levels are in fact consistent.
Plus a number of other factors. Really, the difference between 150 and 200 is well withen normal analytucal errot so that isn't a big problem. As far as 600, that's only one result, I wou look don't worry to much.
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Jennifer