Yes, your blood counts can be affected by many things, dehydration, exercise, hormones etc. As Katie said, they give a range as the body fluctuates to accommodate all the processes going on. These tests are worked out based on mass averages, some people will always sit at the ends of the scales (that's how averages work).
The reassuring thing, is your body is doing as it should and managing within these normal levels. On occasions it may rise out of these levels, but it doesn't mean you have problems, it only begins to raise flags when levels are persistently abnormal, and rising not reducing. Luckily yours are perfect.
I did lots of googling about it and it all seems to says exactly as you do.
I did read an interesting study that showed a 10-20% increase in bilirubin levels after fasting. I guess there are many things that impact it like you say.
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