Hair Analysis/Blood Work-What if results Differ?

Was just wondering why if one has a blood test and a hair analysis why these two tests would come back saying the opposite?

For example, why it would show high magnesium or calcium in the hair analysis and the opposite in the blood test (low magnesium or calcium)???

It is so confusing. How do I know then if I am high or low in any mineral if the two tests show the opposite?

Which one is more trusting? or does it have to do w/ absorption? Very confused please clarify if can.