Welcome to the Health Care Magic
Time, weight, diet, drugs, stress
and so on are some factors that can influence the results..
Human errors like sample quantity, mislabelling and so on are also possible.
When in doubt as in this situation, the only option is to go for the test for the third time – in a standard Laboratory. After all, it is your health that needs attention / and many treatment decisions are based on the results of the tests.