What would abnormal vitamin a serum blood test mean ?

A few things...: "abnormal" on a blood test usually means the result is higher or lower than what is found in 95% of the normal people in the community. For vitamin a, one can ask his doctor why the test was done (it is not a routine test that everyone gets). A very high result means a patient is eating too much vitamin a (from foods or supplements), and low means he is not eating or absorbing enough vitamin a.