Can morning after pill be detected by an anemy blood test?

No : The morning after birth control pill cannot be detected in any blood test.

Tests are specific: An anemia test is specific. It will look at the amount of blood you have and sometimes the size of the blood cell & amount of oxygen carrying hemoglobin. These tests require specific technical equipment and a quantity of blood. They don't look at other things that would use more blood, need other equipment or be technically difficult.(they couldn't detect this)