A blood test once a month usually does not cause anemia.
The average weight of normal adult male contains (80~85) ml/kg of blood, while the average weight of adult female is about 70 ml/kg, and the volume of blood in one blood test is about 2~3 ml. A blood test once a month generally will not cause anemia symptoms because the volume of blood extracted is small, and it does not have much effect on the human body in general.
If anemia is found in the blood test, it may be due to iron deficiency anemia, megaloblastic anemia or aplastic anemia, which need to be combined with bone marrow biopsy to confirm the diagnosis. It is recommended to consult the doctor as soon as possible to find out the cause of the disease and to avoid delaying the condition.