Stop carbimazole.. Stop carbimazole since it can interfere with radioactive iodine uptake calculated on thyroid scan. Some institutions vary as to number of days to stop carbimazole before the scan. Some institutions say stop 48 hours before. Some say 7 days. Four or fives days should be sufficient but you could stop carbimazole for 7 days to be on safe side. Check with nuclear medicine dept. ; your doctor.