Deodorant before a mammogram
A mammogram is an x-ray picture of the breast. Many deodorants contain aluminum, which on mammography looks similar to breast calcifications and could be read as a false positive test.

Getting thirsty before a urine test
If you are going for a urine test, it is best not to get dehydrated before your appointment. If you exercise, make sure you drink plenty of water afterward. Avoid episodes of major dehydration that can significantly alter a urinalysis.
Alcohol before a cholesterol test
Abstain from alcohol for 24 hours prior to a cholesterol test. Alcohol is likely to alter your cholesterol profile. Also, avoid sweets, high-fat foods and overeating before the test.
These, in large quantities can cause fluctuations in your cholesterol level.

Getting a manicure or pedicure
Before visiting a dermatologist, it is not advisable to get manicure or pedicure because dermatologists look at your whole body, including your nails, so you should keep them polish-free. Wearing nail polish or acrylic nails may hide issues such as fungus, subtle clues in your nails which can indicate bigger health problems such as anemia, diabetes, and even heart ailments.

Eating before a diabetes test
When going for a fasting blood glucose test (used to diagnose diabetes), you cannot eat or drink anything but water for eight hours before your test. You may want to schedule a fasting glucose test first thing in the morning so you do not have to fast during the day.
Also iron blood tests to detect anaemia are usually taken in the morning before you eat anything. You should also avoid taking iron pills or tablets for 24 hours before your test.