I am pretty sure I an low on iron as I have heavy periods and a short menstrual cycle. I am constantly tired although I get enough sleep. My GP has said I should go for blood tests but they do not take blood at the GP surgery, so I have to travel to my local hospital during my working day, miles away from where I work to get the blood Sample taken. So I have to leave this for a week because I just can't afford to take more time off work. It's fine, I'll go and get it done within the next week burt I am impatient and I have some iron supplements that I want to start taking straight away. So my question is this: will taking iron supplement for a week mask the blood test results? The range of tests are 'FBC & Diff', 'iron levels', 'electrolytes', 'liver function tests', 'thyroid function tests'.