Laboratory tests are done at baseline and during the course of treatment. With the referral letter it may be helpful to organise the baseline investigations which are a fasting cholesterol and triglyceride test, liver function tests and a pregnancy test for females. Oral isotretinoin may cause an increase in blood lipids. After the patient has had 4–8 weeks therapy, the laboratory investigations are repeated and compared to baseline. If the tests are normal they may be repeated at the end of treatment, however if there are any abnormalities they will need repeating more regularly with or without lowering of the daily dose.