Hydroxyurea can affect the results of blood tests that measure urea, so a reading may not show the true level. If you are taking hydroxyurea and need a urea test, tell the doctor or the lab staff beforehand so they can read the result with this in mind.
These medicines are often taken together with some care. Your doctor may change a dose, space them apart or check on you more often. Make sure your doctor and pharmacist know you take both.