Not necessarily. Medicine is not an exact science; doctors are not required to be right every time they make a diagnosis. A misdiagnosis can be arrived at through standard tests, even when the tests are performed accurately or evaluated by a skilled doctor with the utmost care.
That said, a misdiagnosis may be malpractice if the doctor fails to get a medical history, order the appropriate test for the illness, or recognize the symptoms of the illness. Yet there is no basis for a malpractice claim if there is no injury, loss or damage as a result of the misdiagnosis and consequent treatment, on the theory that you are no worse off than you were before.
If you have sustained losses due to the negligence of a medical professional, you should seek the advice of a medical malpractice attorney, and do so quickly to ensure your rights are preserved.