The answer is there are several reasons. Laboratory or genetic tests can be erroneous; blood samples can be mixed or lab technicians can get sloppy and make mistakes or not have adequate training to do the tests. Also, a family and personal history are extremely important, as is a complete physical examination.
Some laboratories are very reliable,while others are known to make frequent errors. Now that many new genes are being discovered, some physicians simply order blood work, send it to a lab for genetic testing and then when the results come in send the patient or parents to a genetic counselor. I am always amazed and sad that any physician would base a diagnosis completely on a laboratory test. As medical students are being taught medicine with the use of computers and not good bedside and clinic teaching, as I had and though some genetic counselors have Ph.Ds, others have much less training. I would assume all physicians would want to sit down with their patient or parents and go over the tests results themselves. However, if the physician does not have adequate training or experience with a particular disorder, this is an easy way to get out of answering questions.
The most important thing in diagnosing a patient with muscle weakness is still a complete physical examination and a family history and always questions about any anesthetic problems. The blood test CPK (CK in Europe) should be ordered on the patient and often the mother. The next extremely important step is to obtain a muscle biopsy under a local anesthetic. A general anesthetic could cause problems with Malignant Hyperthermia. A neuromuscular specialist should look at the biopsy and not leave the diagnosis to a pathologist who may not have had training in reading muscle biopsies. If there is a question, a second opinion should always be obtained.
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Article last time updated on 17.11.2016.