Since you mention molecular biology, I am assuming that the "test" being ordered by the physician relates to DNA or RNA separation. Having worked as a Medical Technologist in a lab a number of years ago, I can tell you that DNA & RNA proteins are often separated through gel electrophoresis, one of the main tools of a molecular biologist. The proteins are separated on the basis of size by running a DNA sample through agarose gel using an electrical field. We refer to the "wells" in the gel as "lanes." Typically, you might have a result with Lane 1 as a positive control, Lane 2 as a negative control, and Lane 3 as the sample. The control lanes are used to compare & contrast your sample to the control lane to help identify characteristics.
I am not sure how to address the issue of diagnosis. What was the molecular biology data given to you? The control lane would certainly help to identify the sample, but you do not mention a specific test or data.
Yes, a physician can proceed with diagnosis of a disease based on molecular biology data. It would have been easier to explain if you had shared the data with us.
Molecular Biology techniques like polymerase chain reaction (PCR) is widely used for diagnostic purposes. Pathogen specific primers or disease causing gene specific primers are used for the amplification of a DNA fragment. The DNA fragment of expected size amplified from a clinical sample is indicative of the presence of the pathogen/ gene in the patient.
PCR reactions are carried out with the clinical sample collected. The presence or absence of the amplified product is checked by loading the reaction mixtures on an agarose gel along with a positive and a negative control. The positive control will be a known sample containing the DNA fragment and the negative control will be the one which does not contain the pathogenic agent. These controls are included in the gel in order to ensure that the experiment has worked the way it should and there are no false positive results generated due to experimental errors.