20 CFR §404.1519a

1. (a)General. If we cannot get the information we need from your medical sources, we may decide to purchase a consultative examination. See § 404.1512 for the procedures we will follow to obtain evidence from your medical sources and § 404.1520b for how we consider evidence. Before purchasing a consultative examination, we will consider not only existing medical reports, but also the disability interview form containing your allegations as well as other pertinent evidence in your file.
2. (b)Situations that may require a consultative examination. We may purchase a consultative examination to try to resolve an inconsistency in the evidence, or when the evidence as a whole is insufficient to allow us to make a determination or decision on your claim. Some examples of when we might purchase a consultative examination to secure needed medical evidence, such as clinical findings, laboratory tests, a diagnosis, or prognosis, include but are not limited to:
   1. (1)The additional evidence needed is not contained in the records of your medical sources;
   2. (2)The evidence that may have been available from your treating or other medical sources cannot be obtained for reasons beyond your control, such as death or noncooperation of a medical source;
   3. (3)Highly technical or specialized medical evidence that we need is not available from your treating or other medical sources; or
   4. (4)There is an indication of a change in your condition that is likely to affect your ability to work, but the current severity of your impairment is not established.