I found this online today here, ncbi.nlm.nih.gov/books/NBK5... It describes new methods of diagnosing PA. It looks interesting.
Alternative and new approaches to the diagnosis of PA are under evaluation. One of these is a newer propriety cobalamin absorption test, which has its basis in measuring the change in holoTC following oral ingestion of non-radiolabeled cobalamin. Another approach has been described using accelerator mass spectrometry to quantify 14C in the blood following an orally administered dose of [14C]-cyanocobalamin.[11] One may empirically administer vitamin B12 intramuscularly and assess the response if cobalamin deficiency is suspected. Most patients will feel clinically better within 24 hours. Additionally, marked reticulocytosis will appear within 5 to 7 days.