source: Myeloma UK summary/abstract:
Serum amyloid P component (SAP) is a normal protein found in the blood that binds to amyloid deposits. In healthy people, there are very small amounts of SAP and this is only present in the bloodstream. In AL amyloidosis patients, in addition to the small quantities of SAP in the blood, there are large quantities of SAP coating the amyloid deposits in the affected organs. The SAP scan is available at the NHS National Amyloidosis Centre, London, and is performed routinely in most patients who are referred there for evaluation of AL amyloidosis.
How Does the SAP Scan Work?
The SAP scan uses the SAP coating on amyloid deposits to determine where and how much amyloid has been deposited in the organs. A small amount of SAP is tagged with a radioactive iodine tracer. This tracer emits a small radioactive signal which can be detected outside the body with a piece of equipment called a gamma camera. The tagged SAP is injected into a patient and binds to amyloid deposits within the organs of the body.