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.
The SAP scan can show the amount and location of amyloid within the body without the need for invasive biopsies. A small amount of SAP is tagged with a radioactive iodine tracer and is injected into a vein. The tagged SAP then binds to amyloid deposits within the organs of the body. A scan is then performed 6 – 24 hours later to show these deposits and the amount and location of amyloid within the body.
Doctors at the National Amyloidosis Centre have performed many thousands of SAP scans since the test was devised in 1987. Through these scans, doctors have gathered a large amount of information that will continue to guide treatment decisions and improve understanding of AL amyloidosis.