About 10-15% of patients with AL amyloidosis have only minimally abnormal FLC, so FLC cannot be used for accurate monitoring. A measurable M-protein (also known as paraprotein), defined as >5g/l, is useful for monitoring the haematological response to chemotherapy in these patients.
1-2% of patients with AL amyloidosis lack a measurable serum or urine marker to monitor response at present. Ongoing studies are evaluating a new method called high sensitivity flow cytometry that may have a role.