A strongly positive bone scintigraphy scan is diagnostic of transthyretin cardiac amyloidosis only when a monoclonal protein has been excluded. Light-chain amyloid can take up bone tracer, and missing it delays chemotherapy in a disease where weeks matter.
Send serum free light chains with the ratio, and serum and urine immunofixation, at the same time as the scan request.
- Order serum free light chains and serum and urine immunofixation alongside any bone scan for suspected amyloid.
- Refer urgently to haematology if a monoclonal protein is found, whatever the scan shows.
- Remember that kidney impairment raises both free light chains; the ratio is more useful than the absolute values.
- Consider genetic testing once transthyretin amyloid is confirmed, to separate hereditary from wild-type disease.
Why it matters
Light-chain amyloid is the treatable emergency hidden inside the amyloid work-up.
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