How is AL amyloidosis most commonly diagnosed?

AL amyloidosis, also known as primary amyloidosis, is primarily diagnosed through a combination of tissue sampling and laboratory tests that confirm the presence of amyloid deposits. The most common sites for obtaining a diagnosis include the abdominal fat pad and the bone marrow.

The abdominal fat pad aspirate is particularly useful because it is minimally invasive, and the fat tissue can often harbor amyloid deposits that are readily identifiable via Congo red staining under polarized light, revealing apple-green birefringence. Additionally, a bone marrow biopsy can aid in diagnosing AL amyloidosis by identifying the presence of monoclonal plasma cells, which are typically elevated in this condition. The relationship of these two procedures helps to confirm the diagnosis by providing both the presence of amyloid and the underlying plasma cell dyscrasia.

While the other diagnostic methods mentioned may provide useful information in the assessment of a patient suspected of having AL amyloidosis, they are not the mainstay for diagnosis. A skin biopsy might reveal amyloid deposits, but this is less common and not as definitive as examining the abdominal fat pad and bone marrow. Urine tests can show light chain proteins, but these are more related to monitoring rather than establishing the diagnosis. Imaging studies might help assess organ involvement but are