Diagnosing amyloidosis typically requires a combination of blood tests, tissue biopsy with specialized staining, and imaging, followed by tests to identify the exact type of amyloid protein involved. Because amyloid deposits can affect the heart, kidneys, liver, and nerves, the diagnostic process often depends on which organs are showing symptoms and which type of amyloidosis is suspected.
Blood and Urine Tests as a First Step
When doctors suspect amyloidosis, they usually start with blood and urine screening to look for abnormal proteins. For AL amyloidosis, the most common form requiring treatment, the key screening tool is the serum free light chain assay. This test measures two types of antibody fragments (kappa and lambda light chains) floating in your blood and calculates their ratio. A normal ratio falls between 0.26 and 1.65. When the ratio drops below 0.26 or rises above 1.65, it strongly suggests a problem with plasma cells producing too much of one type, which is what drives AL amyloidosis.
Doctors also use a test called immunofixation electrophoresis (IFE) to detect monoclonal proteins in blood and urine. These are identical copies of an abnormal protein churned out by a single clone of plasma cells. However, IFE can miss cases where the abnormal protein level is low. In one study of 60 newly diagnosed AL amyloidosis patients, more than a third had undetectable monoclonal protein on one common testing platform. When those same samples were retested on a different, more sensitive system, half turned positive. This is why doctors often run multiple overlapping tests rather than relying on a single result.
Tissue Biopsy and Congo Red Staining
A definitive amyloidosis diagnosis requires proof that amyloid protein has actually deposited in tissue. The gold standard is a biopsy stained with a dye called Congo red. Under regular light, Congo red turns amyloid deposits a salmon-pink color. The real confirmation comes when the pathologist switches to polarized light microscopy: amyloid fibrils stained with Congo red produce a characteristic green color visible between crossed polarizing filters. This green birefringence is considered diagnostic of amyloid and is reported as the definitive evidence.
The simplest starting biopsy is a fat pad aspiration, where a needle draws a small sample of fat from under the skin of the abdomen. It’s quick, minimally invasive, and has 100% specificity and positive predictive value, meaning a positive result reliably confirms amyloid. The catch is sensitivity. Fat pad biopsy picks up about 84% of AL amyloidosis cases, but only about 15% of wild-type ATTR amyloidosis cases (the age-related form affecting the heart). Roughly 11% of specimens come back as inadequate for reading. If the fat pad biopsy is negative but suspicion remains high, a biopsy of the affected organ, such as the heart, kidney, or liver, is the next step.
Identifying the Amyloid Type
Confirming that amyloid is present is only half the job. There are over 30 different proteins that can misfold into amyloid fibrils, and each type requires a completely different treatment approach. AL amyloidosis involves antibody light chains and is treated with chemotherapy. ATTR amyloidosis involves a liver protein called transthyretin and is treated with stabilizer drugs or gene-silencing therapies. Getting the type wrong can be dangerous.
The most reliable method for typing is mass spectrometry. In this technique, a pathologist identifies the amyloid deposit under the microscope, carefully cuts it out of the tissue slide, and analyzes its protein composition. Mass spectrometry can distinguish all major amyloid types with 100% specificity. It’s especially useful for ambiguous cases. In one reported case where standard methods labeled the amyloid type as “indeterminate,” mass spectrometry was able to identify it as AL amyloidosis based on the ratio of lambda to kappa light chain fragments in the tissue.
Not all centers have mass spectrometry available, so some rely on immunohistochemistry, which uses antibodies to identify the amyloid protein in the tissue. This works well in some cases but can give unclear or incorrect results, particularly when tissue quality is poor or multiple proteins are present. When immunohistochemistry results are inconclusive, samples are typically sent to a specialized reference lab for mass spectrometry.
Cardiac Imaging for Heart Involvement
Because the heart is one of the most commonly affected organs, cardiac imaging plays a major role in diagnosis and staging. Two imaging techniques are particularly important.
Nuclear Bone Tracer Scan
A technetium pyrophosphate (PYP) scan uses a radioactive tracer originally designed for bone imaging. The tracer has a strong affinity for transthyretin amyloid deposits in the heart. Results are graded on a 0 to 3 scale. Grade 0 means no heart uptake (normal). Grade 1 means some heart uptake but less than the ribs. Grade 2 means heart uptake equal to the ribs. Grade 3 means heart uptake exceeds rib uptake, with the ribs barely visible.
A grade 2 or 3 result, combined with blood tests that rule out AL amyloidosis, can confirm ATTR cardiac amyloidosis without a heart biopsy. This was a significant advance because it spared many patients, particularly older adults with the wild-type form, from an invasive cardiac biopsy. A grade 1 result is less definitive and usually requires further workup.
Cardiac MRI
Cardiac MRI with a contrast agent called gadolinium can reveal patterns of amyloid infiltration in the heart muscle. When gadolinium lingers in tissue after injection (called late gadolinium enhancement), it signals damage or abnormal deposits. In AL amyloidosis, a pattern of enhancement along the inner layer of the heart wall (subendocardial) is considered typical, while ATTR amyloidosis can show different enhancement patterns. Cardiac MRI helps evaluate how much of the heart is involved and can raise suspicion of amyloidosis even before a biopsy is done.
Genetic Testing for Hereditary ATTR
Once ATTR amyloidosis is confirmed, genetic testing determines whether it’s hereditary (caused by a mutation in the TTR gene) or wild-type (age-related, with no mutation). This distinction matters for treatment decisions and for screening family members. Sequence analysis of the TTR gene detects 100% of known disease-causing mutations.
The most common mutation worldwide is p.Val50Met, which predominates in Portugal, Sweden, and Japan and tends to cause nerve-predominant disease. The most common mutation in people of African descent is p.Val142Ile, carried by 3% to 4% of African Americans. Most people with this variant develop heart-predominant amyloidosis later in life. Over 130 different TTR mutations have been identified, so full gene sequencing is preferred over testing for a single variant unless the family mutation is already known.
Staging After Diagnosis
Once the type of amyloidosis is confirmed, doctors assess how much organ damage has occurred. For AL amyloidosis with heart involvement, staging relies on blood markers of heart stress and damage. The widely used Mayo 2012 staging system assigns points based on three values: a heart strain marker called NT-proBNP (threshold of 1,800 pg/mL), a heart injury marker called high-sensitivity troponin T (threshold of 40 ng/L), and the difference between involved and uninvolved free light chains in the blood (threshold of 180 mg/L). Patients are grouped into stages I through IV based on how many thresholds are exceeded, with higher stages indicating more advanced cardiac involvement and a more urgent need for treatment.
A European modification of an earlier staging model uses slightly different cutoffs for troponin (50 ng/L) and a lower NT-proBNP threshold (332 ng/L), with an additional subdivision at very high NT-proBNP levels (8,500 ng/L) to identify the highest-risk patients. These staging systems help guide how aggressively treatment should be pursued and provide a baseline for tracking response.