Because the symptoms are non-specific, it is possible for the diagnosis to be delayed by more than a year from the onset of symptoms. Diagnosis of AL amyloidosis may involve several tests, including blood tests, urine tests, imaging and (required in all cases) a biopsy to identify light chain amyloid deposits. Biopsies and bone marrow tests are necessary to confirm the diagnosis of amyloidosis and determine what type of amyloidosis a patient has. Blood and urine tests are useful for establishing that amyloid is present, while specialised testing of organs may be required to determine the extent of damage to the organs affected by the disease. Early diagnosis of AL amyloidosis is paramount because early treatment may prevent or mitigate further organ damage.
This are the most common test in the diagnosis of AL amyloidosis:
Blood and urine tests
There are several kinds of blood and urine tests that can be performed to aid the diagnosis of amyloidosis and determine treatment response once the
diagnosis has been established. They are also helpful in identifying which organs are affected by the condition and to investigate the severity of organ damage. Examples of such tests are:
- Assessing protein levels in the urine: samples are collected in a 24-hour period to determine the protein levels in the patient’s urine. Excess protein in the urine (proteinuria) can indicate that the kidneys are affected by the disease, which can lead to kidney damage and, ultimately, kidney failure.
- Assessing ALP (alkaline phosphatase) levels in blood: in the blood may be assessed. ALP is an enzyme present throughout the body, which is needed for the breakdown of proteins, an important part of healthy cell and tissue function. Abnormal ALP levels most often indicate a liver involvement.
- Assessing heart function (biomarker): A biomarker is a biological feature of the body that can be measured by looking at the presence (or absence) and rate of a certain Blood tests can be used to assess the function of the heart. Examples of these biomarker tests are: troponin T, troponin I, NT-proBNP (which stands for N-terminal pro-brain natriuretic peptide) and BNP (brain natriuretic peptide). These markers are diagnostic tools for cardiac involvement with high sensitivity and can detect early disease (without symptoms).
- Testing abnormal antibody (immunoglobulin) in blood: Such as the serum free light chain (FLC) test. This test allows the assessment of kappa and lambda light chain levels that make up the abnormal amyloid fibrils.
- Immunofixation and electrophoresis: This test can be done on blood or urine samples. It allows the measurement of abnormal monoclonal proteins, M proteins.
The collection of urine samples is a straightforward process, although somewhat cumbersome in the case of 24-hour urine samples. For a test using blood, the nurse will insert a needle into a vein in the arm and extract several vials of blood. The amount withdrawn depends on the laboratory technology and protocol applied: it is usually between 30ml and 50ml distributed across several vials.
Echocardiogram and imaging
An echocardiogram (or “echo”) is a type of ultrasound scan used to look at the heart and nearby blood vessels. Echocardiograms use a device that emits ultrasound and measures its reflection from the organs in the body. The doctor or technician applies a gliding lubricant to the area where the scan is performed, and then carefully moves the ultrasound device around the skin. Amyloid deposits in the heart cannot be visualised with an echocardiogram but it can detect thickened cardiac walls that also do not relax as should be.
Alternatively, magnetic resonance imaging (MRI) can be useful for visualising certain aspects that are very specific to amyloid deposits. The reflections from the internal organs are processed by a computer to generate an image. The patient may be administered a contrast agent and is then placed in an MRI machine. The machine emits magnetic rays at high speed that are reflected from the cells in the body. An elaborated computer model is used to measure these reflected waves and to construct a three-dimensional image of the internal organs and their possible visible changes. Some patients may find the MRI examination uncomfortable as they have to spend a relatively long time not moving and confined to a narrow tube inside the MRI device. It is also a noisy examination as the device uses large magnets rotating at high speeds. Both of these imaging techniques are relatively easy and cause no pain.
Another important imaging technique is referred to as an SAP scan. SAP stands for serum amyloid P component. During this test, the patient receives an injection of this component together with a labelling agent. The amyloid deposits can then be visualised with a scanning method, thus determining the size and location of the deposits. This test is only available in few countries such as the Netherlands and the UK, so it is not mandatory for a complete clinical assessment
Tissue biopsies
A biopsy is taking small sample of tissue. This is often taken under the skin of the periumbilical (around your belly button) area (abdominal fat biopsy or fat pad aspiration). Abdominal fat biopsies are relatively easy and not particularly painful. Alternatively, a biopsy can also be taken from the organ affected by amyloid deposits. However, biopsies from other internal organs can be complicated and painful as well, and so this diagnostic method should be used sparingly. Another possible valid approach is to obtain a small salivary gland biopsy.
During biopsy, a long needle is inserted into the organ to be examined and a small amount of tissue is extracted for the test. This may be painful or uncomfortable. The tissue samples are then stained with a dye called “Congo red stain” and examined under a microscope. Congo red reacts with the amyloid proteins for visualisation. Once amyloid fibrils are detected, to distinguish between the different form of amyloidosis, a typing of amyloid protein must be performed. There are two main tests used to characterise amyloid deposits: immunoelectron microscopy and mass spectrometry.
Bone marrow tests
Bone marrow samples are used to find the abnormal cells producing the free light chains. There are two types of bone marrow samples: a bone marrow aspirate (BMA) involves fluid aspiration from the bone marrow, while a bone marrow biopsy (BMB) removes a small piece of bone marrow tissue. However, bone marrow aspirates are not advised in AL amyloidosis because an aspirate cannot be examined for amyloid presence. During this procedure, which can be done on an outpatient basis, a long needle is inserted into one of your larger bones, usually the pelvis, and a small amount of bone marrow is obtained. Bone marrow biopsies can be particularly challenging and painful. Local anaesthesia will be performed during the procedure to numb the area of needle insertion. In some cases, you may receive sedation for the time of the test to reduce your pain. You may also experience pain at the biopsy site for several days after the procedure. In the laboratory, Congo red staining can only be performed on bone marrow biopsy samples to determine if amyloid is present.
Specialised testing of affected organs
If signs of organ involvement are detected throughout initial testing (for example, by looking at blood and urine samples), doctors may decide to carry out biopsies taken from these organs or perform other diagnostic methods (such as an echocardiogram to investigate heart health) to determine the extent and severity of organ damage.
Prognosis
Prognosis refers to the forecast or anticipated course of a medical condition. The prognosis of AL amyloidosis is highly dependent on a patient’s response to treatment and the extent of organ damage at diagnosis. Specifically, the extent and severity of heart involvement are considered a significant determinant of the prognosis of AL amyloidosis. When significant damage to the heart is already present at the point of diagnosis, patients generally have a poor prognostic outlook (with a high risk of death within a few months). Additionally, life expectancy varies according to the stage of the disease. Early diagnosis is therefore extremely important in order to achieve the best possible treatment outcome and prognosis. Prolonged survival is possible when treatment commences early in the course of disease and the patient responds well to treatment. For all these reasons the current median survival varies a lot between individual patients, from three months to several years, and this may evolve rapidly with the discovery of new treatments.
