For patients with MGUS, the size of the monoclonal protein, type of monoclonal protein, sFLC ratio, as well as the proportion of aberrant plasma cells within the bone marrow are helpful in identifying patients who are at increased risk of progression . These International Myeloma Working Group (IMWG) guidelines  recommend that patients with MGUS should be risk stratified at diagnosis, to optimise counselling and follow-up, using a model incorporating the following risk factors: 1) serum monoclonal immunoglobulin ≥15 g/L; 2) serum monoclonal immunoglobulin type (IgA or IgM); and 3) abnormal κ/λ sFLC ratio (Table 25.3 and Chapter 13). For patients with low-risk MGUS, a baseline bone marrow examination or skeletal radiography is not routinely indicated. For patients with intermediate- and high-risk MGUS a bone marrow aspirate and biopsy should be carried out at baseline to rule out any underlying plasma cell malignancy .
|MGUS risk group||Criteria||Absolute risk* (%)||Recommended follow-up|
|Low||No risk factors present||2||6 months initially, and if stable, follow up every 2 - 3 years or when symptoms suggest a plasma cell malignancy|
|Low-intermediate||Any one risk factor present||10||6 months initially, then annually and upon any change in the patient's clinical condition|
|High-intermediate||Any two risk factors present||18|
|High||All three risk factors present||27|
|*of progression at 20 years accounting for death as a competing risk. Risk factors are defined as serum monoclonal immunoglobulin ≥15 g/L, serum monoclonal immunoglobulin type (IgA or IgM) and an abnormal sFLC κ/λ ratio.|
Table 25.3. Summary of MGUS risk groups and recommended follow-up.
For patients with SMM, the guidelines  recommend SPE plus electrophoresis of a 24-hour urine, to confirm the diagnosis and full blood cell count plus serum calcium and creatinine measurements to rule out MM, at baseline and after 2 - 3 months. Baseline sFLC measurements are required for risk stratification and a baseline bone marrow biopsy and skeletal survey are mandatory. If the results are stable, the studies should be repeated every 4 - 6 months for the first year, and then, if remaining stable, the follow-up period can be lengthened to 6 - 12 months .