Several studies have evaluated the prognostic impact of an increasing monoclonal protein concentration during follow-up on risk of SMM progression. Many , but not all studies , have reported a higher risk in patients who demonstrate a progressive rise in serum monoclonal protein. For example, Fernandez de Larrea et al.  studied 207 SMM patients, and defined an "evolving" monoclonal protein type as either a 10% increase within 6 months of diagnosis (for patients with an initial monoclonal protein ≥30 g/L) or a progressive increase in consecutive annual measurements during a period of 3 years (for patients with an initial monoclonal protein <30g/L). A quarter of patients displayed an evolving type, and this was associated with significantly shorter median time to progression (19.4 vs 3 years, p<0.001). The authors concluded that SMM should be routinely monitored for an evolving type during follow-up.
International guidelines recommend that serum protein electrophoresis and 24-hour urine electrophoresis are performed at SMM diagnosis and at 2 - 3 months. If the results are stable, the patient should be followed every 4-6 months for 1 year and, if stable, every 6 - 12 months (Section 25.3.2). Whilst there are no recommendations for the frequency of sFLC analysis during follow-up, in a recent review article, Rajkumar  suggested that sFLCs should be evaluated every 3 - 4 months.