![]() ![]() MGUS that presents with no quantifiable M spike but with an IFE abnormality can be termed IFE MGUS. Although not quantifiable and more difficult to detect, subtle abnormalities such as fuzzy γ bands can reflect serious diseases. These small monoclonal proteins are therefore often not quantitated and described only as small abnormalities. Quantitating an M spike in which the M protein may be less than 25% of the protein is inaccurate and may be misleading. If a small M protein migrates within the β or α fractions or within a large polyclonal background, quantitation of the M protein will include substantial amounts of normal proteins. The quantitation of M proteins is a different process from the qualitative detection of M proteins. 10- 13 The limit of detection of M proteins with SPEP is 0.02 to 0.04 g/dL if they migrate in the γ fraction. If the concentration of the M protein is small or if the M protein migrates in the β or α fractions, the M protein becomes more challenging to detect. SPEP is also a method to quantitate and monitor the M protein the M protein fraction is described as an M spike. Serum protein electrophoresis (SPEP) is often used as the screening test for detecting monoclonal gammopathies 7- 9 and will trigger IFE confirmation. To diagnose MGUS, the presence of a monoclonal immunoglobulin must be established by means of immunofixation electrophoresis (IFE). 4, 5 A serum monoclonal protein concentration of at least 1.5 g/dL (15 g/L) is one of the risk factors for progression. The overwhelming majority of multiple myeloma cases are preceded by MGUS, 3 and the rate of progression of MGUS to multiple myeloma or a related malignant condition is 1% per year. 2 Although asymptomatic, a diagnosis of MGUS has long-term implications for the patient. 1 If light-chain MGUS is included, the respective numbers are 4.2% and 6.6%. MGUS has a prevalence of more than 3% in the population of those aged 50 years or older and the prevalence increases to 5% or higher in those older than 70 years. Monoclonal gammopathy of undetermined significance (MGUS) is the most common plasma cell proliferative disorder. ![]()
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