[Beacon Staff]

–► Criteria for an MGUS diagnosis

by Beacon Staff on Sat Nov 01, 2014 10:00 pm

Generally speaking, a diagnosis of MGUS (monoclonal gammopathy of undetermined sig­nifi­cance) is called for when there are signs of abnormal (clonal) plasma cells in a patient's body, but the cells are not so numerous that the patient meets the criteria for a smoldering multiple myeloma diagnosis, or the criteria for a symptomatic (active) multiple myeloma diagnosis.

Usually the signs of abnormal plasma cells being present are lab test results that show one or more of the following:

1. An M-spike (monoclonal protein, paraprotein, or abnormal protein) in the blood
2. Monoclonal protein in the urine
3. Elevated kappa or lambda serum free light chain levels, accompanied by an abnormal kappa-lambda ratio.

A patient's M-spike is reported in their serum protein electrophoresis (SPEP) results. Urine monoclonal protein levels are reported in the urine protein electrophoresis (UPEP) results. Kappa and lambda free light chain levels, and the kappa-lambda free light chain ratio, are reported in results of the serum free light chain assay.

Strictly speaking, there are three different kinds of MGUS, with different criteria for each kind.

Non-IgM MGUS

This is MGUS where the abnormal plasma cells produce abnormal immunoglobulin that is not IgM. In most cases, the abnormal immunoglobulin will be either IgG or IgA.

For a diagnosis of non-IgM MGUS, all of the following criteria must be met.

1. Serum M-spike that is less than 3.0 g/dL (30 g/l) and that is not IgM type
2. Clonal bone marrow plasma cell percentage less than 10 percent
3. Absence of any organ-damage – such as elevated calcium levels in the blood, kidney damage, anemia, or bone lesions – or amyloidosis likely to be caused by the abnormal plasma cells in the patient's body

IgM MGUS

This is MGUS where the abnormal plasma cells produce abnormal immunoglobulin that is IgM.

For a diagnosis of non-IgM MGUS, all of the following criteria must be met.

1. Serum M-spike that is less than 3.0 g/dL (30 g/l) and that is IgM
2. Bone marrow lymphoplasmacytic cell percentage that is less than 10 percent
3. No evidence of anemia, constitutional symptoms, hyperviscosity, lymphadenopathy, hepatosplenomegaly, or other end-organ damage likely to be caused by the abnormal cells in the patient's body

Light-Chain MGUS

This is MGUS where the abnormal plasma cells produce only excess kappa or lambda free light chains, with no production of abnormal immunoglobulin

1. Kappa-lambda serum free light chain ratio that is less than 0.26 or greater than 1.65
2. Increased level of either the kappa level (if the kappa-lambda ratio is greater than 1.65) or the lambda level (if the kappa-lambda ratio is less than 0.26)
3. No sign in serum immunofixation test results of monoclonal immunoglobulin in the blood
4. Absence of any organ-damage – such as elevated calcium levels in the blood, kidney damage, anemia, or bone lesions – or amyloidosis likely to be caused by the abnormal plasma cells in the patient's body
5. Absence of any organ-damage – such as elevated calcium levels in the blood, kidney damage, anemia, or bone lesions – or amyloidosis likely to be caused by the abnormal plasma cells in the patient's body
6. Clonal bone marrow plasma cell percentage less than 10 percent
7. Urinary monoclonal protein level less than 500 mg per 24 hours