Prevalence of Monoclonal Gammopathy in Individuals Undergoing Routine Health Checkup in Brazil

Introduction: the occurrence of a monoclonal gammopathy (MG) is identified in approximately 3% of the population older than 50 years in US and Europe, and is usually an occasional finding. There is very few data about the prevalence of MG in the general population in Brazil and in Latin America, especially in individuals undergoing routine health checkups (HC).

Objectives: to evaluate the prevalence of MG in a general population undergoing routine HC in Brazil. Also, to compare demographic and laboratory data between individuals with and without MG.

Methods: between January and December 2014, patients with 45 years of age or older who presented for a routine HC at a general hospital in Sao Paulo, Brazil, had a blood sample tested for serum protein electrophoresis (SPEP). Independently of the previous general medical history of these individuals, the reason for going to the hospital was only the HC and not any specific medical diagnostic or treatment procedure. Samples with a positive SPEP for MG were further submitted to serum immunofixation (IF) and serum free light chain assays (FLC- Freelite ®-The Binding Site, UK). The study was approved by the IRB and all participants signed an informed consent.

Results: during the 12 months period, 3,095 individuals were studied, 2,393 men (77.3%) and 702 women (22.7%). MG was detected in 37 (1.2%), 31 men (1.3%) and 6 women (0.9%), p=0.35. The table shows the age distribution: there is an increase in the prevalence of MG for the older age groups, and this was statistically significant for individuals with 65 years or older when compared to those less than 55 years old.

Age Range (years) MG negative MG positive p

45-54 2,081 (99.0%) 20 (1.0%)

55-64 841 (98.5%) 13 (1.5%) 0.19

≥ 65 136 (97.1%) 4 (2.9%) 0.04

All 37 cases also presented a positive IF. The immunoglobulin involved was IgG in 28 cases (75.7%), IgM in 5 (13.5%), IgA in 2 (5.4%) and a double MG in 2 (5.4%).

The FLC ratio of the patients with a MG ranged from 0.28 to 38.50 and one case showed a very high abnormal FLC ratio of >55.0 (normal FLC ratio range = 0.26 to 1.65). The analysis showed an abnormal FLC ratio in 9 samples (24.3%).

The total gammaglobulin levels were significantly higher in the population with MG then in the population without MG (median results were respectively 1.16 g/dL and 1.06 g/dL, p< 0,001). There was no difference in the hemoglobin levels in the two groups (median levels respectively 14.4 g/dL and 14.7 g/dL, p=0.65).

Conclusion: it was observed that 1.2% of this general Brazilian population showed a MG. This prevalence is lower than reported in the medical literature in other countries for this age group, but may be explained by the also lower number of individuals older than 65 years studied. The presence of a MG increased significantly with age, as reported in other observations. These results are useful as a reference for epidemiological analysis of MG studies performed in the region. Larger regional studies should be performed, including analysis of environmental and behavioral factors.