C4A and diabetes mellitus: No statistically significant differences were found for the other clinical features: sex (OR = 1.14, P = 0.389), monoclonal (OR = 1.33, P = 0.569), biclonal (OR = 0.75, P = 0.569), bone marrow puncture rate (OR = 1.09, P = 0.806), diabetes (OR = 0.78, P = 0.803), hemoglobin (WMD = 1.70, P = 0.094), complement C4 (WMD = 2.48, P = 0.667), kappa − chain value (WMD = − 8.99, P = 0.202), and lambda − chain value (WMD = 8.72, P = 0.159).