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Several recent studies aim at the detection of biological parameters that enable more precise diagnostics and stratification of monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM). The objective of our study was to assess the potential contribution of serum levels of Dickkopf-1 (DKK-1) in MGUS and MM from the point of more specific differentiation of both conditions, and the relationship of DKK-1 to selected laboratory parameters, individual forms and clinical stages of both conditions.The analyzed cohort consisted of 46 individuals with MGUS and 152 patients with MM at the time of diagnosis. For the assessment of serum levels of DKK-1 we used ELISA method. We assessed also serum levels of free light chains (FLC) κ and λ using the Freelite system, and β2-microglobulin (β2-M) using the Immulite 1000 method. For statistical estimation we used: Pearson χ2-test, U-test according to Mann-Whitney and Kruskal-Wallis test. Our analysis revealed that there was no significant difference between the levels of DKK-1 in MGUS risk groups (0-3) and between the states with different FLC concentration including the κ/λ index of monoclonality. In MM there was a significant relationship of DKK-1 to the level of hemoglobin (p0.008) but not to the levels of FLC, creatinine or β2-microglobulin. Within the Durie-Salmon staging system, there were significant differences of DKK-1 between the stages I vs. III (p=0.001) and I vs. II+III (p=0.002). In the International Staging System (ISS) there were significant differences only between stages 1 vs. 2+3 (p=0.045). Although there was no overall significant difference of DKK-1 levels between MGUS and MM, there was a difference between MGUS vs stage III (p=0.001) and II+III (p=0.001) according to Durie-Salmon, and also MGUS vs. stage 2 (p=0.005) and vs. stages 2+3 (p=0,012) according to ISS. There were no significant differences in DKK-1 between MGUS and initial/asymptomatic form of MM (stage I).Although there was a significant difference of serum levels of DKK-1 between MGUS and initial/asymptomatic stage of MM when compared to advanced stage MM, and in patients with different Hb levels, we do not find the evaluation of serum levels of DKK-1 useful for routine discrimination of MGUS and MM, and for the specification of temporary stratification systems.