Abstract: Background　The diagnosis of sarcopenia relies on the 2019 Asian Working Group for Sarcopenia criteria; however, equipment limitations and operational difficulties in the inpatient setting underscore the urgent need for simpler serum biomarkers. As a potential target, the diagnostic value and incremental contribution of Dickkopf-3 (DKK3) in older male hospitalized patients remain unclear. Objective　To evaluate the diagnostic value of serum DKK3 alone and in combination with clinical indicators for sarcopenia in very elderly male inpatients. Methods　A case-control study was conducted among very elderly (≥80 years) male patients hospitalized in the Geriatric Ward of PLA General Hospital from September 2022 to October 2023. The 2019 Asian Working Group for Sarcopenia criteria were used as the diagnostic gold standard. Clinical data were collected and serum DKK3 concentrations were measured. Receiver operating characteristic (ROC) curves were plotted to evaluate the diagnostic efficacy of DKK3 alone and in combination with a clinical model (grip strength + BMI + age + bed rest duration). The Delong test was used to compare the area under the curve (AUC), and the net reclassification improvement index (NRI) was calculated to assess the incremental diagnostic value. Results　A total of 293 patients were enrolled, with a sarcopenia prevalence of 53.24% (156/293). The median serum DKK3 level in the sarcopenia group was 1 126.00 (569.60, 1 414.00) pg/mL, compared to 1 225.00 (761.90, 1 552.00) pg/mL in the non-sarcopenia group, with no statistically significant difference between the two groups (P=0.083). The AUC of DKK3 alone for diagnosing sarcopenia was 0.559 (95% CI: 0.493 - 0.625), with an optimal cut-off value of 1 058.7 pg/mL, yielding a sensitivity of 53.8% and a specificity of 59.1%. The clinical model (Grip strength, body mass index BMI, age, and bedridden time) achieved an AUC of 0.860 (95% CI: 0.817 - 0.903), while the combined model (+DKK3) achieved an AUC of 0.861 (95% CI: 0.818 - 0.904). The Delong test showed no statistically significant difference in AUC between the two models (P=0.659), and the NRI was 0.092 5. Conclusion　Serum DKK3 alone has limited diagnostic efficacy for sarcopenia in very elderly male inpatients and does not provide statistically significant incremental diagnostic value beyond grip strength and BMI. The clinical model combining grip strength and BMI is simple, effective, and suitable for promotion in primary care settings.