Background: Human metapneumovirus (hMPV) is a major cause of acute respiratory infections in children and adults worldwide; however, no antiviral therapies or vaccines are currently available. Therefore, rapid and reliable diagnostic tools are required to support timely patient management and control outbreaks. Methods: We retrospectively evaluated GenBody hMPV Ag Rapid Test results using 165 consecutive clinical samples collected from patients with suspected respiratory infections between May and August 2024. Specimens were pre-characterized using a confirmatory reverse transcription-quantitative polymerase chain reaction (RT-qPCR) assay. Diagnostic performance was summarized using percent positive agreement (PPA), percent negative agreement (NPA), and overall percent agreement (OPA), with subgroup analyses by age and cycle threshold (Ct) groups. Results: The GenBody assay achieved a PPA of 92.7% (51/55), NPA of 100% (110/110), and OPA of 97.6% (161/165), with no false-positive results. Age-stratified analysis showed high PPA in infants (93.3%) and children (97%), whereas estimates in hMPV-positive adolescents (n = 2) and adults (n = 5) were less precise owing to the small sample size. In the Ct-stratified analysis, PPA was 100% for specimens with Ct < 28 (39/39), whereas all false-negative results occurred in the Ct > 28 group (12/16). Conclusion In this retrospective, single-center evaluation, the GenBody hMPV Ag Rapid Test showed high agreement with RT-qPCR, with reduced detection in specimens with higher Ct values. Further prospective studies and long-term stability assessments are warranted to confirm the performance across a broader range of clinical settings and storage conditions.