Background <p>Urinary tract infections (UTIs) are common diseases in the community that can lead to significant morbidity and mortality. UTIs can be classified as cystitis or pyelonephritis based on their location. Calprotectin is a protein released from monocytes and neutrophils that plays a role in the inflammatory response and antimicrobial defense. In this study it was aimed to investigate the diagnostic potential of calprotectin in distinguishing acute cystitis from acute pyelonephritis by evaluating serum and urine calprotectin levels in patients with UTI.</p> Methods <p>The study included adults aged 18 years and older who were admitted to our clinic with UTIs, including both pyelonephritis and cystitis, as well as healthy volunteers who served as the control group, between January 2024 and October 2024. In addition to routine biochemical and hematological tests, serum and urine calprotectin levels were measured. Data were analyzed using SPSS 21.0.</p> Results <p>A total of 88 participants were included in the study: 30 patients with pyelonephritis, 30 patients with cystitis, and 28 healthy controls. Female gender was predominant in all groups. Serum calprotectin levels were higher in patients with pyelonephritis and cystitis compared to the healthy control group (<i>p</i> &lt; 0.001). Urinary calprotectin levels were significantly higher in the cystitis group compared to the pyelonephritis and healthy controls (<i>p</i> &lt; 0.001). There was a positive and significant correlation between serum calprotectin and C-reactive protein (CRP) and procalcitonin (PCT) levels.</p> Conclusions <p>Our study suggests that calprotectin may be a useful biomarker in the diagnosis of UTI and the differentiation between lower and upper urinary tract infections, and sheds light on future large-scale studies.</p>