International Journal of Medical Biochemistry, cilt.7, sa.2, ss.95-100, 2024 (Scopus)
Objectives: Urine is the most used matrix in drug analysis; however, it is susceptible to adulteration or tampering. Urine creatinine is the most important urine integrity parameter used as an indicator of dilution. This study aimed to evaluate the prevalence of diluted urine samples and the change in positivity after creatinine normalization. Methods: Urine samples screened by the LC-MS/MS method over a 3.5-year period (n=21,927) were included in the study. Positivity rates were evaluated in both total and diluted urine samples. Additionally, the impact of creatinine normalization on samples with substance concentrations above the limit of quantitation (LOQ) and below the cut-off was investigated. Results: A total of 350,832 tests were conducted on 21,927 urine samples, resulting in an overall positivity rate of 21.2% (n=4652). The ratio of diluted urine was 1.6% (n=343), with 61.5% (n=211) testing negative (