Objectives: The study aimed to develop a validated LC–MS / MS method for the measurement of carbamazepine and carbamazepine-10,11-epoxide (CBZE) levels, to compare the carbamazepine concentrations measured by AbSciex API 3200 LC–MS/MS and Beckman Coulter Emit® 2000 immunoassay and to investigate the effect of carbamazepine concentrations on various hematological and biochemical parameters. Methods: For the measurement of carbamazepine and CBZE levels, a validated LC–MS / MS method was developed. Serum carbamazepine levels of patients were measured by AbSciex API 3200 LC–MS / MS and Beckman Coulter Emit® 2000 immunoassay. Biochemical, hematological parameters, and hormone levels were measured by Beckman-Coulter AU 5800 (Beckman Coulter, Brea, USA), Beckman Coulter LH 780 (Beckman Coulter, Miami, FL, USA), and Cobas 6000 (Roche Diagnostics, Germany) analyzers, respectively. Results: The imprecision values for all analytes were less than 7.0 %. The correlation coefficient between the methods was 0.981 (95 % confidence interval: 0.975 to 0.985). Linear regression analysis demonstrated highly significant associations of carbamazepine concentrations with albumin (B = −0.300, p = 0.040), calcium (B = −0.262, p = 0.004), phosphorus (B = −0.241, p = 0.022), WBC (B = −0.288, p = <0.001), PLT (B = −0.236, p = 0.003), RBC (B = −0.257, p = 0.001), NEU% (B = −0.289, p = <0.001), LYM% (B = −0.268, p = 0.001), D vitamini (B = −0.344, p = 0.006) levels. Conclusions: A robust, rapid, and simple method has been developed. Our study revealed that carbamazepine and its metabolite have a significant correlation and likely impact on bone metabolism, blood cell counts, serum protein, albumin levels, and electrolyte concentrations.