Tehran University of Medical Sciences Acta Biochimica Iranica 0001-5261 3 4 2025 12 18 242 247 Jamal Amri 1. Department of Clinical Biochemistry, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Mojgan Torabi Farsani Clinical Laboratory, Yas Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. Mahdi Aminian 1. Department of Clinical Biochemistry, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. 2026 02 05 Objectives: Zinc (Zn) is a vital trace element, and its accurate measurement in biological samples is important for diagnosing Zn deficiency. However, the difference in Zn concentration between serum and plasma samples and the effect of anticoagulants on results are major methodological challenges. The aim of this study was to compare the effect of common anticoagulants (EDTA, citrate and heparin) on Zn concentration in blood samples using a routine colorimetric method. Methods: This research was conducted on 20 healthy volunteers (10 women and 10 men). Samples of serum, EDTA, citrate and heparin plasma were collected and Zn levels were measured using a routine colorimetric method based on 5‑Br‑PAPS. Results: The results of this study showed that Zn concentrations in EDTA‑ and citrate‑anticoagulated plasma were significantly lower than those measured in serum (P<0.05). In contrast, no statistically significant difference was observed between serum and heparin‑anticoagulated plasma (P>0.05). Spearman’s correlation analysis showed a strong positive correlation between serum Zn concentrations and those measured in heparin (r=0.831, P<0.001) and citrate (r=0.704, P<0.01) plasma samples, whereas the correlation between serum and EDTA plasma was positive but weak and not statistically significant (r=0.099, P>0.05). Conclusion: The choice of anticoagulant is a critical pre-analytical factor in Zn measurement using colorimetric methods. These findings show that chelating anticoagulants like EDTA and citrate spuriously lower Zn concentration, whereas heparin‑anticoagulated plasma yields Zn measurements that are comparable to those obtained in serum. These results are of great importance for the accurate interpretation of results in clinical laboratories. https://abi.tums.ac.ir/index.php/abi/article/view/180 https://abi.tums.ac.ir/index.php/abi/article/download/180/126