eng Oriental Scientific Publishing Company Biomedical and Pharmacology Journal 0974-6242 2026-03-20 19 1 571 577 10.13005/bpj/3376 70805 article Aleem Mardas Khudhair 1 Abbas Razzaq Abed 1 Ibtisam Mohammed Hussein 2 Department of Nursing ,Technical Institute of Babylon , Al-Furat Al-Awsat Technical University, Babylon, Iraq. Department of Community health ,Technical Institute of Babylon , Al-Furat Al-Awsat Technical University, Babylon, Iraq. The coronavirus has spread to all countries around the world and has become a global pandemic, which has caused significant human and economic losses worldwide, international organizations have developed a mechanism for early diagnosis of this epidemic through the use of appropriate laboratory tests, contributing to the control of its spread. This study was conducted on 150 patients infected with COVID-19 between September to October 2021, ranging in age from 11 to 80 years. Laboratory analyses were conducted on them, including ferritin, D-dimer, C-reactive protein(CRP), and Leukocytes counts (WBCs). Statistical analysis used Correlations were assessed using Pearson's method at significance levels of p ≤ 0.01 and p ≤ 0.05to assess the relationship among the variables. The results indicated a significant statistical relationship between the studied variables. Specifically, a relationship was observed between patients' age and gender and their likelihood of contracting COVID-19, indicating that individuals of all age groups are affected by the virus. While the laboratory tests used in this study showed variation in results, the statistical relationship between elevated Leukocytes counts, Ferritin and C-reactive protein demonstrated significance at the p ≤ 0.01 level. On the other hand, findings revealed a statistically significant relationship (p ≤ 0.01) between CRP,  ferritin  and D-dimer . D-dimer was significantly correlated with CRP and ferritin at the p ≤ 0.01 level. The results demonstrated that there is an association between elevated levels of tested biomarkers (WBCs, ferritin ,D-dimer and CRP) in individuals infected with The novel coronavirus. https://biomedpharmajournal.org/vol19no1/a-laboratory-study-on-the-most-important-tests-for-covid-19-patients-and-their-interrelationships/ COVID-9 CRP D-dimer ferritin WBCs