Scan to discover online Background & Objective: Accurate and timely reporting of critical values is an important issue. There is some doubt whether repeat testing of critical values would offer any advantage over single testing or not. The aim of this study was evaluation of utility of routine repeat testing of critical values in our referral center and to compare probable variations in different working shifts. Methods: Clinical results of serum Potassium, Calcium, Blood Hemoglobin and Prothrombin Time (INR: International Normalized Ratio) were evaluated for three months. Results: Totally, 178, 96, 67 and 107 consecutive critical values for Potassium, Calcium, Hemoglobin and INR were reported, respectively. In potassium and Hemoglobin 5.05% and 1.17% of retest runs exceeded the acceptable tolerance limit. All of the calcium retest results were within the acceptable limit. For INR, 21/107 retest results did not meet the acceptable tolerance limit, nine still were critical. Afternoon working run performance was significantly better than the two others. Conclusion: Our observation suggests that routine repeat of hematology and chemistry critical test result is not necessary and may adversely affect patient safety measure. However, attention should be paid to results greater than analytical measurement range and all such results should be repeated before reporting.