Background: Laboratory services play an important role in optimizing patient care today, and the importance of clinical laboratories is now widely accepted in medical practice. A critical value, originally described by Lundberg more than 30 years ago, refers to an abnormal test result that can lead to a serious life threat if not reported in a timely manner. In this study, we tried to determine the importance of critical values that can lead to a serious life threat with regard to their prevalence and frequency in laboratory tests of Iranian patients. Methods: In this cross-sectional study, the frequency of critical values in laboratory tests were determined and compared according to the type of laboratory parameter, age, sex, the inpatient/outpatient status, the related clinical ward, recurrence of critical values in the patient's test results, and the sampling working shift in Shahid Bahonar hospital in Kerman, Iran, in 2017 and 2018. Results: Among the tests, 0.2% had critical results. There was a significant relationship between the frequency of critical results with the patients' age (P = 0.002) and sex (P = 0.001) as well as with sampling working shift (P = 0.030) and admission ward (P = 0.001). Among the tests with critical values, the urea test was the most common with 32.2% critical value incidence. Conclusion:To maintain patient safety, proper recording of the results in laboratory tests and prompt reporting of critical values to the health care staff before repeating the test should be emphasized.