In this work, it has been shown that it is possible to determine the radiation doses in human blood exposed to internal or external ionizing radiation treatment, both directly and retrospectively. OSL counts from the waste blood of a patient injected with a radiopharmaceutical for diagnostic or treatment purposes and from a blood sample having a laboratory-injected radiation dose were both used for measurements. The dose values obtained the bloods were found as similar to 0.46 Gy for the 1-5Gy dose range and as similar to 0.51 Gy for the 0.143-0.858 Gy dose range using the optically stimulated luminescence technique. The blood aliquots from a healthy person were exposed to different external laboratory doses. The dose values corresponding to a 10Gy laboratory dose from the aliquots exposed to external radiation were found as 10.94 +/- 3.30 Gy for Disc 3 and 10.79 +/- 3.28 Gy for Disc 1. This study shows that the dose received by a person can be measured simply and retrospectively, using only a very small amount of blood. The results may have important ramifications for the medicine and healthcare fields in particular.