Coagulation factor XIII (FXIII) circulates in plasma as a pro-transglutaminase heterotetrameric complex (FXIIIA2B2), which upon activation by thrombin and calcium covalently crosslinks preformed fibrin polymers. The heterotetrameric complex is composed of a catalytic FXIIIA2 subunit and a protective/regulatory FXIII-B2 subunit coded by F13A1 and F13B genes, respectively. The study aimed to assess the level of expression of the FXIII-A gene in seven Iraqi families affected with FXIII deficiency. Samples of whole blood were collected from seven Iraqi families that were characterized with F13 deficiency register in the Hemophilia Ward, Children Welfare Teaching Hospital, Medical City, Baghdad. These samples were divided into three groups according to the genotype, which included affected homozygous recessive and heterozygous with control healthy group. RNA was isolated from whole blood samples and gene expression levels of the F13 A1 gene was determined using quantitative Real-Time polymerase chain reaction (RT-qPCR), the result revealed that the expression levels of the F13A gene in heterozygous parents were significantly increased compared with the homozygous affected and control group. The (ROC) curve was analyzed in this study to determine the optimal cut-off value for F13 expression and showed a very good predictor for FXIII deficiency diagnosis with "Area under the ROC Curve." AUC equals 0.844 and p< 0.001.