Jemal AlemuKidist Ababu2025-08-122025-08-122024-07-13https://etd.aau.edu.et/handle/123456789/6519Background: Newborns frequently experience unconjugated hyperbilirubinemia, which can lead to severe complications if left untreated. Phototherapy, a non-invasive and effective treatment, converts bilirubin into water-soluble forms. Despite its overall safety, phototherapy is discovered to be linked with various adverse effects and its effects on hematological profiles need more investigation. Objective: To assess the effect of phototherapy on hematological profile of newborns with unconjugated hyperbilirubinemia at Saint Paul’s Hospital Millennium Medical College, Addis Ababa, Ethiopia from February to April 2024. Methods: A cross-sectional study was conducted at Saint Paul’s Hospital Millennium Medical College from February to April 2024, involving 195 newborns exhibiting unconjugated hyperbilirubinemia to determine effects of phototherapy in their hematological profiles. The participants were selected using a convenient sampling technique. The study employed the Mindray BC-6800plus auto hematology analyzer. The analysis was performed using a paired t test in SPSS version 25, with a p-value of less than 0.05 considered statistically significant. Result: Out of a total 195 newborn participants 152 (77.9%) were male. Statistically significant changes in several hematological parameters determined. RBC counts decreased from 4.74 to 4.43 x 10^12 / L (p < 0.001), hemoglobin levels from 168.1 to 162.0 g/L (p < 0.001), and hematocrit from 45.17% to 44.19% (p = 0.003), with significant reductions at 24 and 48 hours (p < 0.01) but not at 72 hours. WBC counts increased from 9.90 to 11.02 x 10^9 / L (p < 0.001), along with a rise in lymphocyte percentage (p < 0.001) and a decrease in monocyte percentage decreased from 8.68% to 7.12% (p < 0.001) at 24 and 48 hours but not at 72 hours. Additionally, MCHC decreased from 372.2 g/L to 365.6 g/L (p = 0.022), and RDW decreased from 16.16% to 15.83% (p = 0.005), platelet count decrease from 220.52 to 207.72 10^9 / L (p < 0.001). Other parameters did not exhibit significant changes. Conclusion: Phototherapy was found to significantly decrease bilirubin levels, RBC count, hemoglobin levels, HCT, MCHC, monocyte percentage, and platelet count while WBC count increased, along with lymphocyte percentage. To optimize newborn care, it is essential to monitor hematological parameters closely during phototherapy. Key words: Phototherapy, Hematological Profile, Unconjugated hyperbilirubinemia, Newbornen-USPhototherapy Hematological ProfileUnconjugated hyperbilirubinemiaNewbornThesis