Background: COVID-19 infects all patients of all ages including the elderly. Several studies have shown that complete blood counts can be used as a marker of the severity of COVID-19. This study aims to examine complete blood counts with the severity of COVID-19 in elderly patients at the Tabanan Regional General Hospital (RSUD) in 2021. Methods: This research was conducted using an retrospective study method, using 277 samples taken from secondary data (patient medical records) at Tabanan General Hospital. The independent variables of study including haemoglobin, haematocrit, leukocytes, relative lymphocyte levels, relative neutrophil levels, neutrophil lymphocyte ratio (NLR), relative eosinophil levels, relative basophil levels, relative monocyte levels, platelets, and depending variable is the severity of the patient, divided to moderate, severe, critically ill. Data analysis using SPSS version 26 for Windows. Results: Complete blood counts were significantly correlated with Lymphocytes (r2 = 0,069; p < 0,001), Monocyte (r2 = 0,045; p < 0,001), Leukocyte (r2 = 0,037; p = 0,001), NLR (r2 = 0,03; p = 0,004), Eosinophil (r2 = 0,022; p = 0,013), and Haematocrit (r2 = 0,069; p = 0,022). Conclusion: In this study, complete blood count (leukocytes, NLR, haematocrit with a positive value correlation, and lymphocytes, eosinophils, monocytes with a negative value correlations) can be used as predictors to assess the severity of COVID-19 patients. However, neutrophils, basophils, haemoglobin, and platelets were not correlated significantly. Latar Belakang: COVID-19 menginfeksi semua pasien dari segala usia termasuk lansia. Beberapa studi menunjukkan bahwa pemeriksaan darah lengkap dapat dipergunakan sebagai penanda derajat keparahan COVID-19. Penelitian ini bertujuan untuk mengevaluasi pemeriksaan darah lengkap dengan derajat keparahan COVID-19 pada pasien lansia di Rumah Sakit Umum Daerah (RSUD) Tabanan tahun 2021. Metode: Penelitian ini dilakukan dengan metode studi retrospektif menggunakan 277 sampel yang diambil dari data sekunder rekam medis pasien di RSUD Tabanan. Variabel independen penelitian meliputi hemoglobin, hematokrit, leukosit, kadar limfosit relatif, kadar neutrofil relatif, neutrofil limfosit ratio (NLR), kadar eosinofil relatif, kadar basofil relatif, kadar monosit relatif, trombosit, dan dependent derajat keparahan pasien yaitu sedang, berat, kritis. Analisis data memakai SPPS versi 26 untuk Windows. Results: Pemeriksaan darah lengkap menunjukkan hasil yang bermakna pada Limfosit (r2 = 0,069; p < 0,001), Monosit (r2 = 0,045; p < 0,001), Leukosit (r2 = 0,037; p = 0,001), NLR (r2 = 0,03; p = 0,004), Eosinofil (r2 = 0,022; p = 0,013), dan Hematokrit (r2 = 0,069; p = 0,022). Conclusion: Pada penelitian ini pemeriksaan darah lengkap (leukosit, NLR, hematokrit dengan korelasi positif, dan limfosit, eosinofil, monosit dengan korelasi nilai negatif) dapat digunakan sebagai prediktor untuk menilai derajat keparahan pasien COVID-19. Akan tetapi neutrofil, basofil, hemoglobin, dan trombosit tidak berkorelasi secara bermakna.