Abstract—Dynamic changes in routine blood parameters in COVID-19 patients might be helpful to prognosticate deterioration in COVID-19 patients and evaluate treatment effect. Our study aimed to evaluate the temporal changes in red blood cell indices (MCV, MCH, MCHC, RDW) in COVID-19 patients and the association of other relevant clinical parameters. We analysed 17 medical records of COVID-19 patients in retrospect who required critical care from 1 January 2020 until 28 February 2021 in Hospital Tuanku Fauziah, Perlis, Malaysia. Data extracted include details with regards to escalation and de-escalation of oxygen therapy, clinical and laboratory parameters. There were three time points of interest in our study: (i) admission (Adm), (ii) highest mode of oxygen therapy (HighM), and (iii) weaned off oxygen therapy (WeanOxy). The result showed that the mean duration to clinical deterioration requiring the highest mode of oxygen delivery was 2.3 ±1.85 days and the highest escalation device for oxygen delivery was high flow nasal cannula (n=7, 41.2%). There was no statistically significant difference in RDW, MCV, MCH, and MCHC at different clinical time points, p>0.05. However, there was a statistically significant increment in TWBC trend between Adm-HighM-WeanOxy, χ2(2)=7.023, p=0.030. Our study did not find evidence of structural RBC changes reflected in RBC indices. However, recovery from COVID-19 was reflected in the rise of TWBC and ANC, similar to that observed with other viral illnesses.