Association of SARS-COV 2 Real-Time PCR Cycle Threshold (Ct) Values with the Clinical and Laboratory Profiles of Confirmed COVID-19 Patients Admitted in Tertiary Infectious Disease Hospital in Manila: A Retrospective Study

Abstract

Background and Objectives. COVID-19 has quickly spread over the world and became an unprecedented burden on health care systems. COVID-19 diagnosis necessitates the use of precise testing methods such as RT-PCR. This method is generally reported as positive or negative, however, studies have shown its semi-quantitative capability through Ct values. This study determined an association that exists between the Ct values, clinical features, and laboratory findings among COVID-19 patients admitted in a tertiary infectious disease hospital in Manila, Philippines. This attempts to further explore the utility of RT-PCR in disease severity classification and diagnosis.

Methods. This was an observational retrospective study that utilized a purposive sampling method, wherein patients were selected based on the DOH case definition of confirmed COVID-19, and were stratified according to disease severity. Baseline laboratory data of the patients were gathered from medical records covering the period of June 2021 to January 2022 using a Data Collection Form. Chi-square test was used to measure the degree of association between the groups and categorical variables. Regression Analysis was used to identify predictors for certain variables. SPSS Statistics for Windows, Version 25.0 was utilized for the statistical analysis.

Results. The total WBC, neutrophil, lymphocyte and monocyte counts, serum urea, LDH, CRP and PTT were found to be predictors of COVID-19 severity. There was no significant difference observed between the disease severity and the patient’s clinical outcome. All routine laboratory tests that were taken at baseline (ORF Gene, N-Gene, Hematocrit, White Blood Cells, Neutrophil, Lymphocyte, Monocyte, Platelet Count, Urea, Creatinine, SGPT, SGOT, Na, K, LDH, Ferritin, C Reactive Protein, Procalcitonin, D-Dimer, PT, PTT) were not significant predictors of the clinical outcome. Although WBC, neutrophil, lymphocyte, and monocyte count, urea, LDH, CRP, and PTT were predictors  of disease severity. The study also reported that the odds of having severe to critical disease increases by 20.6% for every one unit increase in neutrophil count, and 17.4% for every one unit increase in lymphocyte count. Among the laboratory parameters, neutrophil count (p=0.010654063) and urea (p= 0.04149874 have direct relationship with the N gene Ct values while Orf gene Ct Values have direct relationship with lymphocyte count (p=0.01269027). Similarly, regression showed that as monocyte count, creatinine levels, and serum ferritin decrease, Ct values increase. Sex was found to not be a significant predictor of disease severity and clinical outcome. There was also no significant difference observed between the disease severity and the patient’s clinical outcome.

Conclusion. The study showed that the Ct values for both ORF and N genes were not significant predictors of both disease severity and clinical outcome. However, ORF gene Ct values have direct relationship with lymphocyte counts while N gene Ct values have direct correlation with neutrophil count and urea levels. Similarly, monocyte, creatinine, and ferritin are negatively correlated with Ct values. It is important to monitor the patient’s laboratory biomarkers in order to determine the proper course of treatment and management for each case.