الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Covid-19 pandemic has been causing millions of casualties around the world since its outbreak. Rapid and accurate diagnosis is crucial in fighting the spread of the disease and making decisions about isolation and treatment. RT-PCR is the most used diagnostic tool as it is the gold standard in viral detection. However, it is an expensive and labor intensive technique. Reaching rapid convenient diagnostic tool is the aim of many researchers.
The present study aimed to detect SARS-COV-2 N-antigen for diagnosis of COVID-19 through measuring SARS-CoV-2 N-antigen concentrations in people undergoing PCR testing for diagnosis of COVID-19, comparing between SARS-CoV-2 RT-PCR and N-antigen for diagnosis of COVID-19 and correlating between SARS-CoV-2 N-antigen level and clinical presentation of the studied subjects.
The current study was carried out over a period of 10 months from March 2021 to the end of December 2021. One hundred sixty-four individuals who were referred to laboratories to undergo PCR test for SARS-CoV-2 were recruited in the study. A structured interview was held with each participant to obtain demographic data and symptoms. Lab investigations and PCR results were obtained from medical records. Blood samples were collected from patients, sera were separated and stored at -80˚C till the assay was carried out. Quantitative detection of SARS-CoV-2 N-antigen was performed using Human SARS-CoV-2 N ELISA Kit manufactured by Invitrogen, Thermo Fisher Scientific, USA. Procedure was performed according to the manufacturer instructions and antigen concentrations were calculated from a standard curve. N antigen concentrations were compared to RT-PCR results (Ct values) and to the clinical features of the patients.
The results of the present study revealed that:
1. Ninety eight (59.8%) of the studied subjects were SARS-CoV-2 RT-PCR positive while SARS-CoV-2 N-antigen was detected in 31 (18.9%) of them.
2. Males constituted 58% of the studied subjects.
3. Participants’ age ranged from 18 to 99 years (median=63.5, IQR=20.2).
4. Regarding symptoms, 80 (48.8%) patients had fever, 94 (57.3%) patients had body aches and 64 (39%) patients had cough. Pneumonia was reported in 56 (34.1%) and hospitalization was required for 56 (34.1%) of the studied subjects.
5. Regarding laboratory investigations, 107 (65.2%) patients had lymphopenia, 29 (17.7%) patients had hypoxemia and 122 (84.1%) patients had elevated CRP levels.
6. The mean N-antigen concentration was higher in females (0.79748ng/ml) than in males (0.2819ng/ml).
7. The mean N-antigen concentration was 0.81576ng/ml in patients with fever, 0.706867ng/ml in patients with body aches, 0.74903ng/ml in patients with cough,
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0.78412ng/ml in patients with pneumonia and 0.8457ng/ml in patients who required hospitalization.
8. The mean N-antigen concentration was 0.327ng/ml in patients with lymphopenia, 0.91969ng/ml in patients with hypoxemia and 0.5916ng/ml in patients with elevated CRP levels.
9. Out of the PCR positive subjects, 30 (30.6%) were N-antigen positive while only one subject (1.5%) of the PCR negative patients was N-antigen positive.
10. The N-antigen test had a sensitivity of 30.6% and specificity of 98.5% with PPV of 96.8% and NPV of 48.9%.
11. The analysis of ROC curve revealed that at a cutoff point of >0.165ng/ml, specificity was 98%, sensitivity was 29.59% and AUC =0.648.
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6.2 Conclusion
It can be concluded from the present study that:
1. The mean N-antigen concentration was significantly higher in females than in males.
2. The N-antigen concentration was significantly associated with fever, body aches, cough, pneumonia, hospitalization, hypoxemia and CRP concentration.
3. The N-antigen concentration was not significantly associated with lymphopenia.
4. There was a significant fair agreement between SARS-CoV-2 PCR and N-antigen testing with poor sensitivity and high specificity for the N-antigen test.
5. There was a statistically significant negative correlation between Ct values of SARS-CoV-2 RT-PCR and N-antigen concentrations.
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6.3 Recommendations
from the results of the present study, the following recommendations are suggested:
1. Serum N-antigen is not recommended to be used solely as a diagnostic tool for COVID-19, it might be used with other investigations in low income countries where PCR is not available for diagnosis.
2. Further studies are required to test the performance of N-antigen assay using other specimens such as saliva, nasopharyngeal swab and urine.