Combining Rapid PCR and Antibody Tests Can Improve COVID-19 Diagnosis 

An interesting article published in the Journal of the American Medical Association October 13 by Jennifer Abbasi suggested that nose and throat swab polymerase chain reaction testing could miss up to 50% of COVID-19 cases.

This is due in part because the virus may already have cleared the upper respiratory tract, but by then, patients may have developed antibodies against the virus. 

An approach is suggested that combined rapid PCR and antibody testing could help physicians diagnose more cases from a recent small study of hospitalised patients with suspected COVID-19.

A University of Cambridge led team analysed previously collected data from the COVID study in which they clinically validated a simple amplification based assay known as SAMBA II, a rapid PCR test to detect severe SARS-CoV-2.  This point of care test is routinely used in clinical use here in the United Kingdom. 

The researchers also included stored sera from the subset of 45 patients which allowed antibody testing.  They collected the patient’s swabs and serum samples at a median of seven days after the symptoms emerged.  About half of this group had COVID-19. 

The SAMBA II test missed about one in five positive cases based on a reference standard that combined laboratory based PCR and neutralising antibody testing.  When the researchers combined the SAMBA II results with those from either of the two rapid lateral flow antibody assays, the positive predictive value increased to 100%. 

The point of care antibody test had 100% negative predictive agreement with a laboratory based neutralising antibody test in a separate analysis of fresh finger prick blood from 128 patients from suspected COVID-19 who were not part of the COVID X study. 

Importantly, the assays detected antibodies induced by a now dominant SARS-CoV-2 virus that was not widespread when the tests were developed. 

It is also suggested that combined testing could be important in the diagnosis and management of COVID-19. 

The London General Practice is exploring all currently available commercially available tests for COVID-19 and will bring them into clinical practice as soon as they have been passed by The London General Practice Clinical Governance Committee and have near 100% specificity and sensitivity.

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