key: cord-0871020-gek3zdkj
authors: Morshed, Muhammad; Sekirov, Inna; McLennan, Meghan; Levett, Paul N; Chahil, Navdeep; Mak, Annie; Carruthers, Erin; Pidduck, Tamara; Kustra, Jesse; Laley, Jonathan; Lee, Min-Kuang; Chu, Kenneth; Burgess, Fred; Vijh, Rohit; Willis, Lori; Wada, Ray; Blancaflor, Rosemarie; Boraston, Suni; Hayden, Althea; Krajden, Mel
title: Comparative analysis of capillary versus venous blood for serologic detection of SARS-CoV-2 antibodies by rPOC lateral flow tests
date: 2021-01-28
journal: Open Forum Infect Dis
DOI: 10.1093/ofid/ofab043
sha: 1f0bf94a98ee4d6371c19c627b8627a2cb3742e1
doc_id: 871020
cord_uid: gek3zdkj

A comparison of rapid point of care serology tests using finger prick and venous blood was done on 278 participants. In a laboratory setting, IgG sensitivity neared 100%; however, IgG sensitivity dramatically dropped (82%) in field testing. Possible factors include finger prick volume variability, hemolysis, cassette readability and operator training.

M a n u s c r i p t 3 As the number of COVID-19 cases continues to increase worldwide, the need for fast, easy-to-use and accurate tests is urgent. Rapid point of care (rPOC) lateral flow tests measure serum antibodies to SARS-CoV-2 and a number of them are currently available. Most cassettes are designed to detect separately and simultaneously IgM and IgG antibody types and they have been used in a variety of studies to provide estimates of population seroprevalence. In acute cases, when a patient is repeatedly negative for PCR but symptomatic, a highly sensitive and specific rPOC could be utilized as a diagnostic method for those with difficult venous access. rPOC can be also be used for surveillance purposes in hard to reach populations that have no access to laboratories, or to satisfy pre-travel requirements. The literature suggests that most of the comparative evaluations on rPOC tests were done in laboratory settings [1] [2] [3] . In order to evaluate the performance of rPOC in the field, the British Columbia Centre for Disease Control Public Health Laboratory (BCCDC PHL) conducted a comparative assessment of the performance of rPOC lateral flow assays in a laboratory (using venous blood samples) versus a field (using fingerpick capillary blood) setting. Field testing was conducted in 2 long-term care facilities (LTCFs) affected by COVID-19 outbreaks [4] .

We conducted initial laboratory-based evaluations with a total of 142 venous blood samples, with subsequent evaluation in the field on 278 capillary blood samples. Briefly, 3 rPOC products were screened in the laboratory using venous samples obtained from known COVID-19 patients at 0-7, 8-14 and >14 days post-illness onset (total n=79), as well as pre-pandemic negative samples stored at BCCDC PHL tested for other serology prior to 2019, which included samples with seropositivity to other common pathogens, such as HIV, HCV, syphilis, etc. (n=63) ( Table 1 ). Some of those negative samples, such as Toxoplasma IgM, West Nile Virus IgM, Chikungunya IgM were selected because they are notorious for exhibiting non-specific reactivity against many other pathogens ( Table 2 ). All rPOC products used in this study could detect both IgM and IgG on the same cassette. Positive patients were confirmed by BCCDC PHL in-house laboratory developed RT PCR [5] . Three of the products tested -Artron Diagnostics Inc. (Canada) referred as Artron, BioCan Diagnostics Inc.

(Canada) referred as BioCan and Rapid Response BTNX (China) referred as BTNXyielded very promising analytical performance with 91%-95% sensitivity and 93%-100% specificity ( Table 1) . All Based on laboratory performance, secure supply chain and product cost, the Artron Diagnostics Inc.

product was selected for a dual laboratory/field trial, with the field trial conducted in 2 LTCFs with confirmed COVID-19 outbreaks. In LTCF rPOC tests were performed by trained laboratory medicine technologists, who were trained in their performance prior to conducting testing. The BioCan Diagnostics Inc. and BTNX products were also tested using only the venous blood samples collected at the LTCF.

Samples were collected on from residents and staff at least 14 days after symptoms onset (for known PCR-confirmed COVID-19 patients). Samples comprised those from known COVID-positive patients (PCR-confirmed) and from patients of "unknown" status (either PCR-negative or never tested by PCR). "Unknown" status patients were classified as "presumed positive" (consensus positive SARS-CoV-2 serology on all 4 high throughput automated platforms [ (1) LIAISON® SARS-CoV-2 S1/S2 IgG (DiaSorin IgG; DiaSorin, Italy); 2) ARCHITECT SARS-CoV-2 IgG (Abbott IgG; Abbott, USA);

3) VITROS® Anti-SARS-CoV-2 Total (Ortho T) and 4) SARS-CoV-2 Total Assay (Siemens T;

Siemens, USA)] and "presumed negative" (consensus negative SARS-CoV-2 serology on all 4 high throughput automated platforms). Any samples with discrepant results on any of the 4 high throughput automated platforms were excluded from the analysis.

In the field, we found that finger-prick-based sensitivity of the Artron rPOC test was overall inferior to that done with venous blood in a laboratory setting (Table 3) . Finger prick IgG sensitivity dropped to ~83% (specificity 99%). When paired venous samples were tested in the laboratory on Artron cassettes, the sensitivity did improve to ~89% , but still did not reach that observed in the initial validation study (Table 1) . IgM sensitivity in the field setting was higher than in the in-laboratory serum performance on paired samples (~67% vs. ~58%), but both were markedly lower than in the A c c e p t e d M a n u s c r i p t 5 initial validation study (Table 1) . There was also a small drop in specificity for IgM in the field vs. inlaboratory setting on paired samples (91.5% vs. 92.6%). When BioCan and BTNX rPOC cassettes were trialed on a large subset (n dependent on availability of cassettes) of the same venous samples, the performance was also inferior to that previously observed in the laboratory evaluation.

Specifically, the sensitivity of both BioCan and BNTX cassettes in detecting COVID-19 IgM 14 days after symptoms-onset was markedly lower than that in the validation study (data not shown).

Furthermore, additional BioCan and BTNX cassettes procured for the LTCF evaluation were noted to have variable appearance and inferior quality to that of the first batch trialed in the laboratory.

Our results demonstrate poorer performance of rPOC assays under field settings relative to what can be achieved in the laboratory, possibly due to reduced standardization in blood inoculum in the field. 

Evaluation of six commercial mid to high volume antibody and six point of care lateral flow assays for detection of SARS-CoV-2 antibodies

Clinical and laboratory evaluation of SARS-CoV-2 lateral flow assays for use in a national COVID-19 seroprevalence survey

Four point-of-care lateral flow immunoassays for diagnosis of COVID-19 and for assessing dynamics of antibody responses to SARS-CoV-2

Serological survey following SARS-COV-2 outbreaks at long-term care facilities in metro Vancouver, British Columbia: Implications for outbreak management and infection control policies

A c c e p t e d M a n u s c r i p t 7