Longitudinal evaluation of laboratory-based serological assays for SARS-CoV-2 antibody detection.

Serological assays for SARS-CoV-2 infection are now widely available for use in diagnostic laboratories. Limited data are available on the performance characteristics in different settings, and at time periods remote from the initial infection. Validation of the Abbott (Architect SARS-CoV-2 IgG), DiaSorin (Liaison SARS-CoV-2 S1/S2 IgG) and Roche (Cobas Elecsys Anti-SARS-CoV-2) assays was undertaken utilising 217 serum samples from 131 participants up to 7 months following COVID-19 infection. The Abbott and DiaSorin assays were implemented into routine laboratory workflow, with outcomes reported for 2764 clinical specimens. Sensitivity and specificity were concordant with the range reported by the manufacturers for all assays. Sensitivity across the convalescent period was highest for the Roche at 95.2-100% (95% CI 81.0-100%), then the DiaSorin at 88.1-100% (95% CI 76.0-100%), followed by the Abbott 68.2-100% (95% CI 53.4-100%). Sensitivity of the Abbott assay fell from approximately 5 months; on this assay paired serum samples for 45 participants showed a significant drop in the signal-to-cut-off ratio and 10 sero-reversion events. When used in clinical practice, all samples testing positive by both DiaSorin and Abbott assays were confirmed as true positive results. In this low prevalence setting, despite high laboratory specificity, the positive predictive value of a single positive assay was low. Comprehensive validation of serological assays is necessary to determine the optimal assay for each diagnostic setting. In this low prevalence setting we found implementation of two assays with different antibody targets maximised sensitivity and specificity, with confirmatory testing necessary for any sample which was positive in only one assay.

Apoptotic lymphocytes and CD34+ cells in cryopreserved cord blood detected by the fluorescent vital dye SYTO 16 and correlation with loss of L-selectin (CD62L) expression.

Discrimination between live and apoptotic cells is important for accurate determination of viable CD34(+) cells in hematopoietic stem cell transplant products. SYTO16 is a sensitive fluorescent dye for discriminating live from apoptotic leukocytes. The incidence of apoptotic leukocytes in paired samples of fresh and cryopreserved-thawed cord blood (CB) was determined by the SYTO16/7-AAD flow cytometric assay. Cell migration and expression of the cell homing molecule L-selectin (CD62L) was determined in relation to SYTO16 staining. SYTO16 detected significant proportions of apoptotic lymphocytes and CD34(+) cells in fresh and thawed CB buffy-coat samples that were not detected by 7-AAD. Compared to fresh CB, the proportion of apoptotic lymphocytes and CD34(+) cells significantly increased following thawing. Significantly higher proportions of live SYTO16(bright) lymphocytes and CD34(+) cells were found in the migrated cell population compared to the non-migrated population. Significantly fewer lymphocytes and CD34(+) cells expressed CD62L following thawing. Absence of CD62L expression was strongly correlated with apoptotic/SYTO16(dim) lymphocytes and CD34(+) cells. Cryopreserved-thawed CB contains significant proportions of apoptotic lymphocytes and CD34(+) cells that are not detected by 7-AAD. SYTO16 offers a sensitive method for discrimination of live from apoptotic leukocytes and assists in accurate assessment of CB quality and suitability for use in clinical transplantation.

Routine pulmonary function tests in young adolescents with asthma in general practice.

OBJECTIVE: To assess the value of performing routine pulmonary function tests by flow-loop spirometry in young adolescents with asthma. DESIGN: A prospective clinical study comparing clinical assessment and patients' self-reporting of asthma severity with the results of pulmonary function tests. SETTING: General practice in a small rural community of about 30,000 people. PATIENTS: Young adolescents with asthma, aged 10-15 years, were enrolled in the study over a two-year period from July 1993 to June 1995 when they presented for either elective, interval assessments or with an acute exacerbation of asthma. MAIN OUTCOME MEASURES: Discrepancy between (i) the doctor's and the patient's perception of asthma control (six scale measures) and the consequent management plans, and (ii) the results of pulmonary function tests that indicated less than adequate airway function (i.e., forced expiratory volume in one second as a percentage of predicted vital capacity for height and sex [FEV1%] less than 65% or average flow rate over the middle 50% of forced vital capacity as a percentage of predicted normal value [FEF25%-75%] less than 65%). RESULTS: Twenty-seven adolescents with asthma were assessed on a total of 37 occasions. The results of pulmonary function tests did not correlate with asthma symptoms and treatment in 11 of the 37 assessments (30%; 95% confidence interval [CI], 16%-47%). The 11 assessments were performed on eight patients. CONCLUSIONS: This small community-based study of adolescents with asthma supports the view that pulmonary function testing by flow-loop spirometry should be part of the routine assessment of acute and chronic asthmatics. Further study in a larger community is needed to clarify the frequency of over- and underestimation of asthma severity in this difficult age group.