Convalescent Plasma Antibody Levels and the Risk of Death from Covid-19.
Level 3 - non-randomized controlled study
Retrospective cohort study analyzing mortality outcomes across antibody titer levels.
PubMed 33523609 · doi:10.1056/NEJMoa2031893
What was done
In a retrospective cohort study using a U.S. national registry, anti-SARS-CoV-2 IgG antibody levels were measured in convalescent plasma transfused into hospitalized adults with Covid-19 enrolled through July 4, 2020. The primary outcome was death within 30 days after transfusion across high, medium, and low antibody titer groups, stratified by mechanical ventilation status before transfusion.
What was found
Among 3,082 patients analyzed, 30-day mortality occurred in 115 of 515 patients (22.3%) in the high-titer group, 549 of 2,006 patients (27.4%) in the medium-titer group, and 166 of 561 patients (29.6%) in the low-titer group. Mechanical ventilation status moderated the association: among non-ventilated patients, high-titer plasma was associated with a lower 30-day mortality risk compared to low-titer plasma (relative risk, 0.66; 95% CI, 0.48 to 0.91), while no difference was observed in ventilated patients (relative risk, 1.02; 95% CI, 0.78 to 1.32).
Why it matters
This study provides evidence that clinical benefit from convalescent plasma in Covid-19 is titer-dependent and constrained by disease severity, demonstrating reduced mortality only with high antibody levels administered prior to mechanical ventilation.
Limits
As an observational retrospective study, it is subject to residual confounding and lacks an untreated or placebo-controlled control group. Baseline characteristics, time from symptom onset to transfusion, and co-interventions were not detailed in the abstract.
Cited by
- supports The FDA granted emergency use authorization for convalescent plasma for COVID-19 based on studies that lacked control groups.