# The Anti-Nucleocapsid IgG Antibody as a Marker of SARS-CoV-2 Infection for Hemodialysis Patients

## TL;DR

This study shows that anti-nucleocapsid IgG antibodies can detect prior SARS-CoV-2 infection in hemodialysis patients, but their effectiveness decreases over time.

## Contribution

Demonstrates the diagnostic accuracy of anti-IgG N antibodies in hemodialysis patients, a population with unique immune challenges.

## Key findings

- Anti-IgG N antibodies showed high diagnostic accuracy (AUC: 0.973–0.865) in detecting prior SARS-CoV-2 infection.
- Optimal cutoff for anti-IgG N was 0.01 AU/mL with sensitivity 1.00 and specificity 0.94.
- Diagnostic accuracy declined over time, indicating a need for tailored strategies in hemodialysis patients.

## Abstract

Background: Hemodialysis patients, due to impaired kidney function and compromised immune responses, face increased risks from SARS-CoV-2. Anti-nucleocapsid IgG (anti-IgG N) antibodies are a commonly used marker to assess prior infection in the general population; however, their efficacy for hemodialysis patients remains unclear. Methods: A retrospective study of 361 hemodialysis patients evaluated anti-IgG N antibodies for detecting prior SARS-CoV-2 infection. Antibody levels were measured using a chemiluminescence immunoassay (CLIA) over the four time points. Boxplots illustrated antibody distribution across sampling stages and infection status. Logistic regression and receiver operating characteristic (ROC) curve analysis determined diagnostic accuracy, sensitivity, specificity, and optimal cutoff values. Results: Among the 361 hemodialysis patients, 36 (10.0%) had SARS-CoV-2 infection. Sex distribution showed a trend toward significance (p = 0.05). Boxplot analysis showed that anti-IgG N levels remained low in non-infected patients but increased in infected patients, peaking at the third sampling. Anti-IgG N demonstrated high diagnostic accuracy (AUC: 0.973–0.865) but declined over time (p = 0.00525). The optimal cutoff at C1 was 0.01 AU/mL (sensitivity 1.00, specificity 0.94). Adjusted models had lower predictive value. Conclusions: Anti-IgG N antibodies showed high diagnostic accuracy for detecting prior SARS-CoV-2 infection in hemodialysis patients, though performance declined over time. These findings highlight the need for tailored diagnostic strategies in this vulnerable population.