Background The recent emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in a rapid proliferation of serologic assays. However, little is known about their clinical performance. Here, we compared two commercial SARS-CoV-2 IgG assays. Methods 103 specimens from 48 patients with PCR-confirmed SARS-CoV-2 infections and 153 control specimens were analyzed using SARS-CoV-2 serologic assays by Abbott and EUROIMMUN (EI). Duration from symptom onset was determined by medical record review. Diagnostic sensitivity, specificity, and concordance were calculated. Results The Abbott SARS-CoV-2 assay had a diagnostic specificity of 99.4% (95% CI; 96.41–99.98%), and sensitivity of 0.0% (95% CI; 0.00–26.47%) at <3 days post symptom onset, 30.0% (95% CI; 11.89–54.28) at 3–7d, 47.8% (95% CI; 26.82–69.41) at 8–13d and 93.8% (95% CI; 82.80–98.69) at ≥14d. Diagnostic specificity on the EI assay was 94.8% (95% CI; 89.96–97.72) if borderline results were considered positive and 96.7% (95% CI; 92.54–98.93) if borderline results were considered negative. The diagnostic sensitivity was 0.0% (95% CI; 0.00–26.47%) at <3d, 25.0% (95% CI; 8.66–49.10) at 3–7d, 56.5% (95% CI; 34.49–76.81) at 3–7d and 85.4% (95% CI; 72.24–93.93) at ≥14d if borderline results were considered positive. The qualitative concordance between the assays was 0.83 (95% CI; 0.75–0.91). Conclusion The Abbott SARS-CoV-2 assay had fewer false positive and false negative results than the EI assay. However, diagnostic sensitivity was poor in both assays during the first 14 days of symptoms.

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Background Fentanyl is a synthetic opioid associated with illicit drug use and overdose deaths. The SEFRIA Immunalysis (IAL) and ARK fentanyl assays are both FDA-cleared, open channel immunoassays for fentanyl detection in urine. However, limited data are available in the literature comparing these assays. The objective of this study was to perform a direct comparison of these two fentanyl immunoassays. Methods IAL and ARK fentanyl immunoassays were performed on a Roche Cobas e602 automated chemistry analyzer. Repeatability and total imprecision were compared by diluting fentanyl into urine at concentrations above, below, and at the manufacturers’ cutoffs of 1.0 ng/mL. Cross-reactivity was assessed for norfentanyl and the fentanyl analogs acetylfentanyl, acrylfentanyl, and furanylfentanyl. Concordance was assessed in 90 patient samples using liquid chromatography-tandem mass spectrometry (LC-MS/MS) as the gold standard. Results Repeatability varied from 11.4%–17.8% on the IAL assay and 2.8%–5.5% on the ARK assay. Total imprecision was 18.9%–40.7% on the IAL assay and 2.9%–6.4% on the ARK assay. Both assays cross-reacted with acetylfentanyl (∼100%), acrylfentanyl (∼100%), and furanylfentanyl (∼20%), but only the ARK assay cross-reacted with norfentanyl (∼3%). An admixture of 0.5 ng/mL fentanyl and 6 ng/mL norfentanyl produced a positive result on the ARK assay. Total concordance between IAL and ARK for 90 tested patient samples was 93% (kappa = 0.85). Relative to LC-MS/MS, the IAL assay had a concordance of 90% (kappa = 0.79) and the ARK assay had a concordance of 94% (kappa = 0.88). Including norfentanyl in the LC-MS/MS confirmation increased the concordance of the ARK to 96% (kappa = 0.90). Conclusions The ARK assay recognized the metabolite norfentanyl, demonstrated superior precision, and had better concordance with LC-MS/MS compared to the IAL assay.

Background Serum free light chain (FLC) assays are used clinically to measure the concentration of κ and λ FLC in patients with suspected or diagnosed plasma cell proliferative disorders. Previous studies have demonstrated a loss of linearity in low concentration ranges of these assays. We hypothesized that this result could be caused by a matrix effect. Methods Recovery studies were performed for κ and λ FLC in both serum and saline using the Freelite assay (Binding Site) on a Cobas c502 system (Roche). Samples were analyzed either at the recommended dilution or undiluted. Follow-up studies were performed in varying matrices ranging from 0% to 100% saline. Retrospective patient data were analyzed to assess the impact on reported κ FLC, λ FLC, and κ/λ ratio. Results FLC in a serum matrix demonstrated underrecovery relative to samples diluted in saline for both κ and λ FLC. Of 255 patient samples with λ FLC measured undiluted (λ FLC <6.0 mg/L), an unexpected gap was observed in patient results between 2.0 and 6.0 mg/L. In addition, 23 patients measured serially with λ FLC between 2.0 and 6.0 mg/L demonstrated dramatic changes in κ/λ ratio, with no changes in κ FLC, likely because of the matrix effect. Conclusions The κ and λ Freelite assays exhibit a matrix effect when samples are tested undiluted, which has the potential to affect the κ/λ ratio. Consequently, our laboratory has stopped reporting λ FLC <6.0 mg/L.

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