A Simultaneous Extraction/Derivatization Strategy for Quantitation of Vitamin D in Dried Blood Spots Using LC-MS/MS: Application to Biomarker Study in Subjects Tested for SARS-CoV-2.

Vitamin D plays a critical role in bone development and maintenance, and in other physiological functions. The quantitation of endogenous levels of individual vitamin D and its metabolites is crucial for assessing several disease state conditions. With cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) leading to the coronavirus disease 2019 (COVID-19) pandemic, there are several studies that have associated lower levels of serum vitamin D with severity of infection in COVID-19 patients. In this context, we have developed and validated a robust LC-MS/MS method for simultaneous quantitation of vitamin D and its metabolites in human dried blood spot (DBS) obtained from participants tested for COVID-19. The chromatographic separation for vitamin D and metabolites was performed using an ACE Excel C18 PFP column protected with a C18 guard column (Phenomenex, Torrance, CA, USA). The mobile phase consisted of formic acid in water (0.1% v/v) as mobile phase A and formic acid in methanol (0.1% v/v) as mobile phase B, operated at a flow rate of 0.5 mL/min. Analysis was performed utilizing the LC-MS/MS technique. The method was sensitive with a limit of quantification of 0.78 ng/mL for all analytes, and had a large dynamic range (200 ng/mL) with a total run time of 11 min. The inter- and intraday accuracy and precision values met the acceptance criteria per the US Food and Drug Administration guidelines. Blood concentrations of 25(OH)D3, vitamin D3, 25(OH)D2, and vitamin D2 over a range of 2-195.6, 0.5-121.5, 0.6-54.9, and 0.5-23.9 ng/mL, respectively, were quantified in 909 DBS samples. In summary, our developed LC-MS/MS method may be used for quantification of vitamin D and its metabolites in DBS, and may be applied to investigations of the emerging role of these compounds in various physiological processes.

Self-Assessed Severity as a Determinant of Coronavirus Disease 2019 Symptom Specificity: A Longitudinal Cohort Study.

Coronavirus disease 2019 symptom definitions rarely include symptom severity. We collected daily nasal swab samples and symptom diaries from contacts of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) case patients. Requiring ≥1 moderate or severe symptom reduced sensitivity to predict SARS-CoV-2 shedding from 60.0% (95% confidence interval [CI], 52.9%-66.7%) to 31.5% (95% CI, 25.7%- 38.0%) but increased specificity from 77.5% (95% CI, 75.3%-79.5%) to 93.8% (95% CI, 92.7%-94.8%).

Detection and Kinetics of Subgenomic Severe Acute Respiratory Syndrome Coronavirus 2 RNA Viral Load in Longitudinal Diagnostic RNA-Positive Samples.

While detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by diagnostic reverse-transcription polymerase chain reaction (RT-PCR) is highly sensitive for viral RNA, the nucleic acid amplification of subgenomic RNAs (sgRNAs) that are the product of viral replication may more accurately identify replication. We characterized the diagnostic RNA and sgRNA detection by RT-PCR from nasal swab samples collected daily by participants in postexposure prophylaxis or treatment studies for SARS-CoV-2. Among 1932 RT-PCR-positive swab samples with sgRNA tests, 40% (767) had detectable sgRNA. Above a diagnostic RNA viral load (VL) threshold of 5.1 log10 copies/mL, 96% of samples had detectable sgRNA with VLs that followed a linear trend. The trajectories of diagnostic RNA and sgRNA VLs differed, with 80% peaking on the same day but duration of sgRNA detection being shorter (8 vs 14 days). With a large sample of daily swab samples we provide comparative sgRNA kinetics and a diagnostic RNA threshold that correlates with replicating virus independent of symptoms or duration of illness.