The CKD-EPI 2021 Equation and Other Creatinine-Based Race-Independent eGFR Equations in Chronic Kidney Disease Diagnosis and Staging

BACKGROUND

Recent debate on the race correction factor in creatinine-based estimated glomerular filtration rate (eGFR) has led to the development of a new race-independent equation (Chronic Kidney Disease Epidemiology Collaboration, CKD-EPI_2021). Previously, some institutions have already modified the early version of the CKD-EPI or Modification of Diet in Renal Disease (MDRD) equations by removing the race factors (CKD-EPI_2009_non-Black (NB), MDRD_NB) for Black populations although this approach remains controversial.

METHODS

In this study, the CKD-EPI_2009_NB, MDRD_NB, and European Kidney Function Consortium (EKFC) equations were compared directly with the CKD-EPI_2021 equation in eGFR calculation, chronic kidney disease (CKD) diagnosis, and staging in a local population.

RESULTS

These 3 previous methods underestimated eGFR compared to CKD-EPI_2021 for eGFR < 90 mL/min/1.73 m2 but overestimated eGFR at the high end (>120 mL/min/1.73 m2). Around the CKD diagnosis cutoff (60 mL/min/1.73 m2), both MDRD_NB and EFKC equations resulted in an increase in CKD cases compared to CKD-EPI_2021. CKD-EPI_2009_NB demonstrated a similar trend although the difference was not statistically significant. In a population with low eGFR (<60 mL/min/1.73 m2), the EKFC equation showed a CKD staging pattern significantly different from that by CKD-EPI_2021, but all 3 previous methods resulted in a similar number of end-stage renal failure cases. In general, the EKFC equation demonstrated a weaker agreement in eGFR calculation and concordance in classification with the CKD-EPI_2021 equation than MDRD_NB and CKD-EPI_2009_NB.

CONCLUSIONS

Our study provides a direct visual comparison to demonstrate the potential clinical impact between 3 previously used race-independent methods and the CKD-EPI_2021 equation and aids the communication with healthcare providers during the implementation of this new equation.

Assessment of serum total 25-hydroxyvitamin D assays for Vitamin D External Quality Assessment Scheme (DEQAS) materials distributed at ambient and frozen conditions

The Vitamin D External Quality Assessment Scheme (DEQAS) distributes human serum samples four times per year to over 1000 participants worldwide for the determination of total serum 25-hydroxyvitamin D [25(OH)D)]. These samples are stored at -40 °C prior to distribution and the participants are instructed to store the samples frozen at -20 °C or lower after receipt; however, the samples are shipped to participants at ambient conditions (i.e., no temperature control). To address the question of whether shipment at ambient conditions is sufficient for reliable performance of various 25(OH)D assays, the equivalence of DEQAS human serum samples shipped under frozen and ambient conditions was assessed. As part of a Vitamin D Standardization Program (VDSP) commutability study, two sets of the same nine DEQAS samples were shipped to participants at ambient temperature and frozen on dry ice. Twenty-eight laboratories participated in this study and provided 34 sets of results for the measurement of 25(OH)D using 20 ligand binding assays and 14 liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. Equivalence of the assay response for the frozen versus ambient DEQAS samples for each assay was evaluated using multi-level modeling, paired t-tests including a false discovery rate (FDR) approach, and ordinary least squares linear regression analysis of frozen versus ambient results. Using the paired t-test and confirmed by FDR testing, differences in the results for the ambient and frozen samples were found to be statistically significant at p < 0.05 for four assays (DiaSorin, DIAsource, Siemens, and SNIBE prototype). For all 14 LC-MS/MS assays, the differences in the results for the ambient- and frozen-shipped samples were not found to be significant at p < 0.05 indicating that these analytes were stable during shipment at ambient conditions. Even though assay results have been shown to vary considerably among different 25(OH)D assays in other studies, the results of this study also indicate that sample handling/transport conditions may influence 25(OH)D assay response for several assays.

Interlaboratory comparison of 25-hydroxyvitamin D assays: Vitamin D Standardization Program (VDSP) Intercomparison Study 2 - Part 1 liquid chromatography - tandem mass spectrometry (LC-MS/MS) assays - impact of 3-epi-25-hydroxyvitamin D3 on assay performance

An interlaboratory comparison study was conducted by the Vitamin D Standardization Program (VDSP) to assess the performance of liquid chromatography - tandem mass spectrometry (LC-MS/MS) assays used for the determination of serum total 25-hydroxyvitamin D (25(OH)D), which is the sum of 25-hydroxyvitamin D₂ (25(OH)D₂) and 25-hydroxyvitamin D₃ (25(OH)D₃). A set of 50 single-donor samples was assigned target values for concentrations of 25(OH)D₂, 25(OH)D₃, 3-epi-25-hydroxyvitamin D₃ (3-epi-25(OH)D₃), and 24R,25-dihydroxyvitamin D₃ (24R,25(OH)₂D₃) using isotope dilution liquid chromatography - tandem mass spectrometry (ID LC-MS/MS). VDSP Intercomparison Study 2 Part 1 includes results from 14 laboratories using 14 custom LC-MS/MS assays. Assay performance was evaluated using mean % bias compared to the assigned target values and using linear regression analysis of the test assay mean results and the target values. Only 53% of the LC-MS/MS assays met the VDSP criterion of mean % bias ≤ |±5%|. For the LC-MS/MS assays not meeting the ≤ |±5%| criterion, four assays had mean % bias of between 12 and 21%. Based on multivariable regression analysis using the concentrations of the four individual vitamin D metabolites in the 50 single-donor samples, the performance of several LC-MS/MS assays was found to be influenced by the presence of 3-epi-25(OH)D₃. The results of this interlaboratory study represent the most comprehensive comparison of LC-MS/MS assay performance for serum total 25(OH)D and document the significant impact of the lack of separation of 3-epi-25(OH)D₃ and 25(OH)D₃ on assay performance, particularly with regard to mean % bias.

Assessment of serum total 25-hydroxyvitamin D assay commutability of Standard Reference Materials and College of American Pathologists Accuracy-Based Vitamin D (ABVD) Scheme and Vitamin D External Quality Assessment Scheme (DEQAS) materials: Vitamin D Standardization Program (VDSP) Commutability Study 2

An interlaboratory study was conducted through the Vitamin D Standardization Program (VDSP) to assess commutability of Standard Reference Materials® (SRMs) and proficiency testing/external quality assessment (PT/EQA) samples for determination of serum total 25-hydroxyvitamin D [25(OH)D] using ligand binding assays and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A set of 50 single-donor serum samples were assigned target values for 25-hydroxyvitamin D2 [25(OH)D2] and 25-hydroxyvitamin D3 [25(OH)D3] using reference measurement procedures (RMPs). SRM and PT/EQA samples evaluated included SRM 972a (four levels), SRM 2973, six College of American Pathologists (CAP) Accuracy-Based Vitamin D (ABVD) samples, and nine Vitamin D External Quality Assessment Scheme (DEQAS) samples. Results were received from 28 different laboratories using 20 ligand binding assays and 14 LC-MS/MS methods. Using the test assay results for total serum 25(OH)D (i.e., the sum of 25(OH)D2 and 25(OH)D3) determined for the single-donor samples and the RMP target values, the linear regression and 95% prediction intervals (PIs) were calculated. Using a subset of 42 samples that had concentrations of 25(OH)D2 below 30 nmol/L, one or more of the SRM and PT/EQA samples with high concentrations of 25(OH)D2 were deemed non-commutable using 5 of 11 unique ligand binding assays. SRM 972a (level 4), which has high exogenous concentration of 3-epi-25(OH)D3, was deemed non-commutable for 50% of the LC-MS/MS assays.

Analytical and Clinical Analysis of Two Automated Anti-SARS-CoV-2 Immunoassays in Pre-Pandemic and Pandemic Patient Populations

Background

In the absence of a safe, effective vaccine, the worldwide spread of COVID-19 (SARS-CoV-2) infection will continue. Laboratory tests with ideal precision, sensitivity, and specificity should be used in public health and clinical settings to gauge the extent of virus exposure. Toward this end, we evaluated the analytical and clinical performance of the Abbott SARS-CoV-2 IgG and the Roche Anti-SARS-CoV-2 immunoassays.

Methods

Quality control, pooled COVID-19, and non-COVID-19 patient specimens were used for the imprecision study. 246 specimens from 70 patients with COVID-19 diagnosis were tested to study the sensitivity. 73 non-COVID-19 control specimens were measured to study the specificity. All specimens were analyzed by both assays.

Results

Total analytic variability (CV) of the negative and positive controls were 5.5% and 3.6% for the Abbott assay and 4.5% and 1.9% for the Roche assay. Both assays demonstrated 100% qualitative reproducibility of negative and positive controls. The clinical specificities of the Abbott and the Roche assays were 100% (95% CI: 94% - 100%) and 97% (95% CI: 90% - 100%), respectively. The clinical sensitivities of the Abbott assay were 49% (95% CI: 41% - 56%), 86% (95% CI: 74% - 93%) and 100% (95% CI: 76% - 100%) for samples collected at 0-6 days, 7-13 days and ≥14 days after the first RT-PCR, while the sensitivities of the Roche assay were 55% (95% CI: 47% - 62%), 86% (95% CI: 74% - 93%) and 100% (95% CI: 76% - 100%).

Conclusions

This study demonstrates similar analytical and clinical performance of the Abbott and the Roche SARS-CoV-2 antibody assays, but the Roche assay may be slightly more sensitive for patients tested within 0-6 days after first positive RT-PCR of SARS-CoV-2.