Study guide on serum 25-hydroxycalciferol assay harmonization study

RESEARCH ARTICLE

• Title: Harmonization of serum 25-hydroxycalciferol assay results from high-performance liquid chromatography, enzyme immunoassay, radioimmunoassay, and immunochemiluminescence systems: A multicenter study

• Authors: Bahareh Nikooyeh, Siamak M. Samiee, Marjan R. Farzami, Hamid Alavimajd, Maliheh Zahedirad, Ali Kalayi, Nastaran Shariatzadeh, Nasrin Boroumand, Elham Golshekan, Yalda Gholamian, Tirang R. Neyestani

• Affiliations:

  • Laboratory of Nutrition Research, National Nutrition and Food Technology Research Institute, Faculty of Nutrition Sciences and Food Technology, Shahid Beheshti University of Medical Sciences, Tehran, Iran

  • Health Reference Laboratories (HRL), Iran Ministry of Health

  • Department of Biostatistics, Faculty of Paramedicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran

• Correspondence: Tirang R. Neyestani; Contact via email.

BACKGROUND

• **Issue at Hand: **

  • Remarkable disagreement among different systems assessing serum 25-hydroxy vitamin D (25(OH)D) complicates decision-making for clinical and community interventions.

• Objective:

  • This study aims to harmonize results obtained from different 25(OH)D assay systems, analyzing overall agreement.

METHODS

• Sample Collection:

  • A total of 275 serum samples analyzed.

  • Samples underwent testing through various methods:

  • DIAsource-enzyme immunoassay (EIA)

  • DIAsource-radioimmunoassay (RIA)

  • Roche-electrochemiluminescence (ECL)

  • Diasorin-chemiluminescent immunoassay (CLIA)

  • High-performance liquid chromatography (HPLC) used as the reference method.

  • Serum intact parathyroid hormone (iPTH) levels were also measured in all samples.

• Data Analysis:

  • Between-system agreement and harmonization evaluated using:

  • Bland-Altman analysis

  • Receiver operating characteristic (ROC) analysis

  • Regression analysis

RESULTS

• **Findings: **

  • Mean serum 25(OH)D concentrations showed significant differences across systems (P<.001).

  • Correlation with HPLC results:

  • ECL: Positive bias of +3.8 nmol/L

  • CLIA: Negative bias of −11.9 nmol/L

  • EIA: Positive bias of 8.0 nmol/L

  • RIA: Positive bias of 8.1 nmol/L

  • When system-specific cutoffs were defined based on HPLC results, the mean 25(OH)D results were more harmonized.

STATISTICAL EVALUATION

• Statistical Methods:

  • Measures of central tendency (mean ± SD) and frequency distributions were reported.

  • Calculated sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and correlations (Pearson’s/Spearman’s).

• Statistical Significance:

  • Significant findings were deemed at P<.05.

DISCUSSION

• Implications:

  • Improvements in harmonizing assay results enhance clinical follow-up and comparisons at national/international levels.

  • Addressing variable testing results is essential for accurate health assessments related to vitamin D.

• Clinical Relevance of Vitamin D:

  • Vitamin D's role extends beyond bone health; implicated in various health disorders.

• Cutoff Definition:

  • Cutoff points proposed based on iPTH concentrations, allowing for accurate classification of vitamin D deficiency versus sufficiency.

CONCLUSIONS

• Conclusion:

  • Adjusting circulating 25(OH)D concentrations based on HPLC resulted in harmonized frequency distribution of vitamin D status.

ABBREVIATIONS

• Common Abbreviations Used:

  • AUC: Area Under the ROC Curve

  • CI: Confidence Interval

  • CLIA: Chemiluminescent Immunoassay

  • ECL: Electrochemiluminescence

  • EIA: Enzyme Immunoassay

  • HPLC: High-Performance Liquid Chromatography

  • iPTH: Intact Parathyroid Hormone

  • RIA: Radioimmunoassay

• Any new definitions or methods introduced from the research are also synthesized in context to the prominent key findings.

REFERENCE CITATION

• Nikooyeh B, Samiee SM, Farzami MR, et al. Harmonization of serum 25-hydroxycalciferol assay results from high-performance liquid chromatography, enzyme immunoassay, radioimmunoassay, and immunochemiluminescence systems: A multicenter study. J Clin Lab Anal. 2017;31:e22117. DOI: 10.1002/jcla.22117.

BACKGROUND

• The Vitamin D Measurement Gap: There is a significant lack of agreement among various laboratory systems used to measure serum 25-hydroxy vitamin D (25(OH)D). This discrepancy makes it difficult for clinicians to apply universal health guidelines and for public health officials to monitor population-level deficiency.

• Objective of the Study: To evaluate the level of agreement between four common commercial assay systems and a reference method (HPLC), and to develop strategy for harmonization to ensure more consistent clinical decision-making.

DETAILED METHODS

• Sample Population: 275 serum samples were collected and analyzed to assess 25(OH)D levels across various platforms.

• Assay Systems Evaluated:

  • DIAsource-enzyme immunoassay (EIA): A method utilizing enzymatic reactions for detection.

  • DIAsource-radioimmunoassay (RIA): A competitive binding assay using radiolabeled isotopes.

  • Roche-electrochemiluminescence (ECL): An automated system based on light emission via electrochemical reactions.

  • Diasorin-chemiluminescent immunoassay (CLIA): A detection method using chemical reagents to produce light.

• Reference Standard: High-performance liquid chromatography (HPLC) was utilized as the gold standard reference method for comparative accuracy.

• Secondary Biomarker: Serum intact parathyroid hormone (iPTH) levels were measured in all subjects to analyze the physiological response to varying Vitamin D concentrations.

• Sensitivity vs specificity means the ability of a test to correctly identify true positives (sensitivity) versus its ability to correctly identify true negatives (specificity), which is crucial in evaluating the performance of the serum 25-hydroxycalciferol assay.

RESULTS AND BIAS ANALYSIS

• Statistical Significance: The study found highly significant differences in mean serum 25(OH)D concentrations between the different testing platforms (P < .001).

• Performance Relative to HPLC:

  • ECL: Demonstrated a slight positive bias of +3.8 \text{ nmol/L}.

  • CLIA: Shown to have a significant negative bias of -11.9 \text{ nmol/L}, meaning it consistently underestimated Vitamin D levels.

  • EIA: Observed a notable positive bias of +8.0 \text{ nmol/L}.

  • RIA: Displayed a similar positive bias of +8.1 \text{ nmol/L}.

• The Effect of Harmonization: By applying system-specific cutoff points derived from the reference HPLC data, the researchers were able to achieve a significantly more uniform distribution of results across all platforms.

STATISTICAL EVALUATION

• Metrics Observed: The study utilized multiple statistical tools to ensure data integrity:

  • Central Tendency: Data reported as mean \pm standard deviation (SD).

  • Diagnostic Accuracy: Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated.

  • Correlation: Pearson’s or Spearman’s correlation coefficients were used depending on data distribution.

• Agreement Assessment: Bland-Altman plots were used to visualize the bias between methods, and Receiver Operating Characteristic (ROC) analysis was applied to evaluate the performance of different cutoff points.

• Significance Threshold: Results were considered statistically significant if P < .05.

DISCUSSION AND CLINICAL IMPLICATIONS

• Wide-Reaching Health Roles: Vitamin D is no longer viewed solely as a regulator of calcium and bone metabolism. It is now implicated in the pathogenesis of cardiovascular disease, certain cancers, and autoimmune disorders.

• Combating Misclassification: Variability in test results can lead to patients being incorrectly diagnosed as deficient (leading to unnecessary supplementation) or sufficient (missing the need for treatment).

• The iPTH Link: The study proposed defining cutoff points based on the concentration of iPTH. There is an inverse relationship where lower 25(OH)D levels lead to increased iPTH (secondary hyperparathyroidism). Identifying the 25(OH)D level where iPTH begins to rise provides a functional threshold for deficiency.

CONCLUSIONS

• Summary: The study proves that laboratory results for 25(OH)D are currently not interchangeable. However, adjusting circulating concentrations based on a reference standard like HPLC allows for a harmonized frequency distribution, which is essential for accurate national and international comparisons of Vitamin D status.

ABBREVIATIONS

• AUC: Area Under the ROC Curve

• CI: Confidence Interval

• CLIA: Chemiluminescent Immunoassay

• ECL: Electrochemiluminescence

• EIA: Enzyme Immunoassay

• HPLC: High-Performance Liquid Chromatography

• iPTH: Intact Parathyroid Hormone

• RIA: Radioimmunoassay