Accuracy-Based Vitamin D Survey: Six Years of Quality Improvement Guided by Proficiency Testing

CONTEXT.—

The goal of the College of American Pathologists Accuracy-Based Proficiency Testing Program is to promote the quality, standardization, and harmonization of clinical laboratory results through proficiency testing specimens that are free from matrix effects, have target values that are traceable to reference methods, and that probe the limitations of current methods.

OBJECTIVE.—

To summarize the first 6 years of the Accuracy-Based Vitamin D Survey and highlight key insights from the data generated as it relates to assay performance.

DESIGN.—

Accuracy-based challenges were created by using pooled human serum samples. Certain samples were derived from participants in an institutional review board-approved protocol in which vitamin D-deficient participants were treated with ergocalciferol (vitamin D₂). Reference targets for the survey were set by the Centers for Disease Control and Prevention using isotope-dilution liquid chromatography-tandem mass spectrometry. Each method was compared with the reference method procedure over the course of the program (n = 43 proficiency testing samples).

RESULTS.—

Linear regression versus the reference method procedure revealed proportional biases across the methods, ranging from 0.0% to 16.7%. Pearson correlation coefficients (r²) ranged from 0.902 to 0.996. Results were influenced by the concentration of 25-hydroxyvitamin D₂ as well as the C-3 epimer of 25-hydroxyvitamin D₃. During the 6 years, 2 manufacturers altered their assays to match the reference method procedure more closely.

CONCLUSIONS.—

There is considerable bias, both proportional bias and sample-specific matrix effects, affecting many assays. This ongoing accuracy-based proficiency testing program for vitamin D will provide the data needed for laboratories and manufacturers to improve their assays and thereby patient care.

Multilectin Affinity Chromatography for Characterization of Multiple Glycoprotein Biomarker Candidates in Serum from Breast Cancer Patients

Background: Glycoproteins are often associated with cancer and are important in serum studies, for which glycosylation is a common posttranslational modification.

Methods: We used multilectin affinity chromatography (M-LAC) to isolate glycoproteins from the sera of breast cancer patients and controls. The proteins were identified by HPLC–tandem mass spectrometry (MS/MS) analysis of the corresponding tryptic digests. We used the FuncAssociate Gene Ontology program for association analysis of the identified proteins. Biomarker candidates in these groups were comparatively quantitated by use of peak area measurements, with inclusion of an internal standard. We analyzed data for concordance within the ontology association groups for vector of change with the development of breast cancer.

Results: Detection of the known low-concentration biomarker HER-2 (8–24 μg/L) enabled us to establish a dynamic range of 106, relative to the amount of albumin, for the depletion step. We then used ELISA to confirm this range. Proteins associated with lipid transport and metabolism, cell growth and maintenance, ion homeostasis, and protease inhibition were found to be differentially regulated in serum from women with breast cancer compared with serum from women without breast cancer.

Conclusions: M-LAC for isolation of the serum glycoproteome, coupled with liquid chromatography–MS/MS and the use of gene ontology associations, can be used to characterize large panels of candidate markers, which can then be evaluated in a particular patient population.

Total Long-term Within-Laboratory Precision of Cortisol, Ferritin, Thyroxine, Free Thyroxine, and Thyroid-Stimulating Hormone Assays Based on a College of American Pathologists Fresh Frozen Serum Study: Do Available Methods Meet Medical Needs for Precision?

Context.—It is important that the total long-term precision of laboratory methods meet the medical needs of the patients being served.

Objectives.—To determine the long-term within- and between-laboratory variation of cortisol, ferritin, thyroxine, free thyroxine, and thyroid-stimulating hormone measurements using commonly available methods and to determine if these variations are within accepted medical needs.

Design.—Two vials of pooled frozen serum were mailed 6 months apart to laboratories participating in 2 separate College of American Pathologists surveys. The data from those laboratories that analyzed an analyte in both surveys were used to determine for each method the total variance and the within- and between-laboratory components.

Setting.—The study included the A mailing of the 2003 College of American Pathologists Ligand Survey and the C mailing of the Chemistry Survey.

Main Outcome Measures.—For each analyte, total variance was partitioned into within- and between-laboratory components for each analytic method. The within-laboratory variations were then compared with imprecision criteria based on biological variation.

Participants.—The laboratories that reported results on the same analyte using the same method in both surveys.

Results.—For each analyte, the median of the long-term within-laboratory variances of each peer group was 78% to 95% of its total-survey variance, and the median long-term within-laboratory coefficients of variation varied from 5.1% to 7.6%. The number of methods that met within-laboratory imprecision goals based on biological criteria were 5 of 5 for cortisol; 5 of 7 for ferritin; 0 of 7 for thyroxine and free thyroxine; and 8 of 8 for thyroid-stimulating hormone.

Conclusions.—For all analytes tested, the total within-laboratory component of variance was the major source of variability in this study. In addition, there are several methods, especially for thyroxine and free thyroxine, that may not meet analytic goals in terms of their imprecision.

Chorea as a paraneoplastic complication of Hodgkin's disease

Neurologic complications of Hodgkin's disease (HD) include both metastatic and non-metastatic involvement of the nervous system. There are at least five paraneoplastic syndromes associated with HD but chorea has not been described. We report the first choreiform disorder as a paraneoplastic complication of HD and only the second case of paraneoplastic chorea in the literature.