Reducing Specimen Rejection Rates Using Concentration-Dependent Hemolysis Rejection Thresholds.

BACKGROUND: Using middleware solutions, it is possible to implement concentration-dependent analyte-specific hemolysis rejection limits. This makes day-to-day reporting of clinical specimens more efficient and potentially lowers sample rejection rates compared to a "one-size-fits-all" approach (i.e., solely based on a single cutoff provided in the package insert). METHODS: Hemolysis interference studies were performed at multiple analyte concentrations for three frequently ordered tests. For each assay, concentration-dependent hemolysis rejection limits were designed based on the total allowable error (TAE) for the analyte as well as the clinical significance of such incurred inaccuracy at the respective concentrations. In general, the following rationale was used: if the interference exceeds 10% (or package insert cutoffs), a comment is placed on the result. If the interference exceeds the TAE, the result will not be reported. Reduction in specimen rejection rates were estimated by comparing the incurred specimen rejection rates when package inserts' vs concentration-dependent hemolysis interference limits were applied to a data set in our institute during a three-month period. RESULTS: Concentration-dependent analyte-specific hemolysis rejection thresholds were designed for three commonly ordered assays that are especially susceptible to hemolysis interference. It is estimated that these novel thresholds for aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and direct bilirubin (DBIL) reduced specimen rejection rates from 9.3% to 1.3%, 31.4% to 4.8%, and 19.9% to 7.1%, respectively. CONCLUSIONS: Concentration-dependent analyte-specific hemolysis rejection thresholds for three commonly ordered assays can reduce rejection rates without significantly compromising the quality of test results.

Evaluation of a New Generation Automated Assay for 25-Hydroxy Vitamin D Based on Competitive Protein Binding.

BACKGROUND: The interest for vitamin D has exponentially increased testing demand for 25-hydroxy vitamin D [25(OH)D]. Consequently, many laboratories are switching from LC-MS/MS methods to automated, high-throughput immunoassays. One of the major potential issues with these assays has been the lack of cross-reactivity with 25(OH)D2. METHODS: We have evaluated the Roche Elecsys vitamin D total II assay for accuracy by comparing 79 patient samples with LC-MS/MS. The cross-reactivity for 25(OH)D2 was evaluated by analyzing samples with high 25(OH)D2 separately and estimating 25(OH)D2 recovery, as well as by spiking of 25(OH)D2. The assay was further evaluated for precision, linearity, sample type, and common interferences. RESULTS: There was mostly good agreement between the Elecsys and LC-MS/MS assays (Deming regression: y = 0.95x + 0.70), with an overall bias of 2.3% (-0.84 ng/mL). However, there were 6 out of 79 (7.6%) discordant samples. The Deming regression for samples with high 25(OH)D2 compared to LC-MS/MS showed similar slope and intercept (y = 0.97x - 1.1). The average recovery of 25(OH)D2 for these samples was 90%. The initial precision studies were in general agreement with the package insert, but long-term clinical use showed higher-than-claimed imprecision (11.7%-14.4% at 12 ng/mL and 6.9%-7.6% at 27 ng/mL; claimed: 7.2% and 5.0%, respectively). We observed 1 falsely high result in plasma, an issue previously addressed by Roche in a medical device correction. CONCLUSIONS: The analytical performance of the Roche Vitamin D assay was acceptable, and the assay had a good cross-reactivity for 25(OH)D2.