N-acetylcysteine interference of Trinder-based assays.

OBJECTIVES: The primary objective of this study was to evaluate potential interference of Trinder-based chemistry assays by N-acetylcysteine (NAC). A secondary objective was to look for evidence of interference in patients treated with NAC for acetaminophen (APAP) overdose. DESIGN AND METHODS: Dilutions of NAC in plasma were tested for interference using the following Roche Diagnostics Trinder-based assays on a cobas 8000 system: enzymatic creatinine (Cr), cholesterol (CHOL), high-density lipoprotein cholesterol (HDL-C), triglycerides (TRIG), and uric acid (UA). Two non-Trinder Roche assays - urea nitrogen (BUN) and glucose (GLUC) - were tested as controls. Sekisui N-geneous® low-density lipoprotein cholesterol (LDL-C) reagent was also evaluated. Retrospective chart review of APAP overdose cases over 49months was conducted to look for differences in plasma Cr before and after intravenous (IV) NAC administration. RESULTS: NAC concentrations (shown in parentheses) that caused ≥10% inhibition for individual assays were (in order of sensitivity to interference): TRIG (570mg/L)>CHOL (740mg/L)≈Cr (790mg/L)>UA (1100mg/L)>HDL-C (1760mg/L)>LDL-C (2900mg/L). Neither BUN nor GLUC achieved significant inhibition up to 10,000mg/L NAC. Evidence for relatively minor inhibition of Cr was observed in patients after NAC administration. CONCLUSIONS: NAC inhibition of the assays investigated typically occurs at concentrations higher than expected during IV and oral NAC therapy.

Effect of specimen type on free immunoglobulin light chains analysis on the Roche Diagnostics cobas 8000 analyzer.

The measurement of free immunoglobulin light chains is typically performed on serum; however, the use of alternative specimen types has potential benefits. Using the Freelite™ kappa and lambda free light chains assay on a Roche Diagnostics cobas 8000 c502 analyzer, we compared three specimen types (serum, EDTA-plasma and lithium heparin plasma separator gel-plasma) on 100 patients. Using Deming regression and eliminating outliers (limiting data to light chain concentrations below 400 mg/L), the three specimen types showed comparable results for kappa light chain concentration, lambda light chain concentration, and kappa/lambda ratio with slopes close to 1.0 and y-intercepts close to zero. EDTA-plasma showed slightly more positive bias relative to serum than lithium heparin. Analysis using EDTA-plasma and lithium heparin plasma showed comparable linearity, precision, and temperature stability. A single sample showing hook effect (not in the comparison set) gave comparable results using either plasma specimen type. For the Freelite™ kappa and lambda free light chains assay, both EDTA-plasma or lithium heparin-plasma can serve as acceptable substitutes for serum, at least for the Roche cobas 8000 analyzer.

Impact of add-on laboratory testing at an academic medical center: a five year retrospective study.

BACKGROUND: Clinical laboratories frequently receive orders to perform additional tests on existing specimens ('add-ons'). Previous studies have examined add-on ordering patterns over short periods of time. The objective of this study was to analyze add-on ordering patterns over an extended time period. We also analyzed the impact of a robotic specimen archival/retrieval system on add-on testing procedure and manual effort. METHODS: In this retrospective study at an academic medical center, electronic health records from were searched to obtain all add-on orders that were placed in the time period of May 2, 2009 to December 31, 2014. RESULTS: During the time period of retrospective study, 880,359 add-on tests were ordered on 96,244 different patients. Add-on testing comprised 3.3 % of total test volumes. There were 443,411 unique ordering instances, leading to an average of 1.99 add-on tests per instance. Some patients had multiple episodes of add-on test orders at different points in time, leading to an average of 9.15 add-on tests per patient. The majority of add-on orders were for chemistry tests (78.8 % of total add-ons) with the next most frequent being hematology and coagulation tests (11.2 % of total add-ons). Inpatient orders accounted for 66.8 % of total add-on orders, while the emergency department and outpatient clinics had 14.8 % and 18.4 % of total add-on orders, respectively. The majority of add-ons were placed within 8 hours (87.3 %) and nearly all by 24 hours (96.8 %). Nearly 100 % of add-on orders within the emergency department were placed within 8 hours. The introduction of a robotic specimen archival/retrieval unit saved an average of 2.75 minutes of laboratory staff manual time per unique add-on order. This translates to 24.1 hours/day less manual effort in dealing with add-on orders. CONCLUSION: Our study reflects the previous literature in showing that add-on orders significantly impact the workload of the clinical laboratory. The majority of add-on orders are clinical chemistry tests, and most add-on orders occur within 24 hours of original specimen collection. Robotic specimen archival/retrieval units can reduce manual effort in the clinical laboratory associated with add-on orders.