Heparin Concentration in Evacuated Tubes and Its Effect on pH, Ionized Calcium, Lactate, and Potassium in Venous Blood Gas Analysis.

Arterial blood specimens collected in evacuated tubes are unacceptable for blood gas analysis. However, evacuated tubes are routinely used for venous blood-gas analysis. The impact of the blood to heparin ratio on venous blood in evacuated tubes is unclear. Venous blood was drawn into lithium and sodium heparin evacuated tubes that were 1/3 full, ½ full, 2/3 full, and fully filled. Specimens were analyzed for pH, ionized calcium (iCa), lactate, and potassium on a blood-gas analyzer. The results for specimens filled only 1/3 full for lithium and sodium heparin tubes revealed a significant increase in pH and a significant decrease in the iCa. Underfilling the lithium and sodium heparin evacuated tubes did not significantly impact the lactate or potassium results. Venous whole-blood specimens should be filled to at least 2/3 full for accurate pH and iCa results.

New Diagnostic Cutoffs for Adrenal Insufficiency After Cosyntropin Stimulation Using Abbott Architect Cortisol Immunoassay.

INTRODUCTION: The accurate interpretation of the cosyntropin (adrenocorticotropic hormone [ACTH]) stimulation test requires method- and assay-specific cutoffs of the level of cortisol. Compared with a historical cutoff (18 µg/dL) for polyclonal antibody-based immunoassays, lower thresholds were proposed for the Roche Elecsys II assay, which uses a monoclonal antibody. However, cutoffs for other commonly adopted, monoclonal antibody-based cortisol assays were not yet available. Here, we established the thresholds for the level of cortisol specific to the Abbott Architect immunoassay by comparing the measurements of the level of cortisol using 3 immunoassays. METHODS: The ACTH stimulation test was performed in patients with suspected adrenal insufficiency (n = 50). The serum cortisol level was measured using the Abbott Architect, Roche Elecsys II, and Siemens Centaur assays. The results of the Abbott assay were also compared with those of liquid chromatography-tandem mass spectrometry. The receiver operating characteristic analysis was performed to derive new diagnostic thresholds for the Abbott assay using the polyclonal antibody-based Siemens assay as the reference method. RESULTS: The concentrations of cortisol measured using the Abbott assay were similar to those measured using liquid chromatography-tandem mass spectrometry and the Roche Elecsys II assay but significantly lower than those measured using the Siemens assay. The optimized threshold for cortisol using the Abbott assay was 14.6 µg/dL at 60 minutes after stimulation (sensitivity, 92%; specificity, 96%) and 13.2 µg/dL at 30 minutes after stimulation (sensitivity, 100%; specificity, 89%). CONCLUSION: We recommend a threshold of 14.6 µg/dL for the level of cortisol at 60 minutes after ACTH stimulation for the Abbott assay. In comparison with the historical threshold of 18 µg/dL, the application of the new cutoff may significantly decrease false-positive results due to ACTH stimulation testing. The use of assay-specific cutoffs will be essential for reducing misclassification and overtreatment in patients with suspected adrenal insufficiency.

Evaluation of the Preanalytical Interference of Hemoglobin, Bilirubin, or Lipids in Therapeutic Drug Monitoring Assays on Beckman Coulter AU Analyzers.

OBJECTIVE: The aim of this study was to evaluate the influence of hemolysis, icterus, and lipemia (HIL) interferences on 8 therapeutic drug monitoring (TDM) assays. METHODS: Amikacin, carbamazepine, digoxin, lidocaine, lithium, methotrexate, phenobarbital, and theophylline were spiked in specimen pools at the clinical decision cutoff values. The interferents were spiked in vitro in specimen pools. All analytes were tested on Beckman Coulter AU analyzers. RESULTS: Hemolysis interference was detected in quantitative microsphere system (QMS) amikacin at 55.59 µg/mL at a concentration of 500 mg/dL hemoglobin. Icterus interference was detected in enzyme multiplied immunoassay technique amikacin at 43.62 µg/mL and in QMS amikacin at 55.59 µg/mL, at a concentration of 20 mg/dL bilirubin. CONCLUSION: Although the reference range value is recommended for clinical significance bias assessment for HIL interferences on most chemistry assays, an important investigation of the HIL interferences on TDM assays is to establish interferent thresholds at the clinical critical cutoff values.