Evaluation of the In Vitro Interference of Hemoglobin, Lipids, and Bilirubin on the Measurement of Plasma Advanced Oxidation Protein Products.

BACKGROUND: The pre-analytical phase is the most vulnerable and contributes to the majority of errors in laboratory assays. Therefore, the aim of this study was to evaluate in vitro interference of hemoglobin, lipids, and bilirubin on measurement of plasma advanced oxidation protein products (AOPPs). METHODS: AOPPs were measured in a sample spiked with increasing concentrations of hemoglobin, Intralipid® 20% or bilirubin. Then, the relative deviation of the result from the nonspiked baseline value was calculated. RESULTS: We found that all interferents analyzed influenced AOPPs baseline value significantly. Hemoglobin produced a non-linear negative bias, with a maximum decrease of 21.1%. Otherwise, lipids and bilirubin produced a positive bias, ranging from 20.0 to 90.9%, and 12.1 to 33.2%, respectively. CONCLUSIONS: The addition of interferents produced a significant bias in the measurement of AOPPs and in different degrees at the majority of concentrations added.

Prognostic value of red blood cell distribution width in prediction of in-hospital mortality in patients with acute myocardial infarction.

BACKGROUND: Red blood cell indices may add important prognostic information to risk stratification scores, such as Global Registry of Acute Coronary Events (GRACE) risk score. However, the incremental predictive value of red blood cell distribution width (RDW) on this score has not been assessed. Therefore, the aim of this study was to assess whether the RDW has additional prognostic value on the GRACE risk score in prediction of in-hospital mortality in patients with acute myocardial infarction (AMI). METHODS: A historic cohort was investigated at the University Hospital in Santa Maria city, Brazil. The laboratory database and medical registry were used to identify patients with AMI. A total of 109 patients were eligible for the present study. Cox regression models were calculated including GRACE risk score variables plus RDW. Moreover, measures of discrimination and calibration were also calculated. The primary outcome evaluated was all-cause in-hospital mortality. RESULTS: When included in a predictive model based on the GRACE risk score, RDW became an independent predictor of in-hospital mortality (HR 1.358, 95% CI 1.04 - 1.77; p = 0.023). The addition of RDW to the original model showed adequate calibration (Hosmer-Lemeshow p-value 0.174) and produced a slight improvement in its discriminatory power (AUC 0.769, 95% CI 0.677 - 0.847; p = < 0.0001). CONCLUSIONS: We suggest that RDW might provide additional information over the GRACE risk score in patients with AMI.

Evaluation of the in vitro interference of bilirubin and lipids in the measurement of the plasma glutathione reductase activity.

BACKGROUND: The pre-analytical phase is the most vulnerable to errors, and some of the most common interferents in laboratory routine are bilirubin and lipemia. Therefore, the aim of this study was to evaluate the in vitro interference of bilirubin and lipids in the measurement of the activity of glutathione reductase (GR) in plasma samples. METHODS: The evaluation of the in vitro interference of bilirubin was performed by addition of bilirubin to a plasma pool at the following final concentrations: 0.9, 1.9, 3.8, 7.5, 15, and 30 mg/dL. The turbidity of lipemia was simulated by the addition of Intralipid to the plasma pool at the following final concentrations: 0.67, 1.25, 2.5, 5, and 10 mg/dL. GR activity was measured on a Cobas MIRA automated analyzer. RESULTS: Plasma GR activity was significantly affected by bilirubin and lipids. At the concentrations of 0.9 to 30 mg/dL of bilirubin added, the decrease of GR activity ranged between 22.9 to 45.4%. At the concentrations of 0.67 to 10 mg/dL of Intralipid added, the decrease of GR activity ranged between 22.4 to 36.5%. CONCLUSIONS: The addition of bilirubin and lipids in plasma samples interferes negatively in the measurement of GR activity, since GR values are reduced in the presence of these in vitro interferents.