Error simulation modeling to assess the effects of bias and precision on bilirubin measurements used to screen for neonatal hyperbilirubinemia.

OBJECTIVES: Error simulation models have been used to understand the relationship between analytical performance and clinical outcomes. We developed an error simulation model to understand the effects of method bias and precision on misclassification rate for neonatal hyperbilirubinemia using an age-adjusted risk assessment tool. METHODS: For each of 176 measured total bilirubin (TSBM) values, 10,000 simulated total bilirubin (TBS) values were generated at each combination of bias and precision conditions for coefficient of variation (CV) between 1 and 15%, and for biases between -51.3 µmol/L and 51.3 µmol/L (-3 and 3 mg/dL) fixed bias. TBS values were analyzed to determine if they were in the same risk zone as the TSBM value. We then calculated sensitivity and specificity for prediction of ≥75th percentile for postnatal age values as a function of assay bias and precision, and determined the rate of critical errors (≥95th percentile for age TSBM with <75th percentile TBS). RESULTS: A sensitivity >95% for predicting ≥75th percentile bilirubin values was observed when there is a positive fixed bias of greater than 17.1 µmol/L (1.0 mg/dL) and CV is maintained ≤10%. A specificity >70% for predicting <75th percentile bilirubin values was observed when positive systematic bias was 17.1 µmol/L (1 mg/dL) or less at CV ≤ 10%. Critical errors did not occur with a frequency >0.2% until negative bias was -17.1 µmol/L (-1 mg/dL) or lower. CONCLUSIONS: A positive systematic bias of 17.1 µmol/L (1 mg/dL) may be optimal for balancing sensitivity and specificity for predicting ≥75th percentile TSB values. Negative systematic bias should be avoided to allow detection of high risk infants and avoid critical classification errors.

Human chorionic gonadotropin suspected heterophile interference investigations in immunoassays: a recommended approach.

Background Heterophile antibody (HAb) interferences in immunoassays can cause falsely elevated hCG concentrations leading to incorrect diagnosis and treatments options. When results are not consistent with the clinical findings, hCG HAb interference investigation may be requested by the physician. A retrospective evaluation of the frequency of HAb interference was performed among cases of physician-requested investigations and the effectiveness of commercially available blocking reagents to detect HAb interference in two immunoassay systems was evaluated. Methods One hundred and thirteen physician requests for hCG HAb investigation from 2008 to 2017 were reviewed. The primary method used to measure hCG was the Beckman Coulter Access Total ßhCG (2008-2010) and the Roche Elecsys HCG+ß (2014-2017). HAb investigation included measurement by two immunoassays before and after treatment of samples with heterophile blocking reagents and serial dilution studies. Results Five cases of HAb and HAb-like interference were identified. The interference frequency was 6.7% for the Beckman assay and 2.9% for the Roche assay. The presence of HAb was detected using heterophile blocking reagents and an alternative method in three cases. The other two cases were detected due to discrepant results with an alternative method and non-linear serial dilutions (HAb-like). Conclusions HAb interference was observed in the Beckman and the Roche assays. The heterophile blocking reagents failed to detect 40% of interference cases. Blocking reagents should not solely be used for these investigations. Multiple strategies including the use of serial dilutions and using an alternative platform are critical when troubleshooting interferences in hCG immunoassays.

Implementation of a reformulated Roche® bilirubin Gen.3 reagent did not affect the relationship between BiliChek transcutaneous and Roche total serum bilirubin.

OBJECTIVE: Determine whether introduction of a reformulated bilirubin reagent, the Roche bilirubin Gen.3 assay, changed the relationship between BiliChek transcutaneous bilirubin (TcB) and total serum bilirubin (TSB). DESIGN AND METHODS: TcB results from term infants in the level 1 nursery obtained within one hour of a TSB were reviewed over two periods, six months before and after the conversion from the previous generation Roche bilirubin reagent to the new Roche Gen.3 bilirubin assay. TcB measurements were performed using BiliChek transcutaneous devices (Respironics, Marietta GA). Distribution of TSB results, and TcB minus TSB bias, were compared before and after introduction of the reformulated Roche bilirubin Gen.3 assay. Median and interquartile range (IQR) TSB values and bias were calculated. A statistical difference between median TSB values and bias were assessed using Man-Whitney test. RESULTS: A total of 301 paired TcB and TSB results were obtained, 172 before and 129 after implementation of the reformulated Roche bilirubin Gen.3 reagent. Median (IQR) TSB was 7.8 (6.8-8.7)mg/dL (133.3 (116.3-148.8) µmol/L) before and 7.6 (6.7-8.4)mg/dL (130 (114.6-143.6)µmol/L) after implementation of the reformulated reagent (p = .1373). Median (IQR) bias between TcB and TSB was 2.9 (2.2-3.7) mg/dL (49.6 (37.6-63.3)µmol/L) before the reformulated reagent was implemented; and did not change at 2.9 (2.1-3.9) mg/dL (49.6 (35.9-66.7)µmol/L) after implementation (p = .8242). CONCLUSION: Implementation of the reformulated Roche bilirubin Gen.3 reagent did not affect the relationship between BiliChek transcutaneous and total serum bilirubin; thus no changes were needed to the neonatal TcB screening protocol as a result of the new bilirubin reagent.

Blood gas sample spiking with total parenteral nutrition, lipid emulsion, and concentrated dextrose solutions as a model for predicting sample contamination based on glucose result.

OBJECTIVE: Evaluate the effects of blood gas sample contamination with total parenteral nutrition (TPN)/lipid emulsion and dextrose 50% (D50) solutions on blood gas and electrolyte measurement; and determine whether glucose concentration can predict blood gas sample contamination with TPN/lipid emulsion or D50. DESIGN AND METHODS: Residual lithium heparin arterial blood gas samples were spiked with TPN/lipid emulsion (0 to 15%) and D50 solutions (0 to 2.5%). Blood gas (pH, pCO2, pO2), electrolytes (Na+, K+ ionized calcium) and hemoglobin were measured with a Radiometer ABL90. Glucose concentration was measured in separated plasma by Roche Cobas c501. Chart review of neonatal blood gas results with glucose >300 mg/dL (>16.65 mmol/L) over a seven month period was performed to determine whether repeat (within 4 h) blood gas results suggested pre-analytical errors in blood gas results. Results were used to determine whether a glucose threshold could predict contamination resulting in blood gas and electrolyte results with greater than laboratory-defined allowable error. RESULTS: Samples spiked with 5% or more TPN/lipid emulsion solution or 1% D50 showed glucose concentration >500 mg/dL (>27.75 mmol/L) and produced blood gas (pH, pO2, pCO2) results with greater than laboratory-defined allowable error. TPN/lipid emulsion, but not D50, produced greater than allowable error in electrolyte (Na+,K+,Ca++,Hb) results at these concentrations. Based on chart review of 144 neonatal blood gas results with glucose >250 mg/dL received over seven months, four of ten neonatal intensive care unit (NICU) patients with glucose results >500 mg/dL and repeat blood gas results within 4 h had results highly suggestive of pre-analytical error. Only 3 of 36 NICU patients with glucose results 300-500 mg/dL and repeat blood gas results within 4 h had clear pre-analytical errors in blood gas results. CONCLUSION: Glucose concentration can be used as an indicator of significant blood sample contamination with either TPN/lipid emulsion or D50 solution. NICU blood gas samples with glucose ≥300 mg/dL should be considered potentially contaminated, and samples with glucose >500 mg/dL have a risk for contamination.