Karon, Brad S.

Objective. To evaluate the effectiveness of transcutaneous bilirubin (TcB) measurement in predicting risk for neonatal hyperbilirubinemia in outpatients. Design. Subjects were infants ≤8 days old seen in an outpatient clinic. Infants discharged with high-risk (HR) or high-intermediate risk (HIR) total serum bilirubin (TSB) values and jaundiced infants were recruited. TSB and TcB (BiliChek) levels were plotted on an hour-specific nomogram to determine risk for hyperbilirubinemia. Results. A total of 79 infants provided 87 sets of TcB and TsB values. Mean bias and standard deviation between TcB and TsB was 1.5 ± 2.1 mg/dL for outpatients, compared with 2.7 ± 1.3 mg/dL for inpatients. The sensitivity and specificity of HR or HIR TcB for predicting an HR or HIR TSB were 87% and 58%, respectively. Of 9 infants readmitted for phototherapy, 1 had a low-risk TcB and high-risk TSB. Conclusions. TcB screening in the outpatient environment may not be safe and efficient.

AbstractBackground: Glucose meter analytical performance criteria required for safe and effective management of patients on tight glycemic control (TGC) are not currently defined. We used simulation modeling to relate glucose meter performance characteristics to insulin dosing errors during TGC.Methods: We used 29 920 glucose values from patients on TGC at 1 institution to represent the expected distribution of glucose values during TGC, and we used 2 different simulation models to relate glucose meter analytical performance to insulin dosing error using these 29 920 initial glucose values and assuming 10%, 15%, or 20% total allowable error (TEa) criteria.Results: One-category insulin dosing errors were common under all error conditions. Two-category insulin dosing errors occurred more frequently when either 20% or 15% TEa was assumed compared with 10% total error. Dosing errors of 3 or more categories, those most likely to result in hypoglycemia and thus patient harm, occurred infrequently under all error conditions with the exception of 20% TEa.Conclusions: Glucose meter technologies that operate within a 15% total allowable error tolerance are unlikely to produce large (≥3-category) insulin dosing errors during TGC. Increasing performance to 10% TEa should reduce the frequency of 2-category insulin dosing errors, although additional studies are necessary to determine the clinical impact of such errors during TGC. Current criteria that allow 20% total allowable error in glucose meters may not be optimal for patient management during TGC.

Background: Previous studies have found positive bias and frequent outliers when central venous catheter (CVC) whole blood is used to dose glucose meters. We designed a study to determine whether positive bias and outliers with CVC whole blood glucose samples are due to exogenous glucose contamination of CVC samples, inherent bias and imprecision of glucose meters, or properties of CVC whole blood that interfere with the function of some glucose meters. Methods: We studied the relationship between venous whole blood and venous plasma glucose drawn by venipuncture to CVC whole blood and CVC plasma glucose in 50 hospitalized patients. In 27 patients whole blood glucose was measured on both the Accu-Chek ® Inform (Roche Diagnostics, Indianapolis, IN) and StatStrip™ (Nova Biomedical, Waltham, MA). Results: By comparing CVC plasma to venous plasma glucose, we determined that contamination of CVC samples with exogenous glucose was uncommon. On the Inform meter outliers were approximately twice as common with CVC whole blood compared to venous whole blood. In 27 patients who had CVC whole blood analyzed by both Inform and StatStrip, outliers occurred approximately twice as often on the Inform compared to the StatStrip. Accounting for CVC samples contaminated with exogenous glucose, outliers on the StatStrip did not occur significantly more often using CVC whole blood compared to venous whole blood. Conclusions: Properties unique to CVC whole blood differentially affect glucose meter bias and imprecision. Device selection is critical in practices that wish to use CVC whole blood to monitor glucose concentration in hospitalized patients.

Abstract We compared the clinical concordance of estimated glomerular filtration rate (eGFR) based on 3 whole blood creatinine assays with the eGFR calculated from a reference plasma creatinine assay. Whole blood creatinine on the Radiometer ABL800 FLEX (Radiometer A/S, Bronshoj, Denmark) demonstrated the best correlation and concordance to plasma creatinine/eGFR compared with the i-STAT (i-STAT, East Windsor, NJ) and StatSensor (Nova Biomedical, Waltham, MA). The i-STAT had better sensitivity (compared with Radiometer) but poorer specificity for prediction of plasma eGFR less than 60 mL/min/1.73 m2. The StatSensor demonstrated lower concordance of whole blood to plasma eGFR but offered a slope and an intercept offset feature that partially compensates for this effect. The optimal device for use in rapid determination of eGFR from whole blood creatinine may depend on whether it is more important in a given practice to optimize sensitivity, specificity, or overall concordance for determining plasma eGFR less than 60 mL/min/1.73 m2.

Abstract Background: Enzymatic creatinine assays are routinely used in clinical laboratories to provide more accurate estimated glomerular filtration rates and to avoid a perceived lack of analytical specificity associated with picrate (Jaffe) methods. Negative interferences with the enzymatic creatinine assay, which we noted in several patients on dopamine or dobutamine, prompted our further investigation into interference of catecholamines with enzymatic methods. Methods: Spiked solutions of dopamine, dobutamine, epinephrine, and norepinephrine were added to pooled sera at catecholamine concentrations consistent with clinically relevant dosing. Creatinine was measured enzymatically on the Roche P-Modular, Ortho Clinical Diagnostics Vitros 350, and Abbott i-STAT. Jaffe methods were performed on the Roche P-Modular and Siemens Dimension RxL. In 10 patients receiving dopamine and/or dobutamine via a venous or arterial line we evaluated and compared the extent of in vivo creatinine interference in paired serum samples obtained by venipuncture and from indwelling catheters. Results: All catecholamines caused significant negative interference with the Roche enzymatic creatinine assay, most pronounced for dopamine and dobutamine. The Vitros enzymatic assay demonstrated slight negative interferences, and i-STAT enzymatic and Jaffe methods were unaffected by the presence of catecholamines. Significant (P < 0.001) differences in creatinine concentrations by Roche enzymatic vs Jaffe methods were observed in venipuncture specimens compared with arterial or venous catheter specimens, suggesting dopamine and dobutamine reversibly adhere to the catheter lumen. Conclusions: Negative interferences were pronounced for Roche enzymatic results in blood samples obtained from indwelling catheters, a phenomenon not observed in peripheral draws. Physicians and laboratorians should be alert to the possibility of a falsely low creatinine result and reevaluate questionable samples using a method unaffected by catecholamines.

Abstract Background: We evaluated the sensitivity, precision, and concordance of 4 assays designed to detect aspirin responsiveness or resistance. Methods: Twenty-nine healthy laboratory volunteers took 80 mg aspirin for 7 days, and a subset of volunteers took 325 mg aspirin for an additional 7 days. We measured platelet function by light transmission aggregometry with arachidonic acid, PFA-100, and VerifyNow. PFA-100 and VerifyNow assays were performed in duplicate to assess method imprecision. Some volunteers had samples taken within 2–4 h of the final dose of aspirin and again within 20–24 h of the final dose. We measured urinary 11-dehydro-thromboxane B2 at baseline and after 80 or 325 mg aspirin. Results: No volunteers were nonresponsive to aspirin therapy as measured by the PFA-100. One of 29 participants demonstrated lack of response to aspirin as measured by VerifyNow and urinary 11-dehydro-thromboxane B2; 2 of 29 demonstrated lack of response as measured by light transmission aggregometry. Imprecision was <10% for the PFA-100 and VerifyNow. Concordance was high (>90%) between all assays. Neither aspirin dose (80 vs 325 mg) nor timing between final dose of aspirin and blood draw (2–4 vs 20–24 h) affected any of the assays. Conclusions: Light transmission aggregometry, PFA-100, VerifyNow, and urinary 11-dehydro-thromboxane B2 are all sensitive to the effects of aspirin in healthy individuals. Variables such as aspirin dose, timing between final dose of aspirin and blood collection, and imprecision do not affect the ability of the assays to detect aspirin effect on platelet function.

OBJECTIVE—Current criteria for the diagnosis of diabetic ketoacidosis (DKA) are limited by their nonspecificity (serum bicarbonate [HCO3] and pH) and qualitative nature (the presence of ketonemia/ketonuria). The present study was undertaken to determine whether quantitative measurement of a ketone body anion could be used to diagnose DKA. RESEARCH DESIGN AND METHODS—A retrospective review of records from hospitalized diabetic patients was undertaken to determine the concentration of serum β-hydroxybutyrate (βOHB) that corresponds to a HCO3 level of 18 mEq/l, the threshold value for diagnosis in recently published consensus criteria. Simultaneous admission βOHB and HCO3 values were recorded from 466 encounters, 129 in children and 337 in adults. RESULTS—A HCO3 level of 18 mEq/l corresponded with βOHB levels of 3.0 and 3.8 mmol/l in children and adults, respectively. With the use of these threshold βOHB values to define DKA, there was substantial discordance (∼≥20%) between βOHB and conventional diagnostic criteria using HCO3, pH, and glucose. In patients with DKA, there was no correlation between HCO3 and glucose levels on admission and a significant but weak correlation between βOHB and glucose levels (P < 0.001). CONCLUSIONS—Where available, serum βOHB levels ≥3.0 and ≥3.8 mmol/l in children and adults, respectively, in the presence of uncontrolled diabetes can be used to diagnose DKA and may be superior to the serum HCO3 level for that purpose. The marked variability in the relationship between βOHB and HCO3 is probably due to the presence of other acid-base disturbances, especially hyperchloremic, nonanion gap acidosis.