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Icterus, a phenomenon caused by bilirubin elevation in the blood, is a common endogenous interference in chemistry testing, occurring either spectrally or through chemical reactivity with assay reagents. Often, laboratories have few options other than to dilute or reject samples exceeding icteric thresholds. However, recent studies have optimized in vitro photoisomerization of bilirubin to a 17-minute bilirubin half-life using 500 nm light at 37 °C. Using an enzymatic creatinine assay as a model, due to its prevalence in routine laboratory testing and susceptibility to icteric interference, our study explores the usage of in vitro photoisomerization by replicating these conditions in a device, the Bilibox, as means of resolving icterus in laboratory testing. Left-over icteric and non-icteric clinical samples, collected by lithium heparin vacutainer (n = 10), were analyzed for baseline creatinine, diluted creatinine (1:4 0.9 % NaCl), total bilirubin, direct bilirubin, and hemolysis, icterus and lipemia (HIL) indices. Samples were then placed in the Bilibox in two intervals of 30 min with repeat measurements of the aforementioned analytes. On average, icteric-index, total bilirubin (TBIL), and direct bilirubin (DBIL) decreased by 33.5, 39.1 and 39.9 % respectively following 30 min of Bilibox treatment; and by 47.6 %, 63.7 % and 59.8 % following 60 min. The average percent difference between the pre-exposure diluted and undiluted creatinine was 5.8 %, demonstrating the icterus interference. Following Bilibox treatment, the difference between undiluted (post-exposure) and diluted (pre-exposure) creatinine decreased to 0.02 % (p = 0.0232) and 2.2 % (p = 0.0021) at 30 and 60 min of treatment respectively, demonstrating resolution of interference. Consequently, photoisomerization can be utilized as an additional and reasonably quick method for resolving icterus when dilutional methods cannot be applied.

We compared two different methods of whole blood sodium measurement to plasma sodium measurement using samples in the profoundly hyponatremic range (Na120 mmol/L).Whole blood pools with a range of low sodium values were generated using combinations and dilutions of pooled electrolyte-balanced lithium heparin samples submitted for arterial blood gas analysis. Each pool was analyzed five times on a Radiometer 827 blood gas analyzer and iSTAT analyzer. Pools were centrifuged to produce plasma, which was analyzed five times on a Roche Cobas c501 chemistry analyzer. An additional 40 fresh (analyzed on day of collection) excess lithium heparin arterial blood gas samples from 36 patients were analyzed on the Radiometer 827, iSTAT, and Cobas c501 as described above. The setting was a tertiary referral center. Blood samples were collected from a combination of patients in the intensive care unit, operating theaters and emergency room.All methods demonstrated excellent precision, even in the profoundly hyponatremic measurement range (Na120 mmol/L using a plasma reference method). However, agreement between the methods varied with the degree of hyponatremia. In the profoundly hyponatremic range, Radiometer whole blood sodium values were nearly identical to plasma reference sodium, while iSTAT whole blood sodium showed a consistent positive bias relative to plasma sodium in this range.If whole blood direct sodium measurements are compared with plasma sodium in profoundly hyponatremic patients consideration should be given to the use of Radiometer blood gas analyzers over iSTAT since the latter shows a positive bias relative to a plasma comparative method.

Objectives Point of care (POC) whole blood lactate testing may facilitate rapid detection of sepsis. We evaluated three POC methods against both plasma lactate comparison methods and a flow-injection mass spectrometric (MS) method. Design and Methods Nova StatStrip, Abbott i-STAT CG4 + and Radiometer ABL90 POC lactate methods were evaluated against the mean of Cobas Integra 400 and Vitros 350 plasma lactate. POC methods were also compared to a flow-injection mass spectrometric assay measuring lactate in ZnSO4-precipitated whole blood extracts. Intra- and inter-assay precision was determined using quality control material. Method comparison included specimens from normal donors at rest, after exertion, and after spiking with lactic acid. Results Intra- and inter-assay coefficient of variation was 6 mmol/L, all POC methods showed proportional negative bias compared to plasma methods; but this bias was not observed when compared to the MS method. Despite proportional negative bias, all POC methods demonstrated acceptable concordance (94–100%) with plasma lactate within the reference interval ( 4 mmol/L, commonly used clinical cut-offs for detection of sepsis. Conclusions POC lactate methods demonstrate acceptable concordance with plasma lactate across commonly used clinical cut-offs for detection of sepsis. Due to systematic negative bias at higher lactate concentrations, POC and plasma lactate should not be used interchangeably to monitor patients with elevated lactate concentrations.

Objectives After several hemolyzed blood samples were received in the laboratory, we investigated lipid emulsion/TPN as a novel cause of hemolysis. Design and methods Whole blood was spiked with lipid emulsion and TPN. Results Hemolysis was proportional to the amount of lipid emulsion present in whole blood, with less hemolysis occurring in blood gas syringes compared to vacutainer tubes. Conclusion Collection of specimens in blood gas syringes may prevent hemolysis in patients on lipid emulsion.

The performance of three point of care methods for pleural fluid pH analysis was compared to a currently validated blood gas analyzer.An ABL 725 (Radiometer America, Westlake, OH) was used as the reference method to evaluate three cartridge-based assays: ABL 90 FLEX (Radiometer), and i-STAT 1 (Abbott Point of Care, Abbott Park, IL) CG4+ and G3+ cartridges for pleural fluid pH analysis. Pooled residual pleural fluid samples and quality control material were analyzed to determine intra- and inter-assay precision. Method comparison was performed with spiked (n=40) and clinically-ordered (n=10) pleural fluid samples across the analytical measuring range.All methods demonstrated inter-assay CVs0.1% at pH values of 7.1 and 7.6, and intra-assay CVs0.3% at pH values of 7.2 and 7.7. Bland-Altman plots demonstrated clinically significant bias between ABL 725 and each cartridge-based method only at pH7.6. For samples with pH7.6 mean bias vs. ABL 725 was -0.01 for ABL 90 FLEX and 0.03 for i-STAT 1 CG4+ and G3+ cartridges. Clinical concordance using a decision limit of pH7.2 was 96-98% for the three methods.Analytical and clinical performance of the three cartridge-based methods was comparable to a validated blood gas analyzer for pleural fluid pH analysis. Cartridge-based pH methods offer the advantage of easier troubleshooting for clots and clogs as they use disposable electrodes. However cartridge-based methods are not currently FDA-approved for pleural fluid samples, such that additional validation would be required for this specimen type.

Objectives To minimize toxicity of high-dose methotrexate (MTX) therapy, urinary alkalinization with frequent monitoring of urine pH is required. Urine pH is usually assessed by fast and convenient dipstick methods. When urine color interferes with dipstick measurement, as occurs in patients receiving MTX, alternative methods such as pH meters are used. Nursing staff caring for patients on high-dose MTX reported that urine pH results from dipstick and pH analyzers were often clinically discordant. As a result urine pH by dipstick and pH meter were compared in patients on high-dose MTX therapy and patients with normal-colored urine samples. Design and methods We measured urine pH by dipstick and pH meter in 116 urine samples from 4 patients receiving high-dose MTX therapy, and in 50 normal-colored urine samples from 50 patients not on MTX therapy. Results In patients on MTX therapy the mean (± standard deviation) bias between dipstick and pH meter urine pH was 0.7 ± 0.4, compared to 0.4 ± 0.3 in patients not on MTX. For patients on MTX clinical concordance between dipstick and pH meter urine results was poor around a clinical cut-off of pH 8.0. Of the 92 samples with a meter urine pH ≤ 8.0, 72 had a discordant value by dipstick (pH > 8). Conclusions Urine pH readings by dipstick and pH meter are not equivalent, and the bias between them is exacerbated in patients on MTX. Institutions with high-dose MTX therapy protocols should not alternate between dipstick and pH meter urine pH monitoring.