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Background Methylmalonic acid (MMA) can detect functional vitamin B12 deficiencies as it accumulates early when intracellular deficits arise. However, impaired clearance of MMA from blood due to decreased glomerular filtration rate (eGFR) also results in elevated plasma MMA concentrations. Alternative to clinical trials, a data mining approach was chosen to quantify and compensate for the effect of decreased eGFR on MMA concentration. Methods Comprehensive data on patient's vitamin B12, eGFR and MMA concentrations were collected ( n = 2906). The relationship between vitamin B12, renal function (eGFR) and MMA was modelled using weighted multiple linear regression. The obtained model was used to estimate the influence of decreased eGFR on MMA. Clinical impact was examined by comparing the number of patients labelled vitamin B12 deficient with and without adjustment in MMA. Results Adjusting measured MMA concentrations for eGFR in the group of patients with low-normal vitamin B12 concentrations (90-300 pmol/L) showed that the use of unadjusted MMA concentrations overestimates vitamin B12 deficiency by 40%. Conclusions Through a data mining approach, the influence of eGFR on the relation between MMA and vitamin B12 can be quantified and used to correct the measured MMA concentration for decreased eGFR. Especially in the elderly, eGFR-based correction of MMA may prevent over-diagnosis of vitamin B12 deficiency and corresponding treatment. [ABSTRACT FROM AUTHOR]

We observed 30% discrepancy between liquid chemistry and dry chemistry analysers for the determination of total bilirubin in human adult serum samples, which were consistent with a 20% overestimation and 10% underestimation relative to a Jendrassik-Grof reference method, respectively. In contrast, standard reference material SRM916, which was recently recommended as being the most suitable material for attaining interlaboratory agreement, shows very good agreement on both types of analysers, as well as close to 100% recovery with respect to the reference method. We show that the liquid vs. dry bilirubin discrepancies seem to originate in the presence of either conjugated or δ-bilirubin. Our observations make it clear that good interlaboratory (or inter-analyser) agreement between bilirubin reference materials does not guarantee the same for bilirubin concentrations in human serum samples. [ABSTRACT FROM AUTHOR]

Standardization of laboratory results allows for the use of common reference intervals and can be achieved via calibration of field methods with second- ary reference materials. These harmonization materials should be commutable, i.e., they produce identical numerical results independent of assay principle or platform. This study assessed the commutability of a cryolyoprotectant-containing harmonization material, obtained from the Dutch Foundation for Quality Assessment in Clinical Laboratories, that is intended to harmonize measurements of enzyme activities within the Dutch project "Calibration 2000". The catalytic concentrations of alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, γ-glutamyltransferase and creatine kinase were analyzed in pooled patient sera and in the reference material in 14 laboratories. On liquid chemistry analyzers the harmonization material behaves like patient material. The enzyme activities measured in it fall on the regression lines calculated from activities measured in serum samples. For dry chemistry analyzers the activities of alt enzymes measured in the harmonizator differ from the serum- based regression line. We show that this is due to the sucrose-containing cryolyoprotectant in the harmonization material. For each enzyme, correction factors were calculated that compensated for the bias and proved to be constant between reagent lots. Depending on the enzyme activity measured, application of these factors leads to 2- to 10-fold reduction of between-laboratory percentage coefficient of variation. Thus, additives to (potential) reference materials may alter their matrix in a way that interferes with analysis on certain test systems. The bias caused may be quantifiable and correctable. Establishment of correction factors leads to analytical uncertainties and costs. Therefore, matrix-based materials without additives should be selected as reference materials. [ABSTRACT FROM AUTHOR]

Objectives: Because some concern has been raised about the storage time of red blood cells and outcomes after cardiac surgery, we investigated whether longer storage time of transfused plasma increases the risk for early or late mortality among patients who have undergone coronary artery bypass grafting. Methods: We retrospectively analyzed the data of all 10,626 patients who underwent isolated coronary artery bypass grafting in Catharina Hospital, Eindhoven, The Netherlands, between January 1998 and December 2007. All patients who received at least 1 unit of plasma intraoperatively or during the first 5 postoperative days were studied. They were divided into 3 groups (only younger plasma, only older plasma, and any older plasma groups) according to the storage time of the plasma (cutoff point, 323 days). Results: After we had excluded 122 patients who were unavailable for follow-up, we found that 375 of the remaining patients (n = 745) received only younger plasma 370 patients received any older plasma, and 200 patients received only older plasma (mean follow-up, 1565 ± 1137 days; median follow-up, 1629 days). The storage time of plasma, when entered as either a continuous variable or a dichotomous variable, was a risk factor for early but not late mortality. Log-rank testing revealed no statistical difference in long-term survival among the groups. Conclusions: Longer storage time of plasma is a risk factor for early but not late mortality among patients who have undergone coronary artery bypass grafting. [Copyright &y& Elsevier]

Establishing dihydropyrimidine dehydrogenase (DPD) activity is highly important in determining the correct starting dose of fluoropyrimidines such as 5-fluorouracil and capecitabine. The concentration ratio of endogenous uracil with its metabolite dihydrouracil (DHU) is a well-known parameter that is linked to DPD activity. Concentration ratios such as thymine over its DPD-converted metabolite dihydrothymine (DHT) is less described and may serve as an alternative diagnostic biomarker for DPD activity. In this study, we describe the development and validation of an ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) assay for the quantification of uracil, DHU, thymine, and DHT in human plasma. In addition, stability experiments were performed. Uracil and thymine were quantified up to 80.0 ng/mL and DHU and DHT up to 800 ng/mL. Intra- and inter-assay precision were maximum 8.0 % and 7.6 %. respectively. Also, recovery was adequate and significant matrix-effects and carry-over were excluded. Stability experiments showed that uracil concentrations increased with 27–52 % when stored for 1 or 2 h at ambient temperatures compared to cold storage. Thymine, DHU, and DHT concentrations remained stable, thymine after 1 h in plasma excluded, showing the DHT:T ratio might be a more robust marker for DPD activity than DHU:U. In conclusion, we present here a novel assay capable of quantifying uracil, thymine, DHU and DHT in a single analytical run. We provide additional data showing increased stability for DHU, thymine and DHT compared to uracil. This assay may be used as a diagnostic test in future studies, establishing the association of these endogenous biomarker concentrations with DPD activity and safety to treatment with fluoropyrimidines. In addition, future research should also be focused on reducing pre-analytical instability. Standardization in this field is essential to set proper reference values and to allow inter-study comparison on clinical outcomes. • New LC-MS/MS method for simultaneous quantification of uracil, DHU, thymine and DHT. • Endogenous DPD substrates may be used as diagnostic marker for DPD deficiency. • Uracil increased with 27–52 % when stored for 1 or 2 h at ambient temperature. • Thymine, DHU and DHT remain stable when stored at ambient temperature. • Reviewed literature confirms high variation in pre-analytical storage stability. [ABSTRACT FROM AUTHOR]