scholarly journals Comparison of Serum and Plasma Methylmalonic Acid Measurements in 13 Laboratories: An International Study

1999 ◽  
Vol 45 (12) ◽  
pp. 2236-2242 ◽  
Author(s):  
Christine M Pfeiffer ◽  
S Jay Smith ◽  
Dayton T Miller ◽  
Elaine W Gunter
Keyword(s):  
Methylmalonic Acid ◽  
External Quality Assessment ◽  
International Study ◽  
Cobalamin Deficiency ◽  
Gas Chromatography Mass Spectrometry ◽  
Plasma Samples ◽  
Consensus Mean ◽  
Edta Plasma ◽  
Analytical Imprecision ◽  
The Mean

Abstract Background: Detection of cobalamin deficiency is increasingly important, and methylmalonic acid (MMA) appears to be a useful marker. Information on interlaboratory variation and on methodological differences for MMA in serum and plasma is limited. Methods: Using gas chromatography/mass spectrometry, 13 laboratories participated in a 2-day analysis of 8 serum and 11 EDTA-plasma specimens. Results were analyzed for imprecision, recovery, and differences among laboratories and methods. Results: The mean among-laboratory imprecision (CV) was 19% and 21% for serum and plasma samples, respectively, and 9.3% and 7.8% for serum and plasma samples with added MMA, respectively. The mean within-laboratory (among-run) CV was 13% for both serum and plasma samples and 5.2% and 4.9% for serum and plasma samples with added MMA. Within-method imprecision was the same or higher than among-method imprecision. The mean among-laboratory recovery of MMA was 105% and 95% in serum and plasma, respectively. Most laboratories showed a proportional bias relative to the consensus mean of up to 15%. Two laboratories reported results that on average were almost 30% higher than the consensus mean. Conclusions: No method differences were found, but significant among-laboratory imprecision was found in the present study. Improvements are needed to reduce the analytical imprecision of most laboratories, and attention must be focused on calibration issues. Differences among laboratories can be improved by introducing high-quality reference materials and by instituting external quality assessment programs.

scholarly journals Comparison of Plasma Total Homocysteine Measurements in 14 Laboratories: An International Study

1999 ◽  
Vol 45 (8) ◽  
pp. 1261-1268 ◽  
Author(s):  
Christine M Pfeiffer ◽  
Dan L Huff ◽  
S Jay Smith ◽  
Dayton T Miller ◽  
Elaine W Gunter
Keyword(s):  
International Study ◽  
Systematic Difference ◽  
Background Information ◽  
Gas Chromatography Mass Spectrometry ◽  
Plasma Samples ◽  
Derivatizing Agent ◽  
Analytical Imprecision ◽  
Total Homocysteine ◽  
The Mean ◽  
Plasma Total Homocysteine

Abstract Background: Information on interlaboratory variation and especially on methodological differences for plasma total homocysteine is lacking. Methods: We studied 14 laboratories that used eight different method types: HPLC with electrochemical detection (HPLC-ED); HPLC with fluorescence detection (HPLC-FD) further subdivided by type of reducing/derivatizing agent; gas chromatography/mass spectrometry (GC/MS); enzyme immunoassay (EIA); and fluorescence polarization immunoassay (FPIA). Three of these laboratories used two methods. The laboratories participated in a 2-day analysis of 46 plasma samples, 4 additional plasma samples with added homocystine, and 3 plasma quality-control (QC) pools. Results were analyzed for imprecision, recovery, and methodological differences. Results: The mean among-laboratory and among-run within-laboratory imprecision (CV) was 9.3% and 5.6% for plasma samples, 8.8% and 4.9% for samples with added homocystine, and 7.6% and 4.2% for the QC pools, respectively. Difference plots showed values systematically higher than GC/MS for HPLC-ED, HPLC-FD using sodium borohydride/monobromobimane (however, for only one laboratory), and EIA, and lower values for HPLC-FD using trialkylphosphine/4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole. The two HPLC-FD methods using tris(2-carboxyethyl) phosphine/ammonium 7-fluoro-2,1,3-benzoxadiazole-4-sulfonate (SBD-F) or tributyl phosphine/SBD-F, and the FPIA method showed no detectable systematic difference from GC/MS. Conclusions: Among-laboratory variations within one method can exceed among-method variations. Some of the methods tested could be used interchangeably, but there is an urgent need to improve analytical imprecision and to decrease differences among methods.

scholarly journals External Quality Assessment of Methylmalonic Acid and Total Homocysteine

1999 ◽  
Vol 45 (9) ◽  
pp. 1536-1542 ◽  
Author(s):  
Jan Møller ◽  
Karsten Rasmussen ◽  
Lene Christensen
Keyword(s):  
Gas Chromatography ◽  
Quality Assessment ◽  
Methylmalonic Acid ◽  
External Quality Assessment ◽  
Mass Spectrometric ◽  
External Quality ◽  
Laboratory Component ◽  
Edta Plasma ◽  
Total Homocysteine ◽  
Minimum Quality

Abstract Background: The use of analyses for methylmalonic acid (MMA) and total homocysteine (HCY) in plasma has become widespread. Realizing the need for external quality assessment for these measurements, we started a program in 1997. The results for 1998 are reviewed in this report. Methods: Fourteen laboratories participated with 15 sets of results for MMA, and 28 laboratories participated with 34 sets of results for HCY. Results for four identical samples, made up from the same unmodified serum (MMA) or EDTA-plasma (HCY) pool, sent out under different identifications, were used for assessing the imprecision. Samples made up from the same pools supplemented with MMA or l-HCY to three concentrations were used for assessing the recovery. By using literature data for the biological variation, quality goals for both analytes were calculated. Results: The overall within-laboratory CV was 12% for MMA and 7.5% for HCY. Gas chromatography–mass spectrometric HCY results had lower imprecision than the HPLC or immunoassay results. For MMA, no significant between-laboratory component of variance was found. Only results for HCY obtained with HPLC methods showed significant between-laboratory variance. Conclusions: Eight of the 15 participants achieved the minimum imprecision goal for MMA vs 9 of the 34 participants for HCY. The minimum quality goals for bias as approximated by the recovery were achieved by 13 participants for MMA and 26 for HCY.

scholarly journals Accuracy of determination of the glomerular filtration marker iohexol by European laboratories as monitored by external quality assessment

2019 ◽  
Vol 57 (7) ◽  
pp. 1006-1011 ◽  
Author(s):  
Gunnar Nordin ◽  
Sara Ekvall ◽  
Carolina Kristoffersson ◽  
Ann-Sofie Jonsson ◽  
Sten-Erik Bäck ◽  
...  
Keyword(s):  
Glomerular Filtration Rate ◽  
Quality Assessment ◽  
Glomerular Filtration ◽  
Filtration Rate ◽  
External Quality Assessment ◽  
Plasma Samples ◽  
High Quality ◽  
External Quality ◽  
The Mean

Abstract Background Glomerular filtration is the most important kidney function. The most accurate glomerular filtration rate (GFR) estimates are based on the clearance of exogenous filtration markers. Of these, iohexol is the only exogenous marker that is included in an external quality assessment (EQA) scheme. The aim of the present study was to evaluate the performance of the European laboratories participating in Equalis’ EQA scheme for iohexol. Methods Weighed amounts of iohexol (Omnipaque) were added to plasma samples and distributed to laboratories participating in the EQA scheme for iohexol. All laboratories performed the assays in a blinded fashion. Results The number of participating laboratories varied between 27 and 34 during the study period. Iohexol was determined by HPLC in 77% of the laboratories and by UPLC/MS/MS methods in 15% of the laboratories. The mean interlaboratory coefficient of variation was 4.7% for the HPLC methods and 6.4% for the UPLC/MS/MS methods. The mean bias between calculated and measured iohexol values was –1.3 mg/L (95% confidence interval ±0.3) during the first part of the study period and 0.1 mg/L (±0.3) during the later part. Conclusions The low interlaboratory variation demonstrates that iohexol can be measured reliably by many laboratories and supports the use of iohexol as a GFR marker when there is a need for high quality GFR measurements.

scholarly journals Possible Mechanism for in Vitro Complement Activation in Blood and Plasma Samples: Futhan/EDTA Controls in Vitro Complement Activation

1999 ◽  
Vol 45 (8) ◽  
pp. 1190-1199 ◽  
Author(s):  
Philippe H Pfeifer ◽  
Marleen S Kawahara ◽  
Tony E Hugli
Keyword(s):  
Liver Transplant ◽  
Complement Activation ◽  
Room Temperature ◽  
Plasma Samples ◽  
Accurate Analysis ◽  
Transplant Patients ◽  
Edta Plasma ◽  
The Mean

Abstract Background: Ongoing in vitro complement (C) activation in citrate or EDTA plasma has prevented an accurate analysis of C-activation products generated in vivo. The aim of this study was to characterize handling and storage conditions required to prevent in vitro C activation in blood and plasma samples collected with Futhan/EDTA. Methods: BiotrakTM RIAs were used to quantitatively measure C3a and C4a in blood and/or plasma samples from healthy individuals (controls) and from liver transplant patients. Blood samples were routinely drawn into either EDTA (1 g/L) tubes or into tubes containing both EDTA (1 g/L) and Futhan (0.1 g/L) and immediately centrifuged at 2000g for 15 min at 4 °C. Results: In controls, C4a, but not C3a, in fresh samples (time 0) was higher in EDTA plasma than in Futhan/EDTA plasma (n = 20; P = 0.002). Futhan/EDTA prevented C3a and C4a generation in blood and plasma samples held at room temperature (22–23 °C) for 1 h and in plasma held for 24 h at 4 °C or −70 °C. The mean C3a concentration (1.76 mg/L; n = 19) at time 0 in EDTA plasma samples from liver transplant patients was significantly higher than for controls (0.34 mg/L; n = 11). In these patients, the mean C3a in EDTA samples increased to 13.8 mg/L after 60 min at room temperature, but there was no change in the C3a concentration of an EDTA plasma from a control. In the patients, C3a concentrations were lower in Futhan/EDTA plasma than in EDTA at time 0 and after 60 min at room temperature (1.40 and 2.02 mg/L, respectively). The mean patient C4a was 4.02 mg/L in EDTA plasma at time 0 vs 0.24 mg/L for controls; it increased to 16.9 mg/L after 60 min at room temperature compared with 0.76 mg/L for controls. The mean patient C4a was 0.83 mg/L in Futhan/EDTA plasma at time 0 vs 0.1 mg/L for controls. Neither patient nor control C4a concentrations increased vs time in Futhan/EDTA. Conclusion: The combination of Futhan (0.1 g/L) and EDTA (1 g/L) eliminates in vitro C activation.

Validity of the Consensus Mean as the Target Value for a Small External Quality Assessment Scheme

1985 ◽  
Vol 22 (3) ◽  
pp. 283-290 ◽  
Author(s):  
R J Georges
Keyword(s):  
Quality Assessment ◽  
Coefficient Of Variation ◽  
Analytical Methods ◽  
Close Agreement ◽  
External Quality Assessment ◽  
External Quality ◽  
External Quality Assessment Scheme ◽  
Mean Values ◽  
Consensus Mean ◽  
The Mean

Data from 2 years' operation of an External Quality Assessment Scheme covering 14 analytes and with some 60 participants is presented. Following the trimming of discrepant results and statistical ‘outliers' (outside the range of ±3 SD from the mean), there was generally close agreement between consensus mean values for a specimen analysed on different occasions, by different groups of laboratories, or when using different analytical methods. An improvement in performance, indicated by a reduction in the average inter-laboratory coefficient of variation was found for 11 of the 14 analytes over the 2-year period.

Methylmalonic Acid Concentration in Serum Not Affected in Hepatic Disease

1992 ◽  
Vol 38 (4) ◽  
pp. 493-495 ◽  
Author(s):  
L Hagelskjaer ◽  
K Rasmussen
Keyword(s):  
Methylmalonic Acid ◽  
Hepatic Disease ◽  
Cobalamin Deficiency ◽  
Metabolic Abnormalities ◽  
Test Results ◽  
High Concentration ◽  
False Positive Test ◽  
Hepatic Diseases ◽  
The Mean ◽  
Mean Concentration

Abstract Accumulation of methylmalonic acid may provide an early clue to deficiency of cobalamin (vitamin B12) in tissue. Metabolic abnormalities involving precursors of methylmalonic acid are frequently observed in patients with hepatic diseases. To establish whether methylmalonic acid accumulates and thereby gives false-positive test results for cobalamin deficiency, we measured the concentration of methylmalonic acid in serum of patients with various hepatic diseases. Many of the patients had increased concentrations of cobalamin in serum. In serum from 70 patients, the mean concentration of methylmalonic acid (252, SE 25 nmol/L) did not differ significantly from that found in healthy subjects (211, SE 12 nmol/L). We conclude that the assay of methylmalonic acid in serum may be useful for evaluating cobalamin status in hepatic disease with functional cobalamin deficiency despite an artificially increased normal or high concentration of cobalamin in serum.

Pregnancy in Patients With AQP4-Ab, MOG-Ab, or Double-Negative Neuromyelitis Optica Disorder

Neurology ◽  
2021 ◽  
Vol 96 (15) ◽  
pp. e2006-e2015
Author(s):  
Nicolas Collongues ◽  
Cecilia Alves Do Rego ◽  
Bertrand Bourre ◽  
Damien Biotti ◽  
Romain Marignier ◽  
...  
Keyword(s):  
Neuromyelitis Optica ◽  
Previous History ◽  
International Study ◽  
Myelin Oligodendrocyte Glycoprotein ◽  
Double Negative ◽  
Neuromyelitis Optica Spectrum Disorder ◽  
Pregnancy And Postpartum ◽  
History Of ◽  
Mog Antibodies ◽  
The Mean

ObjectiveTo analyze the effects of pregnancy on neuromyelitis optica spectrum disorder (NMOSD) according to patients' serostatus and immunosuppressive therapy (IST).MethodsWe performed a retrospective multicenter international study on patients with NMOSD. Patients were tested for aquaporin-4 (AQP4) and myelin oligodendrocyte glycoprotein (MOG) antibodies (Ab). Informative pregnancies were reported when NMOSD onset occurred before or during pregnancy or up to 12 months postpartum. The mean annualized relapse rate (ARR) was calculated for the 12 months before conception, for each trimester of pregnancy, and postpartum. Events such as miscarriage, abortion, and preeclampsia were reported. IST was considered if taken in the 3 months before or during pregnancy.ResultsWe included 89 pregnancies (46 with AQP4-Ab, 30 with MOG-Ab, and 13 without either Ab) in 58 patients with NMOSD. Compared to the prepregnancy period, the ARR was lower during pregnancy in each serostatus group and higher during the postpartum period in patients with AQP4-Ab (p < 0.01). Forty-eight percent (n = 31) of pregnancies occurred during IST and these patients presented fewer relapses during pregnancy and the 12 months postpartum than untreated patients (26% vs 53%, p = 0.04). Miscarriages occurred in 10 (11%) pregnancies, and were mainly in patients with AQP4-Ab (with or without IST) and a previous history of miscarriage. Preeclampsia was reported in 2 (2%) patients who were AQP4-Ab-positive.ConclusionWe found a rebound in the ARR during the first postpartum trimester that was higher than the prepregnancy period only in AQP4-Ab-positive patients. Taking IST just before or during pregnancy reduces the risk of relapses in these conditions.

scholarly journals Detection of Neprilysin-Derived BNP Fragments in the Circulation: Possible Insights for Targeted Neprilysin Inhibition Therapy for Heart Failure

2019 ◽  
Vol 65 (10) ◽  
pp. 1239-1247 ◽  
Author(s):  
Evgeniya E Feygina ◽  
Marina M Artemieva ◽  
Alexander B Postnikov ◽  
Natalia N Tamm ◽  
Marina N Bloshchitsyna ◽  
...  
Keyword(s):  
Heart Failure ◽  
Ring Opening ◽  
Active Form ◽  
Cross Reactivity ◽  
Plasma Samples ◽  
Time Points ◽  
Positive Effects ◽  
Edta Plasma ◽  
Neprilysin Inhibition ◽  
Nep Inhibition

Abstract BACKGROUND Entresto™ is a new heart failure (HF) therapy that includes the neprilysin (NEP) inhibitor sacubitril. One of the NEP substrates is B-type natriuretic peptide (BNP); its augmentation by NEP inhibition is considered as a possible mechanism for the positive effects of Entresto. We hypothesized that the circulating products of BNP proteolysis by NEP might reflect NEP impact on the metabolism of active BNP. We suggest that NEP-based BNP cleavage at position 17–18 results in BNP ring opening and formation of a novel epitope with C-terminal Arg-17 (BNP-neo17 form). In this study, we use a specific immunoassay to explore BNP-neo17 in a rat model and HF patient plasma. METHODS We injected BNP into rats, with or without NEP inhibition with sacubitril. BNP-neo17 in plasma samples at different time points was measured with a specific immunoassay with neglectable cross-reactivity to intact forms. BNP-neo17 and total BNP were measured in EDTA plasma samples of HF patients. RESULTS BNP-neo17 generation in rat circulation was prevented by NEP inhibition. The maximum 13.2-fold difference in BNP-neo17 concentrations with and without sacubitril was observed at 2 min after injection. BNP-neo17 concentrations in 32 HF patient EDTA plasma samples ranged from 0 to 37 pg/mL (median, 5.4; interquartile range, 0–9.1). BNP-neo17/total BNP had no correlation with total BNP concentration (with r = −0.175, P = 0.680) and showed variability among individuals. CONCLUSIONS BNP-neo17 formation is NEP dependent. Considering that BNP-neo17 is generated from the active form of BNP by NEP, we speculate that BNP-neo17 may reflect both the NEP activity and natriuretic potential and serve for HF therapy guidance.

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