Interpretation of Folate Results in Hemolytic Plasma Samples:A Practical Approach

Folate analysis in plasma is affected by hemolysis, which can lead to biased results. However, the degree of hemolysis that is considered acceptable is unclear. We explored the relationship between folate concentration and degree of hemolysis. Heparin plasma samples (N=77, hemolysis index ≤10 μmol/L) were spiked with increasing amounts of corresponding patient-specific hemolysate. Subsequently, the folate concentration and hemolysis index were measured using two Roche Cobas platforms, and their incremental relationship was investigated. The folate concentration ranged from 2.9 to 30.9 nmol/L with a median (interquartile range) of 11.4 (8.6-19.1) nmol/L. The linear relationship between the increments in folate concentration and hemolysis index was approximated by the function y=1.86x+1.56 (R(2)=0.996), where x represents the laboratory-specific critical difference in folate concentration, which can be calculated from the analytical variation of the employed folate assay(s), and y represents the hemolysis threshold. The hemolysis threshold did not significantly differ between the tertiles of plasma folate concentration (P=0.10). In conclusion, we have provided an evidence-based approach that can be used to reliably interpret folate concentrations in hemolytic samples, independent of the patient’s folate status

Kidney Function in Patients With Neuromuscular Disease:Creatinine Versus Cystatin C

Background: Accurate measurement of kidney function in patients with neuromuscular disorders is challenging. Cystatin C, a marker not influenced by skeletal muscle degradation, might be of clinical value in these patients.Methods: We consecutively enrolled 39 patients with neuromuscular disorders. We investigated the association of the eGFR, based on plasma creatinine and Cystatin C, with clinical and biochemical variables associated with kidney function, namely age and galectin-3.Results: Creatinine-based eGFR was 242 (±80) and Cystatin C-based eGFR was 110 (±23) mL/min/1.73 m2. Cystatin C-based eGFR was associated with age (β −0.63 p < 0.0001) and galectin-3 levels (β −0.43 p < 0.01), while creatinine-based eGFR was not (β −0.22 p = 0.20; β −0.28 p = 0.10). Sensitivity analyses in Duchenne and Becker patients revealed the same results: Cystatin C-based eGFR was associated with age (β −0.61 p < 0.01) and galectin-3 levels (β −0.43 p = 0.05), while creatinine-based eGFR was not (β −0.32 p = 0.13; β −0.34 p = 0.14).Conclusions: These data indicate that estimation of renal function in patients with neuromuscular disorders cannot reliably be achieved with creatinine, while Cystatin C appears a reasonable alternative. Since a large proportion of patients with neuromuscular disorders develops heart failure, and requires heart failure medication, adequate monitoring of renal function is warranted

Folate reference interval estimation in the Dutch general population

Background: Folate functions as an enzyme co-factor within the one-carbon metabolic pathway, providing key metabolites required for DNA synthesis and methylation. Hence, insufficient intake of folate can negatively affect health. As correct interpretation of folate status is dependent on a well-established reference interval, we set out to perform a new estimation following the restandardization of the Roche folate assay against the international folate standard. Materials and methods: The folate reference interval was estimated using samples obtained from the Dutch population-based Lifelines cohort. The reference interval was estimated using two methods: a nonparametric estimation combined with bootstrap resampling and by fitting the data to a gamma distribution. The lower reference limit was verified in a patient cohort by combined measurement of folate and homocysteine. Results: Dependent on the method used for estimation and in- or exclusion of individuals younger than 21 years of age, the lower reference limit ranged from 6.8 to 7.3 nmol/L and the upper reference limit ranged from 26 to 38.5 nmol/L. Applying a lower reference limit of 7.3 nmol/L resulted in the following percentage of folate deficiencies over a period of 12 months: general practitioner 15.5% (IQR 4.0%), general hospital 12.8% (IQR 5.3%), academic hospital 9.6% (IQR 4.3%). Conclusions: We estimated the folate reference interval in the Dutch general population which is not affected by a folic acid fortification program and verified the obtained lower reference limit by homocysteine measurements. Based on our results, we propose a folate reference interval independent of age of 7.3-38.5 nmol/

High-density lipoprotein particles and their relationship to posttransplantation diabetes mellitus in renal transplant recipients

High concentrations of high-density lipoprotein (HDL) cholesterol are likely associated with a lower risk of posttransplantation diabetes mellitus (PTDM). However, HDL particles vary in size and density with yet unestablished associations with PTDM risk. The aim of our study was to determine the association between different HDL particles and development of PTDM in renal transplant recipients (RTRs). We included 351 stable outpatient adult RTRs without diabetes at baseline evaluation. HDL particle characteristics and size were measured by nuclear magnetic resonance (NMR) spectroscopy. During 5.2 (IQR, 4.1‒5.8) years of follow-up, 39 (11%) RTRs developed PTDM. In multivariable Cox regression analysis, levels of HDL cholesterol (hazard ratio [HR] 0.61, 95% confidence interval [CI] 0.40–0.94 per 1SD increase; p = 0.024) and of large HDL particles (HR 0.68, 95% CI 0.50–0.93 per log 1SD increase; p = 0.017), as well as larger HDL size (HR 0.58, 95% CI 0.36–0.93 per 1SD increase; p = 0.025) were inversely associated with PTDM development, independently of relevant covariates including, age, sex, body mass index, medication use, transplantation-specific parameters, blood pressure, triglycerides, and glucose. In conclusion, higher concentrations of HDL cholesterol and of large HDL particles and greater HDL size were associated with a lower risk of PTDM development in RTRs, independently of established risk factors for PTDM development

Plasma C-Peptide and Risk of Developing Type 2 Diabetes in the General Population

C-peptide measurement may represent a better index of pancreatic β-cell function compared to insulin. While insulin is mainly cleared by liver, C-peptide is mainly metabolized by kidneys. The aim of our study was to evaluate the association between baseline plasma C-peptide level and the development of type 2 diabetes independent of glucose and insulin levels and to examine potential effect-modification by variables related to kidney function. We included 5176 subjects of the Prevention of Renal and Vascular End-Stage Disease study without type 2 diabetes at baseline. C-peptide was measured in plasma with an electrochemiluminescent immunoassay. Cox proportional hazards regression was used to evaluate the association between C-peptide level and type 2 diabetes development. Median C-peptide was 722 (566-935) pmol/L. During a median follow-up of 7.2 (6.0-7.7) years, 289 individuals developed type 2 diabetes. In multivariable-adjusted Cox regression models, we observed a significant positive association of C-peptide with the risk of type 2 diabetes independent of glucose and insulin levels (hazard ratio (HR): 2.35; 95% confidence interval (CI): 1.49-3.70). Moreover, we found significant effect modification by hypertension and albuminuria (p < 0.001 and p = 0.001 for interaction, respectively), with a stronger association in normotensive and normo-albuminuric subjects and absence of an association in subjects with hypertension or albuminuria. In this population-based cohort, elevated C-peptide levels are associated with an increased risk of type 2 diabetes independent of glucose, insulin levels, and clinical risk factors. Elevated C-peptide level was not independently associated with an increased risk of type 2 diabetes in individuals with hypertension or albuminuria

Methylmalonic acid, vitamin B12, renal function, and risk of all-cause mortality in the general population:results from the prospective Lifelines-MINUTHE study

Background: Methylmalonic acid (MMA) is best known for its use as a functional marker of vitamin B12 deficiency. However, MMA concentrations not only depend on adequate vitamin B12 status, but also relate to renal function and endogenous production of propionic acid. Hence, we aimed to investigate to what extent variation in MMA levels is explained by vitamin B12 and eGFR and whether MMA levels are associated with mortality if vitamin B12 and eGFR are taken into account. Methods: A total of 1533 individuals (aged 60–75 years, 50% male) were included from the Lifelines Cohort and Biobank Study. Individuals were included between 2006 and 2013, and the total follow-up time was 8.5 years. Results: Median [IQR] age of the study population was 65 [62–69] years, 50% was male. At baseline, median MMA concentration was 170 [138–216] nmol/L, vitamin B12 290 [224–362] pmol/L, and eGFR 84 [74–91] mL/min/1.73 m2. Log 2 vitamin B12, log 2 eGFR, age, and sex were significantly associated with log 2 MMA in multivariable linear regression analyses (model R 2 = 0.22). After a total follow-up time of 8.5 years, 72 individuals had died. Log 2 MMA levels were significantly associated with mortality (hazard ratio [HR] 1.67 [95% CI 1.25–2.22], P < 0.001). Moreover, we found a significant interaction between MMA and eGFR with respect to mortality (P interaction < 0.001). Conclusions: Only 22% of variation in MMA levels was explained by vitamin B12, eGFR, age, and sex, indicating that a large part of variation in MMA levels is attributable to other factors (e.g., catabolism, dietary components, or gut microbial production). Higher MMA levels are associated with an increased risk for mortality, independent of vitamin B12, eGFR, and sex. This association was more pronounced in individuals with impaired renal function

Age dependency of plasma vitamin B12 status markers in Dutch children and adolescents

BACKGROUND: Vitamin B12 deficiency in children may be associated with (severe) neurological manifestations, therefore recognition is important. Diagnosing vitamin B12 deficiency in children is challenging. This study aimed to investigate plasma methylmalonic acid, holotranscobalamin, and total cobalamin in children 0–18 years of age and to estimate age-dependent reference intervals. METHODS: Plasma vitamin B12 markers were measured in collected plasma samples of 170 children 0–18 years visiting a local primary care laboratory. All had within-reference hemoglobin and MCV values. Pediatric plasma vitamin B12 biomarkers were measured and reference values were derived thereof. RESULTS: Plasma methylmalonic acid was higher in young children, in particular between 1 and 6 months of age; total cobalamin and holotranscobalamin were highest from 0.5 to 4 years and decreased till 10 years of age. Plasma holotranscobalamin was highly correlated with plasma total cobalamin; their ratio was independent of age. Plasma methylmalonic acid was slightly more related to total cobalamin than to holotranscobalamin. A large proportion of mainly young children would be misclassified when adult references are applied. CONCLUSIONS: Pediatric reference values for cobalamin markers are necessary to allow for early recognition and monitoring of children suspect of (clinical) cobalamin deficiency. IMPACT: We analyzed three plasma vitamin B12 status markers, i.e., total cobalamin, holotranscobalamin, and methylmalonic acid, in the plasma of 170 children 0–18 years of age and were able to derive reference intervals thereof. Recognition of vitamin B12 deficiency in children is important but challenging as pediatric reference intervals for plasma vitamin B12 status markers, particularly plasma holotranscobalamin, are not well described. We think that our results may help early recognition and monitoring of children suspect of (clinical) vitamin B12 deficiency