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An imbalance in circulating factors that regulate blood vessel formation and health, referred to as angiogenic factors, plays a central role in the pathogenesis of preeclampsia.

Several studies have demonstrated a strong association between altered circulating angiogenic factors and preeclampsia. These factors include circulating antiangiogenic proteins such as soluble fms-like tyrosine kinase 1 and soluble endoglin and proangiogenic protein such as placental growth factor. Abnormalities in these circulating angiogenic factors are not only present during clinical disease, but also antedate clinical signs and symptoms by several weeks. These alterations are particularly prominent in patients who present with preeclamptic signs and symptoms prematurely and/or in patients with severe preeclampsia. The availability of automated platforms for the rapid measurement of circulating angiogenic proteins in blood samples has now allowed researchers and clinicians to evaluate the utility of these assays in the diagnosis of the disease, in the stratification of patients in clinical trials, or in the monitoring of therapies. In this review we highlight the various studies that have been performed, with a focus on large validation studies.

Measurement of circulating angiogenic proteins for the diagnosis and prediction of preeclampsia is still at an early stage but is rapidly evolving. Standardization across the various automated platforms and prospective studies that demonstrate clinical utility are needed.

Vitamin D testing is increasing worldwide. Recently several diagnostic manufacturers including Abbott and Siemens have launched automated 25-hydroxy vitamin D (25OH-D) immunoassays. Furthermore, preexisting assays from DiaSorin and Roche have recently been modified. We compared the performance of 5 automated immunoassays, an RIA and 2 liquid chromatography–tandem mass spectrometry (LC-MS/MS) methods.

Aliquots of 170 randomly selected patient samples were prepared and 25OH-D was measured by 2 LC-MS/MS methods, an RIA (DiaSorin), and automated immunoassays from Abbott (Architect), DiaSorin (LIAISON), IDS (ISYS), Roche (E170, monoclonal 25OH-D₃ assay), and Siemens (Centaur). Within-run and between-run imprecision were evaluated by measurement of 5 replicates of 2 serum pools on 5 consecutive days.

The LC-MS/MS methods agreed, with a concordance correlation coefficient (CCC) of 0.99 and bias of 0.56 μg/L (1.4 nmol/L). The RIA assay showed a performance comparable to LC-MS/MS, with a CCC of 0.97 and a mean bias of 1.1 μg/L (2.7 nmo/L). All immunoassays measured total 25OH-D (including D₃ and D₂), with the exception of the Roche assay (D₃ only). Among the immunoassays detecting total 25OH-D, the CCCs varied between 0.85 (Abbott) to 0.95 (LIAISON). The mean bias ranged between 0.2 μg/L (0.5 nmol/L) (LIAISON) and 4.56 μg/L (11.4 nmol/L) (Abbott). The Roche 25OH-D₃ assay demonstrated small mean bias [–2.7 μg/L (–6.7 nmol/L)] [–2.7 μg/L (–6.7 nmol/L)] but a low CCC of just 0.66. Most assays demonstrated good intra- and interassay precision, with CV <10%.

Automated immunoassays demonstrated variable performance and not all tests met our minimum performance goals. It is important that laboratories be aware of the limitations of their assay.

Recent recognition of its broad pathophysiological importance has triggered an increased interest in 25-hydroxyvitamin D [25(OH)D]. By consequence, throughput in 25(OH)D testing has become an issue for clinical laboratories, and several automated assays for measurement of 25(OH)D are now available. The aim of this study was to test the accuracy and robustness of these assays by comparing their results to those of an isotope dilution/online solid-phase extraction liquid chromatography/tandem mass spectrometry (ID-XLC-MS/MS) method. We put specific focus on the influence of vitamin D–binding protein (DBP) by using samples with various concentrations of DBP.

We used 5 automated assays (Architect, Centaur, iSYS, Liaison, and Elecsys), 1 RIA (Diasorin) preceded by extraction, and an ID-XLC-MS/MS method to measure 25(OH)D concentrations in plasma samples of 51 healthy individuals, 52 pregnant women, 50 hemodialysis patients, and 50 intensive care patients. Using ELISA, we also measured DBP concentrations in these samples.

Most of the examined 25(OH)D assays showed significant deviations in 25(OH)D concentrations from those of the ID-XLC-MS/MS method. As expected, DBP concentrations were higher in samples of pregnant women and lower in samples of IC patients compared to healthy controls. In 4 of the 5 fully automated 25(OH)D assays, we observed an inverse relationship between DBP concentrations and deviations from the ID-XLC-MS/MS results.

25(OH)D measurements performed with most immunoassays suffer from inaccuracies that are DBP concentration dependent. Therefore, when interpreting results of 25(OH)D measurements, careful consideration of the measurement method is necessary.

Extracellular matrix alterations are important elements in the arterial changes seen in diabetes, being associated with increased vascular stiffness and the development of cardiovascular diseases. However, no biomarkers for diabetes-related arterial changes have been defined.

Mammary artery specimens from 17 men with type 2 diabetes and 18 nondiabetic individuals were used for microarray expression profiling, quantitative real-time PCR, immunoassay, and immunohistochemical analyses. A derived candidate marker, fibulin-1, which is an elastin-associated matrix molecule, was measured immunochemically in plasma from (a) 70 patients scheduled for vascular surgery, (b) 305 patients with type 2 diabetes examined with carotid ultrasonography and echocardiography, and (c) 308 patients with type 2 diabetes, followed for 15 years.

The most upregulated transcript in nonatherosclerotic arterial tissue from patients with type 2 diabetes encoded the extracellular matrix protein, fibulin-1. Higher concentrations of fibulin-1-protein were present in artery extracts from patients with diabetes than extracts from individuals without diabetes, and increased fibulin-1 immunostaining was apparent around the external elastic lamina of diabetic arteries. Patients with diabetes displayed increased plasma concentrations of fibulin-1 (P = 0.006). Plasma fibulin-1 concentrations correlated with hemoglobin A_1c (P < 0.001), arterial stiffness indices including pulse pressure (P < 0.001), and carotid compliance (P = 0.004), as well as plasma N-terminal pro–B-type natriuretic peptide concentrations (P < 0.001) and were predictive of 15-year mortality (P = 0.013).

Fibulin-1 accumulates in the arterial wall and in plasma of patients with type 2 diabetes, and appears to be a factor associated with arterial extracellular matrix changes in type 2 diabetes.

Determination of the aldosterone-to-renin ratio (ARR) in blood is the preferred screening test for primary aldosteronism. Renin can be measured as the plasma renin activity (PRA) or the plasma renin concentration (PRC). Consequently, the ARR can be measured either based on the PRA (ARR_pra) or based on the PRC (ARR_prc). In contrast with the ARR_pra, the data on reference values for the ARR_prc are limited. Moreover, whether the ARR_pra or ARR_prc is affected by variations in salt intake is unknown.

We measured the PRA, the PRC, and serum aldosterone in 100 normotensive individuals between 20 and 70 years of age before and after a 3-day oral sodium-loading test (SLT). Participants were stratified according to age and sex. Data are presented as the median and interquartile range (IQR).

Urinary sodium excretion after the SLT was ≥200 mmol/24 h in all participants. Serum aldosterone, PRA, and PRC values were significantly reduced after the SLT. PRC and PRA results were highly correlated [Spearman rank correlation r_s = 0.80 and 0.74 before and after SLT, respectively; P < 0.001 for both]. The central 95% reference intervals for ARR_pra before and after SLT were 0.07–1.45 h^–1 and 0.06–1.84 h^–1, respectively. The corresponding reference intervals for ARR_prc were 4.1–81.3 pmol/ng and 3.9–74.8 pmol/ng. The median ARR_prc decreased after the SLT from 19.5 pmol/ng (IQR, 13.0–29.4 pmol/ng) to 18.6 pmol/ng (IQR, 9.4–27.1 pmol/ng) (P = 0.005), whereas the median ARR_pra did not change (P = 0.12). Both the ARR_prc and ARR_pra at baseline were higher in women than in men, whereas no sex difference was observed after sodium loading.

We present reference values for the ARR_prc for healthy individuals. The ARR is affected to a variable degree by sex and sodium intake.

Recent reports of new and important roles for serotonin (5-hydroxytryptamine, 5-HT) in the periphery have substantially increased interest in measuring peripheral serotonin. Nearly all circulating serotonin is found within platelets and this pool has been assessed by measuring serotonin in whole blood or in platelet-rich plasma. Measurement of the much smaller but potentially critically important pool of human free plasma serotonin in platelet-poor plasma (PPP) has proven much more difficult, with a wide range of reference values reported.

To characterize the available data we carried out a systematic literature search of previous reports of PPP serotonin and attempted to determine the best estimate of true PPP serotonin concentration in humans. A total of 101 published reports that included PPP serotonin values in healthy controls were found and included in the summary statistical analyses. The distribution of PPP serotonin values demonstrated high skewness (+1.98), and the reported values ranged from 0.6 to 179 nmol/L, with a mean of 31.6 nmol/L, an SD of 38.9 nmol/L, and a median of 14.8 nmol/L.

Reported concentrations for human PPP or free plasma serotonin were highly discrepant, with most reports giving erroneously high values that should be disregarded. Inherent difficulties in selectively measuring the extremely low concentrations of serotonin present in PPP and in preparing PPP without contamination from platelet-derived serotonin contributed to the problem, as did the failure of researchers to compare their results with those from prior studies. There is a clear and pressing need for reference materials for the measurement of plasma (PPP) serotonin.

A reference model for converting serum growth factor and bone metabolism markers into an SD score (SDS) is required for clinical practice. We aimed to establish reference values of serum insulin-like growth factor-1 (IGF-1) and IGF binding protein 3 (IGFBP-3) concentrations and bone metabolism markers in French children, to generate a model for converting values into SDS for age, sex, and pubertal stage.

We carried out a cross-sectional study of 1119 healthy white children ages 6–20 years. We assessed concentrations of serum IGF-1, IGFBP-3, carboxyterminal telopeptide α1 chain of type I collagen (CrossLaps), and bone alkaline phosphatase concentrations and height, weight, and pubertal stage, and used semiparametric regression to develop a model.

A single regression model to calculate the SDSs with an online calculator was provided. A positive relationship was found between SDS for serum IGF-1 and IGFBP-3, IGF/IGFBP-3 mol/L ratio, and anthropometric parameters (P < 0.0001), with slightly greater effects observed for height than for body mass index (BMI). There was a negative relationship between serum CrossLaps concentration and BMI, and a positive relationship between serum CrossLaps concentration and height. A comparison of serum IGF-1 reference databases for children showed marked variation as a function of age and pubertal group; smooth changes with age and puberty were observed only in our model.

This new model for the assessment of SDS reference values specific for age, sex, and pubertal stage may help to increase the diagnostic power of these parameters for the assessment of growth and bone metabolism disorders. This study also provides information about the physiological role of height and BMI for the interpretation of these parameters.