. Protein intake during hemodialysis maintains a positive whole body protein balance in chronic hemodialysis patients. Am J Physiol Endocrinol Metab 284: E954-E965, 2003. First published January 21, 2003 10.1152/ajpendo.00264.2002.-Protein energy malnutrition is present in 18 to 56% of hemodialysis patients. Because hemodialysis has been regarded as a catabolic event, we studied whether consumption of a protein-and energyenriched meal improves the whole body protein balance during dialysis in chronic hemodialysis (CHD) patients. Patients were studied on a single day between dialysis (HDϪ protocol) in the morning while fasting and in the afternoon while consuming six small test meals. Patients were also studied during two separate dialysis sessions (HDϩ protocol). Patients were fasted during one and consumed the meals during the other. Whole body protein metabolism was studied by primed constant infusion of L-[1-13 C]valine. During HDϪ, feeding changed the negative whole body protein balance observed during fasting to a positive protein balance. Dialysis deepened the negative balance during fasting, whereas feeding during dialysis induced a positive balance comparable to the HDϪ protocol while feeding. Plasma valine concentrations during the studies were correlated with whole body protein synthesis and inversely correlated with whole body protein breakdown. We conclude that the consumption of a protein-and energy-enriched meal by CHD patients while dialyzing can strongly improve whole body protein balance, probably because of the increased amino acid concentrations in blood. protein turnover; stable isotope; valine SIGNS OF PROTEIN ENERGY MALNUTRITION occur frequently in patients with chronic renal failure (17, 19). Protein energy malnutrition has been shown to be a major risk factor for increased morbidity and mortality in the chronic hemodialysis (CHD) patient (2, 17). Multiple factors predispose CHD patients to protein energy malnutrition, e.g., low caloric intake, low protein intake, and the hemodialysis procedure itself. Particularly, losses of amino acids or abnormal protein metabolism during hemodialysis might contribute to the observed protein energy malnutrition. Studies examining the role of CHD itself on protein metabolism are limited (22). Several lines of evidence indicate that the CHD procedure can result in a negative whole body protein balance. Nitrogen balance has been shown to be more negative on a dialysis day compared with a nondialysis day regardless of daily protein intake (5, 23). Lim et al. (22) studied whole body protein metabolism by applying the [ 13 C]leucine isotope dilution technique in fasting CHD patients during hemodialysis. They observed a reduction in whole body protein synthesis compared with the predialysis period, and this resulted in a doubling of the negative protein balance already present in fasting CHD patients. Furthermore, hemodialysis stimulates muscle protein losses compared with the predialysis period in fasting CHD patients (18).In apparently healthy subjects, the...

Background: This study investigated the agreement between various dried blood spot (DBS) and venous blood sample measurements of phenylalanine and tyrosine concentrations in Phenylketonuria (PKU) and Tyrosinemia type 1 (TT1) patients. Study design: Phenylalanine and tyrosine concentrations were studied in 45 PKU/TT1 patients in plasma from venous blood in lithium heparin (LH) and EDTA tubes; venous blood from LH and EDTA tubes on a DBS card; venous blood directly on a DBS card; and capillary blood on a DBS card. Plasma was analyzed with an amino acid analyzer and DBS were analyzed with liquid chromatography-mass spectrometry. Agreement between different methods was assessed using Passing and Bablok fit and Bland Altman analyses. Results: In general, phenylalanine concentrations in LH plasma were comparable to capillary DBS, whereas tyrosine concentrations were slightly higher in LH plasma (constant bias of 6.4 μmol/L). However, in the low phenylalanine range, most samples had higher phenylalanine concentrations in DBS compared to LH plasma. Remarkably, phenylalanine and tyrosine in EDTA plasma were higher compared to all other samples (slopes ranging from 7 to 12%). No differences were observed when comparing capillary DBS to other DBS. Conclusions: Overall agreement between plasma and DBS is good. However, bias is specimen-(LH vs EDTA), and possibly concentration-(low phenylalanine) dependent. Because of the overall good agreement, we recommend the use of a DBS-plasma correction factor for DBS measurement. Each laboratory should determine their own factor dependent on filter card type, extraction and calibration protocols taking the LH plasma values as gold standard.

BackgroundCongenital disorders of glycosylation (CDG) are a growing group of rare genetic disorders. The most frequently used screening method is sialotransferrin profiling using isoelectric focusing (IEF). Capillary zone electrophoresis (CZE) may be a simple and fast alternative. We investigated the Capillarys™ CDT assay (Sebia, France) to screen for N-glycosylation disorders, using IEF as gold standard.MethodsIntra- and inter-assay precision were established, and analyses in heparin-anticoagulated plasma and serum were compared. Accuracy was assessed by comparing IEF and CZE profiles of 153 samples, including 49 normal, 53 CDG type I, 2 CDG type II, 1 combined CDG type I and type II and 48 samples with a Tf-polymorphism. Neuraminidase-treated plasma was analysed to discriminate CDG and Tf-polymorphisms using samples of 52 subjects (25 had a confirmed Tf-polymorphism). Age-dependent reference values were established using profiles of 312 samples.ResultsHeparin-plasma is as suitable as serum for CDG screening with the Capillarys™ CDT assay. The precision of the method is high, with a limit of quantification (LOQ) of 0.5%. All profiles, including CDG and Tf-polymorphisms, were correctly identified with CZE. Forty-nine of 52 neuraminidase-treated samples correctly identified the presence/absence of a Tf-polymorphism. Interferences in 3/52 samples hampered interpretation. Sialo-Tf profiles were dependent of age, in particular in the first three months of age.ConclusionsCZE analysis with the Capillarys™ CDT kit (Sebia) is a fast and reliable method for screening of N-glycosylation defects. Tf-polymorphisms could be excluded after overnight incubation with neuraminidase.

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