Instability of fibroblast growth factor-23 (FGF-23): implications for clinical studies.

Background: Fibroblast growth factor-23 (FGF-23) is a bone secreted hormone that regulates phosphate homeostasis and calcitriol levels. FGF-23 concentrations are elevated in chronic kidney disease (CKD), oncogenic osteomalcia and a number of rare hereditary disorders. Studies systematically evaluating the pre-analytical stability of intact FGF-23 are lacking.

Poor agreement between commercial ELISAs for plasma fetuin-A: An effect of protein glycosylation?

Background: Fetuin-A is a circulating inhibitor of ectopic calcification. Low plasma levels have been associated in some studies with increased vascular calcification, aortic stiffness and mortality in patients with Chronic Kidney Disease (CKD). However, there are other studies examining the association of fetuin-A with vascular parameters and mortality, which do not show these associations.

Arginine and methylated arginines in human plasma and urine measured by tandem mass spectrometry without the need for chromatography or sample derivatisation.

A method for the simultaneous analysis of asymmetric dimethylarginine, symmetric dimethylarginine, monomethylarginine and arginine in human plasma and urine, with short analysis time and isotopic internal standardisation for each analyte is described. The method requires neither sample derivatisation nor the need for chromatographic separation of analytes. The method described shows good precision and accuracy and is suited for both research purposes and implementation in the busy, routine clinical laboratory.

Simultaneous quantitation of homocysteine, cysteine and methionine in plasma and urine by liquid chromatography-tandem mass spectrometry.

Background: A method utilizing liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS) has been developed and evaluated for the determination of total homocysteine, cysteine and methionine in plasma and urine. The simultaneous measurement of homocysteine and methionine concentrations may help explain the underlying mechanism responsible for hyperhomo-cysteinaemia.

Methods: Samples were prepared by simple protein precipitation after reduction of disulphides by dithiothreitol.