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.

Evaluation of serum neopterin, high-sensitivity C-reactive protein and thiobarbituric acid reactive substances in Egyptian patients with acute coronary syndromes.

The present study evaluated serum neopterin, high-sensitivity C-reactive protein (hs-CRP) and thiobarbituric acid reactive substances (TBARS) in Egyptian patients with acute coronary artery disease. Thirty-six patients with unstable angina aged (mean +/- SD) 61.3+/-9.

Direct measurement of low density lipoprotein in whole blood by silver-enhanced gold-labelled immunoassay.

A competitive silver-enhanced gold-labelled immunoassay has been developed for the direct measurement of low density lipoprotein (LDL) in whole blood. Immobilized LDL and sample LDL compete for added antibody. Quantitation of the bound antibody/antigen complex is achieved by the addition of gold-labelled anti-immunoglobulin G followed by enhancement of absorbance by addition of silver ions.

Multiple releasable fluorescein labels for immunoassay: the principle illustrated by an immunoassay for antibodies to the human immunodeficiency virus.

Attempts to increase the sensitivity of fluorescein-based fluorescence immunoassays by using multiple labelling have generally been unsuccessful because of concentration quenching. We have labelled antibodies to human immunoglobulin G with multiple fluorescein fluorophores attached by means of a disulphide linkage: this linkage can be rapidly and easily broken by treatment with dithiothreitol, allowing fluorescein to be released from the antibody and measured in free solution. Application of this technique to a fluorescence labelled immunosorbent assay for antibodies to the human immunodeficiency virus gave an approximately 20-fold increase in signal compared with an equivalent assay using fluorescein isothiocyanate.

A silver enhanced, gold labelled, immunosorbent assay for detecting antibodies to rubella virus.

A silver enhanced, gold labelled, immunosorbent assay (SEGLISA) for the detection of IgG antibodies to the rubella virus in human serum was developed. Pre-coated microtitre wells are used as the immobilised base of rubella antigens on to which any rubella antibodies from patient samples will bind. This antigen/antibody complex is then visualised firstly by gold labelled anti-immunoglobulin G, which binds to any human IgG that may be present, and then by silver amplification, resulting in a black permanent deposit on the microtitre well surface.

Use of a silver-enhanced gold-labelled immunoassay for detection of antibodies to the human immunodeficiency virus in whole blood samples.

A silver-enhanced gold-labelled immunosorbent assay (SEGLISA) for the detection of antibodies to the immunodeficiency virus (HIV) in whole-blood samples is described. This new non-isotopic, non-enzymic immunoassay incorporates use of solid phase viral antigens which bind any HIV antibodies present in the test sample. The antigen/antibody complex is then detected by gold-labelled anti human immunoglobulin G (IgG) followed by silver amplification.

Detection of antibodies to the human immunodeficiency virus by a silver-enhanced gold-labelled immunosorbent assay.

We describe a new immunoassay for the detection of antibodies to the human immunodeficiency virus. The method is based on a silver enhanced gold-labelled immunosorbent assay (SEGLISA). Test sera are incubated in microtitre wells on which antigens have been coated.

Multiple labelling of immunoglobulin G, albumin and testosterone with a fluorescent terbium chelate for fluorescence immunoassays.

Human immunoglobulin G, human serum albumin and testosterone were labelled with the 4-aminosalicylic acid derivative of diethylenetriaminepentaacetic acid complexed with terbium ions. An exceptionally large amount of label, of the order of a few hundred moles of complex per mole of analyte, could be conjugated to the compounds tested by the use of poly-L-lysine. Self-quenching appears to be minimal, even with this high local concentration of fluorophores.

Detection of antibodies to the human immunodeficiency virus by a rapid fluorescence-labelled immunosorbent assay.

The development and assessment of a fluorescence-labelled immunosorbent assay for the detection of antibodies to the human immunodeficiency virus is described. Test serum is incubated in microtitre wells on which antigens have been coated. If present in the test serum, antibodies to the human immunodeficiency virus bind to the solid-phase antigens.

On the use of fluorescent labels in immunoassay.

The principles and use of fluorescent labels in immunoassay are reviewed. Comparison is made with radio- and chemiluminescent immunoassays. Possible fluorescent labels are listed.

Determination of plasma cytidine deaminase activity by HPLC.

Cytidine deaminase is an enzyme of nucleic acid metabolism, the measurement of which has been proposed as a useful test for the early detection of pre-eclamptic toxaemia in pregnancy. The enzyme converts the nucleoside cytidine to uridine, with the release of ammonia, and it is the measurement of this latter compound that forms the basis of the conventional methods for the assay of cytidine deaminase. The low activity of the enzyme requires long incubation times, which in turn increase the possibility of contamination by exogenous ammonia.

Magnesium and the premenstrual syndrome.

Plasma and erythrocyte magnesium were measured in 105 patients with premenstrual syndrome (PMS) using a simple atomic absorption spectroscopy method. The erythrocyte magnesium concentration for the patients with PMS was significantly lower than that of a normal population. The plasma magnesium did not show this difference.

Whole blood osmolality.

The osmolality of plasma and heparinised whole blood samples collected from hospital patients was estimated using measurement of the depression of freezing point. There was no clinically significant difference between osmolality measurement made on either whole blood, or plasma taken from the same patient. Neither cell volume nor haemolysis was found to affect the measurement.

Hypomagnesium in the elderly.

The range of plasma concentrations in 177 and erythrocyte magnesium concentrations in 104 elderly patients was found to be similar to that for healthy adults. No significant difference was observed between the sexes or between patients taking diuretics and those not receiving diuretic therapy. The latter finding is contrary to some previously reported studies.