Myostatin propeptide mutation of the hypermuscular mice decreases the formation of myostatin and improves insulin sensitivity.

The TGFβ family member myostatin (growth/differentiation factor-8) is a negative regulator of skeletal muscle growth. The hypermuscular mice carry the 12-bp deletion in the sequence encoding the propeptide region of the precursor promyostatin, and additional modifier genes of the genetic background contribute to determine the full expression of the phenotype. In this study, by using mice strains carrying mutant or wild-type myostatin alleles with the genetic background and nonmutant myostatin with the wild-type background, we studied separately the effect of the mutation or the genetic background on morphology, metabolism, and signaling.

Procedure for determination of immunosuppressive drugs in whole blood with liquid chromatography-isotope dilution mass spectrometry.

Background: Cyclosporin A, sirolimus, tacrolimus, and everolimus are immunosuppressive drugs used for therapy after organ transplantation. There are several analytical procedures for monitoring the drug level in blood, e.g.

Diabetes mellitus: the long way of standardization of HbA(1c) to the level of highest metrological order.

Glycated haemoglobin (HbA(1c)) measurements are used in clinical studies and for the management of diabetic patients. Various efforts were made to standardize the HbA(1c) measurements with consensus standards and standards based on a reference measurement procedure with external calibration. According to ISO 17511 a standard should meet highest accuracy possible, have a defined uncertainty of measurement and the calibration should be traceable to SI units.

Liquid chromatography-isotope dilution-mass spectrometry as a new basis for the reference measurement procedure for hemoglobin A1c determination.

Background: Standardization of hemoglobin (Hb)A(1c) measurements is a process of considerable interest for quality assurance in diabetes management. To contribute to continuous quality improvement and fulfillment of the requirements for reference measurement procedures according to the standards of the International Organization for Standardization, we developed a calibration system of highest metrological order using isotope dilution-mass spectrometry with a reference material.

Method: Samples were prepared by enzymatic cleavage based on the IFCC reference measurement procedure for LC-MS analysis.

The alkaline haematin detergent (AHD575) method for the determination of haemoglobin in blood--a candidate reference measurement procedure.

The article describes the development and evaluation of the alkaline haematin detergent (AHD575) method for the determination of haemoglobin in blood without the need for toxic materials and suitable for use in laboratories in countries with limited resources and restricted import of toxic materials. The validation of the method has been performed in accordance with the requirements set out in the international standard ISO 15193, which describes the procedures necessary for development of a candidate reference measure-ment procedure. The main results were: The trueness of the haemiglobin cyanide (HiCN) method depends upon the diluent used.

Modified HPLC-electrospray ionization/mass spectrometry method for HbA1c based on IFCC reference measurement procedure.

Background: Monitoring of hemoglobin A(1c) (HbA(1c)) is important in the management of diabetes. The IFCC reference measurement procedure for HbA(1c) is based on the ratio of glycated to nonglycated N-terminal hexapeptides of the beta-chains of hemoglobin after digestion with Glu-C endoproteinase. We developed a modification of the original reference measurement procedure with HPLC-electrospray ionization/mass spectrometry (ESI/MS).

The IFCC Reference Measurement System for HbA1c: a 6-year progress report.

Background: The IFCC Reference Measurement System for hemoglobin (Hb)A(1c) (IFCC-RM) has been developed within the framework of metrologic traceability and is embedded in a network of 14 reference laboratories. This paper describes the outcome of 12 intercomparison studies (periodic evaluations to control essential elements of the IFCC-RM).

Methods: Each study included: unknown samples (to test individual network laboratories); known samples (controls); recently manufactured calibrators (to check calculated assigned value); stored calibrators (to test stability) and a calibration-set (to calibrate the IFCC-RM).

Global standardization of glycated hemoglobin measurement: the position of the IFCC Working Group.

The measurement of glycated hemoglobin is central in the monitoring of glycemic control in patients with diabetes. There are at least 30 different laboratory assays commercially available to measure the proportion of HbA1c in blood. In 1995 the IFCC established a Working Group (IFCC WG-HbA1c) to achieve international standardization of HbA1c measurement.

External quality assessment schemes in coagulation in Germany: between regulatory bodies and patient outcome.

In the early 1980s, the first external quality assessment schemes (EQAS) regarding parameters of the coagulation laboratory were established in the daily routine of German laboratories. At present, the EQAS performed by INSTAND offers a wide range of global and single parameters of thrombosis and hemostasis. Only the participation in prothrombin time and activated partial thromboplastin time exercises is mandatory.

A novel LC-IDMS/MS method for the determination of the cardiac glycosides digoxin and digitoxin using caesium adducts.

This article describes an essential improvement of the published candidate reference measurement procedure for digoxin and digitoxin and compares it with the original method. The novelty of the method lies in the measurement of the caesium (Cs+) ion as product ion in the multiple reaction monitoring mode (MRM) with potentially improved analytical specificity whilst retaining a comparable accuracy and precision at therapeutic levels. The original measurement procedure used the single-ion mode (SIM).

Modification of the IFCC reference measurement procedure for determination of HbA 1c by HPLC-ESI-MS.

The reference measurement procedure for determination of HbA(1c) (glycated haemoglobin) using HPLC(high performance liquid chromatography)-ESI(electrospray ionisation)-MS(mass spectrometry) has been modified. Main modifications were a change in the buffer composition of the HPLC, a change in the gradient elution profile and the introduction of a post-column splitting system. The long-term stability of the HPLC-ESI-MS system proved to be of high importance to get reproducible results.

A new approach for the determination of immunosuppressive drugs using HPLC-MS/MS and Cs+ adducts.

In this study a new principle of measurement in LC-MS/MS (liquid chromatography mass spectrometry) for determination of the immunosuppressive drugs sirolimus, everolimus, tacrolimus, and cyclosporin A has been introduced by using the Cs(+) ion as the product ion in the multiple reaction monitoring mode (MRM). Separation of the immunosuppressive agents was achieved using a phenyl-hexyl-RP column together with a ternary gradient elution profile, consisting of water, methanol and acetonitrile combined with 0.1% v/v formic acid and 0.

The performance of quantitative D-dimer assays in laboratory routine.

Assessment of D-dimer in plasma is routinely used for the exclusion of venous thrombosis and the monitoring of hypercoagulability. Little information is available about the performance of D-dimer assays in clinical laboratories examined by external quality assessment schemes. We obtained results from 423 laboratories measuring plasma pools from patients with elevated D-dimer levels mixed with human normal plasma.

External quality assessment of tumour marker analysis: state of the art and consequences for estimating diagnostic sensitivity and specificity.

This review shows the current analytical quality for the following analytes used as tumour markers in the external quality assessment (EQA)-programmes of Instand e.V., a national EQA-organiser in Germany: Corticotropin (ACTH), growth hormone (GH, hGH), prolactin (PRL), chorionic gonadotropin (CG, hCG), calcitonin (CT, hCT), thyroglobulin (Tg), carcinoembryonic antigen (CEA), CA-Antigens 125, 72-4, 15-3 and 19-9, alpha foetoprotein (AFP) and prostate-specific antigen (PSA).

Comparability of method results and performance in a national external quality assessment scheme between 1993 and 2003 using thyroid associated analytes as examples.

Six thyroid analytes (free and total triiodothyronine and thyroxine, thyrotropin and thyroglobulin) have been followed up over a 10 year period in a national external quality assessment scheme (EQAS) organised by the Institute for Standardisation and Documentation in the Medical Laboratory (INSTAND). I. The following points were observed: II.

Determination of the cardiac glycosides digoxin and digitoxin by liquid chromatography combined with isotope-dilution mass spectrometry (LC-IDMS)--a candidate reference measurement procedure.

This article describes a method of high analytical sensitivity, reproducibility and trueness for the determination of digoxin and digitoxin in serum or plasma at therapeutic levels using a combination of high-pressure liquid chromatography (HPLC), isotope-dilution mass spectrometry (IDMS) and caesium-adduct formation. A method for threefold deuterium substitution in the glycosides was developed, which could be performed within 24 hours without distillation giving yields > 98% of the theoretical value. Extraction from a serum or plasma matrix was performed using a liquid-phase extraction with ammonium acetate buffer/tertiary butylmethyl ether/ethyl acetate at pH 9.

Experience with an external quality assessment programme for point-of-care-testing (POCT) devices for the determination of blood glucose.

This article describes the preparation and internal and external evaluation of materials, critical issues in the external quality assessment (EQA) of point-of-care testing (POCT) devices for measuring blood glucose. A comparison was made between different materials, both of natural and synthetic origin and with and without stabilisers. The aims were to produce a material which was compatible with as many POCT-devices as possible and so reduce the number of materials sent out in each campaign as well as to optimise the precision and comparability of results between methods and devices.

Multicenter evaluation of a new immunoassay for intact PTH measurement on the Elecsys System 2010 and 1010.

Background And Objective: The determination of parathyroid hormone (PTH) is of great clinical relevance in the assessment of calcium metabolic disorders. Although PTH was one of the first hormones measured by immunoassays, there are still many difficulties in its determination due to the low concentration of the hormone in blood and due to the heterogeneity of PTH resulting from different circulating hormone fragments. The aim of our multicenter-study was to evaluate the technical performance and the clinical validity of a new immunoassay for intact PTH measurement on the Elecsys Systems 2010 and 1010.