Quality assurance programs for vitamin A and E in serum: are we doing enough to assess laboratory performance?

Objectives: Monitoring serum vitamin A (retinol) and vitamin E (α-tocopherol) concentrations is common practice for assessing nutritional status. Measurement of these vitamins can be challenging due to several factors. Whilst the RCPAQAP Vitamins: Serum Program assists participating laboratories in harmonisation, the materials provided do not contain the analogues of retinol and α-tocopherol that may be present in real patient samples.

Harmonization of LC-MS/MS Measurements of Plasma Free Normetanephrine, Metanephrine, and 3-Methoxytyramine.

Background: Plasma-free normetanephrine and metanephrine (metanephrines) are the recommended biomarkers for testing of pheochromocytoma and paraganglioma (PPGL). This study evaluated the status of harmonization of liquid chromatography-tandem mass spectrometry-based measurements of plasma metanephrines and methoxytyramine and clinical interpretation of test results.

Methods: 125 plasma samples from patients tested for PPGLs were analyzed in 12 laboratories.

Falsely elevated plasma metanephrine in patients taking midodrine.

Plasma metanephrines have become the biochemical test of choice for suspected phaeochromocytomas and paragangliomas in many institutions. We encountered two separate cases of significantly elevated plasma metanephrines in patients taking midodrine, a sympathomimetic drug used in the treatment of severe postural hypotension, in the absence of a diagnosis of phaeochromocytomas and paragangliomas. Upon stopping midodrine treatment, plasma metanephrine concentrations returned to normal in both patients.

Clinical validation of urine 3-methoxytyramine as a biomarker of neuroblastoma and comparison with other catecholamine-related biomarkers.

Background Urinary dopamine, homovanillic acid and 4-hydroxy-3-methoxymandelic acid are established tests for diagnosis and monitoring of neuroblastic disease. We compared the diagnostic performance of total urinary 3-methoxytyramine, the O-methylated product of dopamine, to these three established tumour markers. Methods Urinary 3-methoxytyramine, dopamine, homovanillic acid and 4-hydroxy-3-methoxymandelic acid were measured by high-performance liquid chromatography with electrochemical detection on consecutive urine samples from histologically proven neuroblastic patients and controls.

Falsely raised whole blood chloride caused by systemic absorption of cerium nitrate cream for burns.

Whole blood, serum or plasma chloride is almost exclusively measured by potentiometry with an ion-selective chloride electrode which utilizes membrane selectivity to chloride ions. Other anions such as bromide, iodide and thiosulphate can interfere but usually are not present in high enough concentration to cause significant cross reactivity. A patient from our burns unit had serial chloride measurements on a Radiometer ABL800 blood gas analyser.

Laboratory medicine best practice guideline: vitamins a, e and the carotenoids in blood.

Despite apparent method similarities between laboratories there appear to be confounding factors inhibiting uniform reporting and standardisation of vitamin assays. The Australasian Association of Clinical Biochemists (AACB) Vitamins Working Party, in conjunction with The Royal College of Pathologists of Australasia Quality Assurance Programs, has formulated a guideline to improve performance, reproducibility and accuracy of fat-soluble vitamin results. The aim of the guideline is to identify critical pre-analytical, analytical and post-analytical components of the analysis of vitamins A, E and carotenoids in blood to promote best practice and harmonisation.

Interference from Indian diet on the internal standard in a commercial method for the measurement of urinary metanephrines by high-performance liquid chromatography with electrochemical detection.

Introduction: Urinary metanephrines are widely used in the diagnosis of catecholamine secreting tumours. Over the past two years we have been using the commercial Recipe(®) ClinRep(®) Complete Kit for Metanephrines in Urine coupled with high-performance liquid chromatography and coulometric detection. It was noticed that the internal standards on the patient chromatograms were sporadically raised due to interference.

Vitamin B1 and B6 method harmonization: comparison of performance between laboratories enrolled in the RCPA Quality Assurance Program.

Objectives: The RCPA Quality Assurance Program (RCPA QAP) offers monthly proficiency testing for vitamins A, B1, B6, β-carotene, C and E to laboratories worldwide. A review of the results submitted for the whole blood vitamin B1/B6 sub-program revealed a wide dispersion. Here we describe the results of a methodology survey for vitamins B1 and B6.

Serum vitamin A and E analysis: comparison of methods between laboratories enrolled in an external quality assurance programme.

Aim: To survey laboratories enrolled in the Royal College of Pathologists of Australasia (RCPA) Chemical Pathology Quality Assurance Programme (QAP) for vitamin A and E testing to determine differences between methods of analysis.

Methods: A detailed questionnaire covering the major aspects of serum vitamin A and E analysis was sent to all participating laboratories in 2007.

Results: Thirteen out of the 22 laboratories completed the questionnaire.

An evaluation of the Abbott IMx sirolimus assay in relation to a high-performance liquid chromatography-ultraviolet method.

Background: Sirolimus is an immunosuppressive agent used after organ transplantation. Monitoring its concentration is clinically relevant, but current methods of measurement using high-performance liquid chromatography (HPLC) are demanding. An immunoassay that uses readily available equipment offers a more convenient alternative.

Prenatal nicotine exposure increases apnoea and reduces nicotinic potentiation of hypoglossal inspiratory output in mice.

We examined the effects of in utero nicotine exposure on postnatal development of breathing pattern and ventilatory responses to hypoxia (7.4 % O2) using whole-body plethysmography in mice at postnatal day 0 (P0), P3, P9, P19 and P42. Nicotine delayed early postnatal changes in breathing pattern.