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. Patients with neuroblastic disease were further classified as untreated, advancing, residual or absent disease based on clinical and radiological criteria. Receiver operating characteristic curve analysis was used to compare the diagnostic performance of the four tumour markers. Results Urinary 3-methoxytyramine was well correlated with established tumour markers and its concentration correlated with disease activity. It was the most commonly elevated tumour marker in neuroblastic disease and showed similar sensitivity to dopamine and homovanillic acid. The diagnostic utility of urinary 3-methoxytyramine as measured by area under the receiver operating characteristic curve was similar to dopamine and homovanillic acid. Conclusion Our results support the use of urinary 3-methoxytyramine as a tumour marker in the diagnosis and the monitoring of neuroblastoma disease.

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. The results were higher in contrast to plasma measurements on the Abbott Architect Ci8200, which were within reference intervals and in line with the patient's pathophysiological status. This indicated a likely interference with the blood gas analyser chloride estimation. The chloride results on the ABL800 for 3rd, 4th and 5th day after the burn accident were 170, 137 and 119 mmol/L. Corresponding plasma chloride results on the Ci8200 were all around 105 mmol/L. Nitrate was found to be markedly elevated in these samples, and the results were 6.7, 4.9 and 1.1 mmol/L, respectively (reference limit < 0.08 mmol/L). To further demonstrate nitrate was the causative agent, pooled plasma spiked with 7 mmol/L of sodium nitrate caused a rise in the ABL800 chloride from 105 to 202 mmol/L. Later we confirmed that the patient was topically medicated with cerium nitrate cream (Flammacerium®, Sinclair IS Pharma, UK) for his burns. In summary, the results clearly indicated nitrate was the interferent with the ABL800 chloride estimation and the source was the topical burns cerium nitrate cream.

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. METHODS: The interference had identical chromatographic and electrochemical properties to the Recipe(®) internal standard (undisclosed identity). Inspection of the patient names showed it seemingly had a higher frequency and magnitude in patients of Indian origin. The source of the interference was tracked by dietary observation and intervention to curry leaves, a common component of Indian foods. RESULTS: The interference was chromatographically and electrochemically indistinguishable from the internal standard. The mass spectrum of the pentafluoropropionate derivative of the interference matched the Recipe(®) internal standard and was identified as methoxyhydroxybenzylamine by library match. CONCLUSION: The component co-elutes exactly with internal standard and artifactually decreases the metanephrine and normetanephrine results. It is surprising that it has not been described previously. Patients being assessed for catecholamine secreting tumours should be advised to withdraw from eating Indian foods at least 24 h prior to commencement of urinary collection.

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. This best practice guideline has been developed with reference to the Centers for Disease Control and Prevention (CDC) "Laboratory Medicine Best Practices: Developing an Evidence-Based Review and Evaluation Process". The CDC document cites an evaluation framework for generating best practice recommendations that are specific to laboratory medicine. These 50 recommendations proposed herein, were generated from a comprehensive literature search and the extensive combined experience of the AACB Vitamins Working Party members. They were formulated based on comparison between an impact assessment rating and strength of evidence and were classified as either: (1) strongly recommend, (2) recommend, (3) no recommendation for or against, or (4) recommend against. These best practice recommendations represent the consensus views, in association with peer reviewed evidence of the AACB Vitamins Working Party, towards best practice for the collection, analysis and interpretation of vitamins A, E and carotenoids in blood.

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, ß-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. DESIGN AND METHODS: A questionnaire was sent to thirteen laboratories. Eleven laboratories were returning QAP results for vitamin B1 (thiamine diphosphate) and five were returning results for vitamin B6 (pyridoxal-5-phosphate). RESULTS: All nine respondents provided a clinical service for vitamins B1 and B6. HPLC with fluorescence detection was the most common method principle. For vitamin B1, six respondents used a commercial assay whilst three used in-house methods; whole blood was the matrix for all. For vitamin B6, five respondents used commercial assays and four used in-house assays. The choice of matrix for vitamin B6 varied with three respondents using whole blood and five using plasma for analysis. Sample preparation incorporated protein precipitation and derivatization steps. An internal standard was employed in sample preparation by only one survey respondent. CONCLUSIONS: The immediate result of this survey was the incorporation of plasma vitamin B6 into the RCPA QAP vitamin program. The absence of an internal standard in current vitamin B1 and B6 assays is a likely contributor to the wide dispersion of results seen in this program. We recommend kit manufacturers and laboratories investigate the inclusion of internal standards to correct the variability that may occur during processing.

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. During normoxia, control and nicotine-exposed P0 mice exhibited a high frequency of apnoea (f(A)) which declined by P3 in control animals (from 6.7 +/- 0.7 to 2.2 +/- 0.7 min(-1)) but persisted in P3 nicotine-exposed animals (5.4 +/- 1.3 min(-1)). Hypoxia induced a rapid and sustained reduction in f(A) except in P0 nicotine-exposed animals where it fell initially and then increased throughout the hypoxic period. During recovery, f(A) increased above control levels in both groups at P0. By P3 this increase was reduced in control but persisted in nicotine-exposed animals. To examine the origin of differences in respiratory behaviour, we compared the activity of hypoglossal (XII) nerves and motoneurons in medullary slice preparations. The frequency and variability of the respiratory rhythm and the envelope of inspiratory activity in XII nerves and motoneurons were indistinguishable between control and nicotine-exposed animals. Activation of postsynaptic nicotine receptors caused an inward current in XII motoneurons that potentiated XII nerve burst amplitude by 25 +/- 5 % in control but only 14 +/- 3 % in nicotine-exposed animals. Increased apnoea following nicotine exposure does not appear to reflect changes in basal activity of rhythm or pattern-generating networks, but may result, in part, from reduced nicotinic modulation of XII motoneurons.