Metanephrines, free (plasma)

Dietary precautions: Do not consume foods high in catecholamine and tyrosine for at least 12 hours – preferably three days – before a blood sampling (elevated 3-methoxythyramine level). These include: Caffeinated drinks, bananas, pineapple, fruit juices, nuts, tomatoes, potatoes, beans, alcohol, muesli, chocolate, tea, avocado, foods containing vanilla, liquorice, hard cheese and wine. If possible and provided that this is compatible with the therapy, medication that affects metanephrine level should not be taken for approx. one week before a blood sampling. Medication and substances which raise the level of metanephrine are: Tricyclic antidepressants, MAO inhibitors, carbidopa, levodopa, nitroglycerin, theophylline, tetracycline, sympathomimetics (alpha-adrenoreceptor agonists, amphetamines, cocaine, ephedrine), phenoxybenzamine, smoking. Medication and substances that lower the level of the metanephrines are: Reserpin, alpha-methyl-p-tyrosine. Low values can also be caused by an angiography having been performed previously. | For plasma determinations, the following standard conditions are recommended: recumbent patient, put venous cannula into forearm. Keep cannula open by injection of small amounts of physiological saline at 5 min intervals (rinsing with sterile saline at 5 min-intervals may be replaced by injection of heparin). After at least 15 min: withdraw 10 mL blood without venous stasis into 2 EDTA- or Li-heparin tubes (after having discarded 1 – 2 tubes). Immediately put tubes on ice, centrifuge at 0 – 4 °C within 30 min. and pipet plasma into 2 tubes without additive (2 – 2.5 mL). Store plasma samples and then transport at -20°C. | May not be requested from stored sample.