Urine free catecholamines

Earlier fluorometric methods for analysis of urinary free catecholamines have been replaced by HPLC methods that allow selective quantitation of epinephrine, norepinephrine, and dopamine. Preliminary extraction of urine is stid required and numerous preanalytical cleanup techniques are available. An alumina extraction procedure is typically coupled with ion-exchange or adsorption chromatography. Alumina pretreatment usually involves a batch extraction technique in which catechols are first adsorbed at pH 8.6 and then eluted with boric acid, which forms a complex with cis-diol groups. Purification on boric acid affinity gels provides an alternative procedure for selective adsorption of catecholamines. 

Premel-Cabic A, Turcant A, AUain P. Normal reference intervals for free catecholamines and their add metabolites in 24-h urines from children, as determined by liquid chromatography with amperometric detection. Clin Chem 1986 32 1585-7. 

Eiquid- or solid-phase extraction methods have been adopted for the isolation of catecholamines and their metabolites from urine samples. The liquid extraction system is ordinarily based on the formation of a complex, in alkaline medium, between diphenylborate and the diol group in the catecholamines. However, the liquid extraction methods reported in the literature are relatively tedious and often involved multiple extraction steps.For the more widely used solid-phase extraction methods, catecholamines may be selectively isolated from the urine sample by adsorption with activated alumina," " phenylboronic acid or cation-exchange resins. All the specimen preparative procedures are specific for the free catecholamines, i.e. the extracted catecholamines do not include the conjugated fraction. 

F. Boomsma, G. Alberts, F.A. van der Hoorn, A.J. Man in t Veld and M.A.D.H. Schalekamp, Simultaneous determination of free catecholamines and epinine and estimation of total epinine and dopamine in plasma and urine by high-performance hquid chromatography with fluorimetric detection, J. Chromatogr, 51A, 109-117 (1992). 

The basis for the high diagnostic efficacy of plasma free metanephrines is explained by several factors (1) plasma free metanephrines are produced by metabolism of catecholamines within pheochromocytomas, a process that occurs continuously and independently of variations in catecholamine release by tumors (2) normally only small amounts of metanephrines are produced in the body, and these are relatively unresponsive to sympathoadrenal activation compared with the parent amines and (3) VMA and the metanephrines commonly measured in urine are different metabofites from the free metanephrines measured in plasma, and are produced in different parts of the body by metabolic processes not directly related to the tumor itself." ... 

Additional markers of catecholamine overproduction have been employed to improve the biochemical detection of neuroblastomas. Free dopamine may be abnormal in urine from neuroblastoma patients with VMA and HVA excretion. Combined testing for VMA, HVA, and dopamine may therefore improve tumor detection, and in 1993 an international consensus report on neuroblastoma diagnosis added dopamine to the Hst of acceptable measurements to document the adrenergic nature of the tumor. Plasma measurements of dopamine and L-dopa, the amino acid precursor of dopamine, may also have clinical value and allow the alternate use of plasma. Measurement of methylated metabolites, especially normetanephrine, has also been explored. When urinary normetanephrine, metanephrine, methoxytyra-mine, dopamine, norepinephrine, VMA, and HVA were measured, clinical sensitivity for detection of neuroblastomas was 97% to 100% when results of normetanephrine testing were coupled either with VMA in the infants or with HVA in children greater than age 1. Even with an extended panel of catecholamines and metabolite measurements, a low incidence of nonsecreting tumors continues to be identified and should be considered in the interpretation of a negative test result. 

Urinary catecholamines represent a quantitatively small but diagnostically important component of the catecholamine excretion products. Catecholamines are excreted in the urine as free amines and as glucuronide and sulfate conjugates. As with plasma measurements, total urinary catecholamines (conjugated and unconjugated forms) may be measured by... 

These challenges observed for both electiochemical and fluorimetric modes of detection prompted the need for a more sensitive, selective and maintenance-free HPLC assay for routine, rapid, simultaneous measurements of catecholamines and metanephrines in urine. 

J. Odink, H. Sandman and W.H.P. Schreurs, Determination of free and total catecholamines and salsolinol in urine by ion-pair reversed-phase liquid chromatography with electrochemical detection after a one step sample clean-up, J. Chromatogr, 311, 145-154 (1986). 

D8. Demassieux, S., Corneille, L., Lachance, S., and Carriere, S., Determination of free and conjugated catecholamines and L-3,4-dihydroxyphenyalanine in plasma and urine Evidence for a catechol-O-methyltransferase inhibitor in uraemia. Clin. Chim. Acta 115,377-390(1981). 

N-ACTYR is the neutral metabolite of TYR. N-ACTYR is excreted after conjugation with glucuronic acid and sulfate, and less than 0.2% is detected as free unchanged compound [39]. In neuroblastoma, elevated levels of catecholamines or its metabolites can be found in the urine, and urinary N-ACTYR was detected in these patients [40]. 

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