Reference intervals normetanephrine

Interpretation of a biochemical test result as normal or abnormal depends on availability of valid reference intervals (see Chapter 16). For tests of a single analyte, such as VMA, it can be expected that at least 2.5% of patients without pheochromocytomas will have values for the analyte above the upper reference limit and 2.5% below the lower reference limit. Up to a 5% incidence of false-positive results might be expected for tests of pairs of analytes, such as norepinephrine and epinephrine in tests of urinary or plasma catecholamines or normetanephrine and metanephrine in tests of plasma free or urinary fractionated metanephrines. False-positive rates usually, however, tend to be higher than expected this is likely due to reduced control over sampling conditions and sources of interference or differences in clinical characteristics of reference and patient populations. 

Reference intervals for plasma and urinary catecholamines and catecholamine metabolites also differ according to sex and age. Females have lower plasma concentrations of epinephrine and metanephrine than males. Similarly, 24-hour urinary outputs of catecholamines and metanephrines are lower in women than men for epinephrine this difference remains significant when values are normalized for creatinine excretion Plasma levels of norepinephrine and normetanephrine increase with advancing age in adults, whereas plasma levels of epinephrine and metanephrine are little affected. Age-related increases in 24-hour urinary outputs of norepinephrine and normetanephrine have also been reported,but not consistently by all studies. In general, the influences of age... 

Table 29-11 shows representative reference intervals for metanephrine and normetanephrine in children and adults. One-hour excretion of metanephrines has also been used in the detection of pheochromocytomas but diurnal variation in metanephrine excretion must be considered when short collection intervals are used. 

Canfell PC, Binder SR, Khayam-Bashi H. Pediatric reference intervals for normetanephrine/ metanephrine. Clin Chem 1986 32 222-3. 

Kairisto V, Koskinen P, Mattila K> Puilckonen J, Virtanen A, Kantola I, Irjala K. Reference intervals for 24-h urinary normetanephrine, metanephrine, and 3-methoxy-4-hydroxymandelic acid in hypertensive patients. Clin Chem 1992 38 416-20. 

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