Normetanephrine/Metanephrine. To the Editor: Measurements of the excretions of normetanephrine and metanephrune in. 222. CLINICAL CHEMISTRY,. Vol.
urn heparin (3). Over a period from September to June, samples were consistently taken between 08:00 and 09:00 hours. Plasma magnesium (PMg) and calcium (P-Ca) were analyzed by flame atomic absorption spectrometry in a Hitachi Model 180-80 with Zeeman effect (2). Simple (r) correlation coefficients were estimated after the normality of the distribution was checked by the chi-square test. Test of significance of the simple correlation coefficient was performed by the t-test. The means and standard deviations for P-Mg were 0.77 (0.06) mmol/L in men and 0.77 (0.05) mmol/L in women. The results for P-Ca in the two populations were respectively 2.20 (0.12) mmol/L and 2.18 (0.10) mmol/L (2). In terms of the number of subjects involved, the simple correlation coeffident between P-Mg and P-Ca was not significant for men (r = -0.190, p >0.05) or women (r = +0.126, p >0.05). We were thus unable to conclude, as had other authors (1 ), that under normal physiological conditions magnesium and calcium are interrelated. Moreover, nonsignificant correlations between these two variables were found in our studies of insulin-dependent diabetics (19 men and 22 women) and of 10 noninsulin-dependent diabetic women (4). Results were similar for 26 men and 1 1 women with unstable angina pectoris (5). Studies in this field should, however, be continued in a longer series of subjects and without neglecting the influence of ecologic and genetic factors. It would also be advisable to carry out multivariate statistical analysis relative to a greater number of variables (multiple regression, multiple correlation). References 1. Turkungton VE, Nanji AA. Concentrations of Mg and Ca in serum are correlated in normal individuals. Clin Chem 1985;31:501-2.
2. Speich M, Gelot S, Arnaud P, Van Goc N, Robinet N, Pineau A. Multiple and simple correlations between magnesium, calcium, zinc, potassium, total- and HDL-cholesterol in 111
reference
CLINICAL CHEMISTRY,
Speich
A 3:5
Lab. de Biochimie Pharmaceutique UE1?. des Sciences Pharmaceutiques 1, rue Gaston Veil 44035-Nantes Ceder, France
P 25
-
S 2.0 .5 E
.0 05
LI as Exogenous Marker for Urine Volume
Determinations WEEKS
T6
YEARS
B
To the Editor: In a recent Letter, Ronquist et al. (1) advocate the use of LiC1 as an exogenous marker for determining or checking volumes of urine specimens. IfLi is measured by flame emission photometry, this is invalid because several ions interfere with such measurements, among them K. This interference is not found in serum (3), most probably because the K concentration is fairly constant as compared with that in urine. Using the FLM 3 flame emission photometer (Radiometer, Copenhagen) with K as internal standard, we have found K to greatly influence Li measurements. As seen from following tabulation of Li (1 mmol/L) measured in aqueous K’-contauning solutions, it is possible to underestimate the Li concentration by as much as 46% in the extreme range of urine K concentration; this is unacceptable in regard to accurate measurements of urine volumes. added, mmol/L Li’ found,
K
%
0 25 50 75 100 150 99847467 61 54
References 1. Eonquist G, Andereson G, Aim Y. Use of lithium to determine volume of 24-h urine specimens [Letter). Cliii Chem 1985; 31:1413-4. 2. Anidisen A. The estimation of lithium in urine.
In:
Johnson
FN,
ed.,
Lithium
re-
search and therapy. New York: Academic Press 1975:181-95. 3. Levy AL, Katz EM. Comparison of serum lithium determination by flame photometry and atomic absorption spectrophotometry. Cliii Chem 1970;16:840-2.
subjects. Magnesium-Bul-
letin 1984;6:137-41. 3. Speich M, Gelot S. Choice of a satisfactory evacuated blood-collection tube for magnesium and zinc assays. Clin Chem 19829:1560-1. 4. Speich M, Gelot S, Arnaud P, Murat A. Plasma and erythrocyte magnesium in insulin-dependent and non-insulin-dependent diabetics: correlations between twelve vanables. Magnesium-Bulletin. In press. 5. Speich M, Gelot S, Arnaud P, Robinet N, Nicolas G. Magnesium, calcium, zinc, potasslum, cholesterols total et HDL, cr#{233}atinekinase totale dana 37 cas d’angor instable: #{233}tude de correlations. Magnesium. In press. 222
Michelle
Carsten Dept. AaThorg DK-9000
E. Larsen
of Clin. Chem. Hospital Aalborg, Denmark
Pediatric Reference intervals Normetanephrine/Metanephrine
for
To the Editor: Measurements normetanephrine
Vol. 32, No. 1, 1986
of the excretions and metanephrune
of in
LJ
ii,.‘U-
0
5
I03
WEEKS
6
90 12 3 345
MONTHS
6 78 91011 121314e
YEARS
Fig. 1 Age-related values for the unnaiy excretion of (A) normetanephrine (mg/g cssatinine) and ( metanephrine (Lg/g creatinine) in a healthy pediatric population .
Shaded ±
a,eas
represerd reference intervals (mean
2 SD) for the vaflous
age
groups
urine may be useful in the diagnosis of neural crest tumors in neonates and pediatric patients. We determined reference ranges for the urinary excretion of these urinary catecholamune metabolitea in untiined urine specimens collected from neonates (several hours to 30 days after birth), infants (one to 11 months), and children (one to 15 years), all in apparent good health. Specimens were recovered from diapers of neonates and infants within several hours of voiding and obtained from children at visits to a pediatric clinic. Studies revealed complete analytical recovery of these metabolites and creatunune from urine samples added to a diaper. The methods used in measuring urinary normetanephrune, metanephrine, and creatunune have been previously described (1). Figure 1 shows, for four age groups, the individual values and the reference intervals for normetanephrine and methnephrine, both in terms of creatinine. Values differing by more than 3 SD from the mean were excluded from the reference interval calculation. The mean ± SD ofvalues for normetanephnine in neonates younger than two daysold(1.419 ± 0.44 mg/gcreatinine, n = 23) were significantly lower (p
