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General Clinical Chemistry |
1
Servicio de Bioquímica Clínica, Hospital de Navarra, Iruñlarrea 3, 31008 Pamplona, Spain.
2
Servicio de Pediatría, Hospital Virgen del
Camino, 31008 Pamplona, Spain.
a Author for correspondence. Fax 34-948-422-303.
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Fat malabsorption is not an early finding in these syndromes, and other methods often identify the disorder before steatorrhea develops. Nevertheless, measurement of daily stool fat excretion is the most direct and accurate method of demonstrating fat malabsorption (3). Water content is also indispensable for assessing digestive functions and certain syndromes such as constipation and diarrhea (4). Protein malabsorption (measured as nitrogen excretion) can be found in many gastrointestinal diseases, and the evaluation of nitrogen balance is essential in the management of patients with nutritional problems (5) and in subjects with suspected protein maldigestion (6). Fecal carbohydrate loss measurement is also important in the diagnosis of malabsorption syndromes (7)(8), although certain amounts of starch are malabsorbed even under physiologic conditions (9).
Established and usual methods for the measurement of fecal water, fat, nitrogen, sugar, and starch are very unpleasant, labor-intensive, and time-consuming (10)(11)(12)(13). In recent years, a new method based on near-infrared reflectance spectroscopy (NIRRS) has presented an alternative for the development of the "fecalogram" that avoids cumbersome chemical techniques (5)(14)(15). Fecal analysis by NIRRS presents some advantages: it is very fast (1 min); it does not require reagents; and very little sample manipulation is necessary.
Determinations of the major nutrients in feces are of special interest for the diagnosis in infants of some of the pathologies mentioned above and for the evaluation of their diets. Adequate food intake and absorption is of great importance for the development of children, especially during the first year of life. Fat malabsorption, for example, is considered one of the major causes of poor growth in infancy.
The aim of this study was to obtain the reference intervals for nutrients such as water, fat, nitrogen, sugar, and starch in the feces of children.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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subjects
A total of 180 apparently healthy children from 20 days to 14
years of age were enrolled for the study after informed parental
consent was obtained. These children were both outpatients and
inpatients. The latter were included in the study after excluding
patients with any gastrointestinal disease. The children were divided
into four age groups established according to the different diets of
children:
group 1: 
6 months (n = 42);
group 2: 7–18 months (n = 46);
group 3: 19 months–4 years (n = 45); and
group 4: >4–14 years (n = 47).
Group 1 consisted of 15 females and 27 males; group 2 consisted of 18 females and 28 males; group 3 consisted of 18 females and 27 males; and group 4 consisted of 21 females and 26 males. Children ate their usual diets, which for group 1 was composed either of human milk or formula milk, supplemented with cereal, fruits, and vegetables in some cases. There were five breast-fed infants in this group.
Stools were collected in preweighed plastic containers for 24 h and carefully mixed manually immediately before measurement. Three small fecal samples were pressed in a disposable cup to give a smooth surface. The cup was then inserted into the instrument.
imprecision
The within-run CV of the analytical method was obtained from the
analysis of three or four samples 15 times each in one analytical run,
whereas the between-run CV was obtained from the analysis of a
different set of three or four samples one time in 15 different
analytical runs.
statistical analysis
Statistical analysis was performed according to the Expert Panel
on the Theory of Reference Values of the International Federation of
Clinical Chemistry (17).
To know if the studied populations had a gaussian distribution, we
applied the Anderson-Darling test and the skewness and kurtosis
coefficients. The fractiles and the estimated ß confidence intervals
were also calculated. When the populations did not have a gaussian
distribution, nonparametric statistics were used to obtain the
reference interval. Outliers were detected using the Dixon test
(18). Differences between the four groups were tested by
using the Kruskal–Wallis test (H statistic), with 
= 0.05 as the
threshold for statistical significance.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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summarizes the results of the within- and between-run
imprecision studies. As shown in Table 1
, the CVs were satisfactory,
except for those obtained for starch at low concentration (g/100 g).
Likewise, the between-run imprecision for starch and sugar was somewhat
high at 6.0 and 1.4 g/100 g, respectively. The lowest imprecision was
obtained for water concentration.
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reference intervals
When results were expressed as concentrations (g/100 g of feces),
all the substances except for starch followed a gaussian distribution.
The central 0.95 reference intervals in g/100 g for water, fat,
nitrogen, and sugar content, the 0.025 and 0.975 fractiles, and their
0.90 confidence intervals in the analyzed stools of the children are
given in Table 2
. The highest reference interval endpoint for fat was found in
group 1, for water in group 2, for nitrogen in group 3, and for sugar
in group 1.
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We would highlight the results for starch content. In the four groups, the medians (which were 10 g/100 g, 7.8 g/100 g, 10 g/100 g, and 10 g/100 g for groups 1, 2, 3, and 4, respectively) were practically the same as the 0.975 fractile. This phenomenon was due to the inability of the analyzer to read more than 10 g of starch/100 g of feces.
On the other hand, when results were expressed in output excretion
(g/day), all the substances had a non-gaussian distribution; these
results were analyzed using nonparametric statistics. Fecal weight was
highly variable: weights ranged from 5.00 to 67.74 g/day, 11.04 to
80.80 g/day, 5.6 to 175.69 g/day, and 12.5 to 147 g/day in groups
1, 2, 3, and 4, respectively. Reference intervals in g/day for each
nutrient are summarized in Table 3
, where 0.025 and 0.975 fractiles and the median are shown.
Significant differences were found between the groups for each
substance (P <0.005), using the Kruskal–Wallis test.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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OH, NH, and
CH functional groups. Most substances exhibit a characteristic
near-infrared spectrum, which enables their quantification. As
mentioned previously, NIRRS presents some major advantages: it is fast
(1 min), needs no reagents, and the analysis is performed without
additional processing of the stools (16). The only
disadvantage is that the analyzer has first to be calibrated with the
results of the standard chemical methods (10)(11)(12)(13);
therefore, the instrument is not more accurate than chemical methods.
Unfortunately, neither a gold standard nor calibrators exist for stool
analysis.
The Fenir 8820 Analyzer allows the determination of five major fecal
components in a single sample. As shown in Table 1
, the within-and
between-run CVs are <10%, except for starch, which shows very high
imprecision at low concentrations. These results are generally similar
to those reported in the literature
(3)(5)(15)(19)(20).
In our opinion, the imprecision for starch is unsatisfactory for
clinical use.
Homogenization can be avoided if repeated analyses on different portions of the same sample are performed. Picarelli et al. (20) found very similar CVs for water, fat, and nitrogen in homogenized and nonhomogenized stools, and Stein et al. (15) found similar CVs for carbohydrate. Nevertheless, we homogenized the feces by manual mixing. If a stool sample must be conserved, some authors (15)(21) recommend maintaining it at -20 °C until analysis. However, we analyzed specimens at the moment that we received them at the laboratory.
Benini et al. (14) reported that variation in stool matrix (e.g., liquid stools) could influence the results of fecal analysis. In our study, we did not focus on this possibility because the children were apparently healthy and did not have diarrhea. Because several intestinal, pancreatic, or biliary disorders can cause maldigestion-malabsorption syndromes, the importance of quantitative measurement of fecal nutrient output in the diagnosis of malabsorption-maldigestion syndromes has been recognized (1)(2). Some of these diseases are prevalent in children. Moreover, evaluation of adequate food intake and its absorption is of great importance for assessing the development of infants, especially during the first year of life. For this reason, the determination of reference intervals for these nutrients in feces is important.
The children were divided into four age groups, mainly according to
their different diets. Children from group 1 consumed fruits, cereal,
vegetables, and breast or formula milk. In group 2, children ate
fruits, cereal, meat, fish, vegetables, and formula milk. The diet of
children from group 3 was a combination between diets from groups 2 and
4. These children ingested less fruits and vegetables than group 2.
Children from group 4 consumed a free diet, generally the same as their
families and society. The significant differences found between these
groups supported the derivation of independent reference intervals for
each group (Tables 2
and 3
). In general terms, the excretion of all
nutrients (g/day) rises according to the age of the children, possibly
because each child ingests more nutrients as he or she grows older.
In our review of the literature, we found few comparable studies on this subject. Nevertheless, it is interesting to point out some specific aspects of our own study. The population was not gaussian if data were expressed as nutrient excretion (g/day), possibly explained by the introduction of fecal weight into the calculations. Fecal weights varied considerably in every group. Interestingly, Thorsgaard Pedersen et al. (22) found that the 3-day fat concentration (g/100 g) is as effective as fecal fat excretion (g/day), that fat concentration is more constant than fecal weight, and that 1-day fat concentration measurement is as effective as the 3-day measurement.
The lowest amount (g/day) of water was found in group 1 (Table 3
).
Constipation and hard stools are a major complication in formula-fed
children (23). Of the children in group 1, 88% were formula
fed. Nevertheless, we found a larger concentration of water than had
been reported by others (4)(24).
On the other hand, fat malabsorption in the first months of life is a
well-known phenomenon, which has been attributed to possible factors
such as reduced lipase activity (25) or the composition of
the feeding fat (26). We did not find steatorrhea (described
as fat >5 g/day) in group 1, although in this group, this nutrient is
the major one in percentage terms (Table 2
). On the contrary, a high
excretion output of fat was found in groups 3 and 4 (Table 3
). We
cannot compare our results with those in the literature, either because
others have studied an adult population or because the techniques used
are different from ours. Only a single publication (27) was
similar to ours. These authors found that formula-fed children had a
fecal fat lipid of 10.3 ± 3 g/100 g.
Protein intake is kept low in the first months of age to preserve the
kidney from future disorders. Therefore, the lowest quantity of protein
measured as nitrogen was found in group 1 (Table 3
). Likewise, children
have lower nitrogen values than adults because they metabolize proteins
better than adults.
Cereal is usually the first solid food given to young children. Children in group 1 were fed with cereal as a source of starch. Unfortunately, our results for starch were not satisfactory. The lower reference limits for starch were close to 0 g/100 g of feces, and the higher reference limit was close to the median in the four groups. We believe that the reference intervals obtained for the starch were wrong because of the instrument limitations. The Fenir 8820 cannot read >10 g of starch/100 g of feces. For this reason, we have not reported the results for starch determination in this paper.
The highest concentration of sugar was found in the stools of group 1
(Table 2
), but this group had the lowest total output (g/day; Table 3
).
Human and formula milk contain ~7% and 5.4–8.6% sugar,
respectively, and formula milk contains substantial quantities of
unabsorbable carbohydrate (28).
In summary, this new technology for measuring the major nutrients in stools is a major advance in the nutritional-digestive area. The method is simple to perform. Every laboratory should obtain its own reference intervals, especially when, as in this case, diet plays an important role.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The following articles in journals at HighWire Press have cited this article:
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  K. J Schulze, K. O O'Brien, E. L Germain-Lee, D. J Baer, A. Leonard, and B. J Rosenstein Efficiency of calcium absorption is not compromised in clinically stable prepubertal and pubertal girls with cystic fibrosis Am. J. Clinical Nutrition, July 1, 2003; 78(1): 110 - 116. [Abstract] [Full Text] [PDF]
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 J. Walkowiak, K.-H. Herzig, K. Strzykala, J. Przyslawski, and M. Krawczynski Fecal Elastase-1 Is Superior to Fecal Chymotrypsin in the Assessment of Pancreatic Involvement in Cystic Fibrosis Pediatrics, July 1, 2002; 110(1): e7 - 7. [Abstract] [Full Text] [PDF]
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