Comparison of total body chlorine, potassium, and water measurements in children with cystic fibrosis123

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ABSTRACT

Background:

Symptoms of cystic fibrosis (CF) may limit the utility of total body chlorine (TBCl) and total body potassium (TBK) measurements for assessing body fluid compartments of children.

Objective:

This study assessed relations among independent measurements of TBCl, TBK, and total body water (TBW) in children with CF.

Design:

We compared cross-sectional measurements of TBCl by in vivo neutron activation analysis, TBK by whole-body counting of 40K, TBW by D2O dilution [TBW(D2O)], and TBW from TBCl and TBK [TBW(Cl + K)] in 19 prepubertal children (13 boys) aged 7.6–12.5 y who had mild symptoms of CF. Body-composition measurements were compared with data from previous studies of healthy children.

Results:

Subjects with CF had deficits in TBCl, TBK, TBW, and body weight compared with control reference data (P < 0.05). The ratios (TBCl + TBK)/TBW and TBCl/TBK were not significantly different from control reference values, and plasma chlorine and potassium concentrations were within control reference ranges. The sum of TBCl and TBK correlated with TBW(D2O) (r2 = 0.79, P < 0.001), and TBW(Cl + K) correlated with TBW(D2O) (r2 = 0.78, P < 0.001). TBW(Cl + K) was similar to TBW(D2O) ( ± SEM: 19.0 ± 0.5 compared with 19.4 ± 0.5 L; NS).

Conclusions:

Prepubertal children with mild symptoms of CF can develop deficits in TBCl, TBK, and TBW that reflect chronic energy malnutrition. Mild symptoms of CF do not appear to affect normal relations among TBCl, TBK, and TBW. Measurements of TBCl and TBK may be used to assess body fluid compartments in these patients.

KEY WORDS

Body composition
total body chlorine
total body potassium
total body water
extracellular water
intracellular water
cystic fibrosis
prepubertal children

Cited by (0)

1

From the Department of Medicine, Monash University; the Department of Medical Physics and the Body Composition Laboratory, Monash Medical Centre; the Department of Gastroenterology, Royal Children’s Hospital; and the Department of Child Psychiatry, Austin Hospital, Melbourne.

2

DJ Borovnicar was funded by a Monash University Departmental Scholarship.

3

Address reprint requests to DB Stroud, Medical Physics, Monash Medical Centre, 246 Clayton Road, Clayton, VIC 3168, Melbourne, Australia. E-mail: [email protected].