Use of the Tanita TBF-300M body composition analyser in children with cystic fibrosis and healthy controls: a validation study using air displacement plethysmography

Cystic fibrosis (CF) is an inherited chronic illness characterised by exocrine
pancreatic failure and chronic respiratory infections. Malnutrition is a common
but largely preventable complication in children and adolescents with CF.
Nutritional care is considered an essential component of cystic fibrosis (CF)
management. Anthropometric measurements are routinely performed to assess
growth and nutritional status.

In addition to body weight and height measurements, body fat is estimated in
most CF patients, often from the measurement of skinfold thickness which can be
performed at low cost and is painless. However, its reproducibility is
dependent on the technician and validity depends on the amount of body fat.
Another non-invasive technique for the assessment of body composition that is
rapidly gaining popularity in the clinical setting is the Tanita leg-to-leg
bioimpedance analyser (BIA). The Tanita is portable, easy to use for patients
and technicians, and relatively inexpensive. The built-in BIA provides a
measurement of resistance (in Ohm) and estimates of total body water and body
fat. In healthy non-obese children, the Tanita proved to be reproducible and
valid when compared to DEXA (1). Although Tanita readings are useful in adult
CF patients (2) no validation studies with Tanita in CF patients have yet be
published.

Our plan is to validate the Tanita-300M for children aged 7-18 years .
Hydrostatic weighing would be the gold standard for the measurement of body
volume, body density and - as a derivative - body fat, but this is not feasible
in patients who have difficulties to breathe. A novel gold standard is air
displacement plethysmography, which can be measured non-invasively using the
Bodpod® device. In a recent study in 23 healthy children from Wageningen, the
Bodpod® had excellent accuracy and repeatability compared to hydrostatic
weighing (3). Thus, air displacement plethysmography will be used a reference
method.

To check whether air displacement plethysmography is a valid reference method
in CF children, we will also perform the two methods in healthy controls.

To assess whether the Tanita body composition analyser - a simple non-invasive
device to estimate body composition - can be used to estimate body fat% in
children and adolescents with cystic fibrosis in cross-sectional and
longitudinal studies.

All children will be measured with the Tanita and the reference method,
Bodpod®, at two time points with 4 months in between:

month controls (WU) CF (UMCU)
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Nov 2007 measurement 1
Jan 2007 measurement 1
March 2007 measurement 2
May 2007 measurement 2


The data collected during the first and second measurements (1 and 2) will be
used to compare body fat% measured by Bodpod® and Tanita using the Bland-Altman
analysis. This will be done for control children and CF patients separately.

The repeated measurements after 4 months will be used to assess changes (2 - 1)
in body fat% using the two methods.

The study will be observational; no intervention other than standard care will
be provided. Changes in food intake or physical exercise are allowed because
they do not interfere with our study.

The bioimpedance measurement with Tanita is safe, noninvasive, rapid (ca 30 s),
and familiar because it resembles standing on a normal bathroom scale.
The Bodpod® measurement is safe, but not suitable for claustrophobic persons.
All children will be made familiar and at ease with the measurements; no
pressure will be put on them to take part.
All participants will receive a report with their body weight, height, and body
fat%. The healthy controls - who voluntarily take part - will receive a small
fee or gift.