FEATURE
A Two-Number System to
Report Body Mass Index
Rick Voakes, MD; and Andrew A. Bremer, MD, PhD
O
besity is associated with many
severe and potentially lifethreatening conditions, such as:
type 2 diabetes; atherosclerotic cardiovascular disease; metabolic syndrome
(insulin
resistance-hypertension-dyslipidemia); polycystic ovary syndrome;
and nonalcoholic fatty liver disease, to
name a few. Although obesity per se is
not the sole cause of these conditions,1
their association with excess weight is
useful because it alerts the busy clinician
that an overweight individual is at risk
for this group of illnesses.
In fact, obesity often precedes other
pathologic changes in these conditions
and, thus, could be thought of as the “fever” of metabolic dysfunction.
In order to utilize excess weight as
a tool for identifying individuals at risk
Rick Voakes, MD,
for metabolic dysfunction in clinical
practice, it would be helpful to quantify it in a manner that makes sense to
both the practitioner and the patient. The
body mass index (BMI), denoted as kg/
m2, is widely used as a simple screening method that requires only two easily
obtained measurements: the height (converted to meters [m] then squared [m2]);
and weight (converted to kilograms
[kg]). Practically, the BMI can be rapidly calculated with a computer or portable hand-held “BMI wheel” (using either metric or English units). Moreover,
it can be obtained in both the doctor’s
office as well as in schools2 and is useful
in correlating the level of obesity with
potential adverse outcomes.3 However,
is a private practitioner
in Bowling Green, KY, and also works with the
Healthy Weight Kids Coalition of Southern Kentucky. Andrew A. Bremer, MD, PhD, is Assistant
Professor, Department of Pediatrics, Division of
Medicine.
Address correspondence to: Rick Voakes, MD,
Healthy Weight Kids Coalition of Southern Kentucky, PO Box 54, Bowling Green, KY 42102; fax:
270-782-7773; email: [email protected].
Disclosure: Dr. Voakes has no relevant financial relationships to disclose. Dr. Bremer has received payment from Pfizer for a lecture on the
use of growth hormone in cases of growth hormone deficiency.
doi: 10.3928/00904481-20120625-11
PEDIATRIC ANNALS 41:7 | JULY 2012
© iStockphoto.com
Endocrinology, Vanderbilt University School of
Healio.com/Pediatrics | 289
FEATURE
the problem with BMI in children is that
normative values are sex- and age-dependent, precluding the use of absolute
cut-off numbers for overweight and obesity, such as those that are used in adults
(25 kg/m2 and 30 kg/m2, respectively).
In order to deal with this obstacle, the
concept of “percentile for age” is used
almost universally in the pediatric setting. This works well for research purposes, but it has many limitations in the
clinical setting.
First, the statistical concept of “percentiles” is difficult for pediatric patients
and their families to comprehend. After
all, it does not make sense to many individuals how 32% of children and adolescents in the Unites States can currently
be at or above the 85th percentile of the
currently used growth charts (the 2000
sex- and age-specific Centers for Disease
Control and Prevention [CDC] growth
charts).4 Second, parents frequently do
not identify their own children as overweight or obese,5 regardless of what
“percentile” their child is in. Third, a
large percentage of pediatricians do not
use electronic medical records and, thus,
do not get an instant read-out of each patient’s BMI percentile,6 making it difficult during a busy clinic visit to quickly
tell a family the “normal” BMI for their
child’s age.
The intent of the percentile system
was to establish norms for BMI at various ages. However, to circumvent the
widespread misunderstanding of what
“percentiles” really mean to the lay public, we propose that the concept of “percentiles” be dropped in clinical practice
in place of a system that is readily understood by practitioner and patient and/or
family alike. But how can new “norms”
be established that approximate the percentile norms that are in common use?
As it turns out, the currently used
2000 CDC growth chart curves for the
85th BMI-for-age percentiles (the cut-off
point for overweight) for both boys and
girls closely follow a fairly linear pat290 | Healio.com/Pediatrics
tern between the ages of 7 and 15 years,
which corresponds to the patient’s age
plus 10 (age + 10). For practical purposes, the adult “85th percentile” norm of 25
kg/m2 can be used to denote overweight
in adolescents older than 15 years of age
(15-year-old + 10 = 25); before 7 years
of age, the value of 17 kg/m2 (7-year-old
+ 10 = 17) can be used. Although there
are minor deviations from the traditional
85th percentile for BMI in
children aged 7 to 15 years
closely follows a linear curve
which corresponds to
“age + 10.”
CDC-defined 85th BMI-for-age percentiles using the “age + 10” calculation for
those patients aged 7 to 15 years, they
are neither adverse nor detract from the
clinical utility of quickly approximating (without access to a BMI percentile
chart) the “overweight” BMI cut-off for
a patient in the busy clinical setting.
PROPOSAL
To avoid the shortcomings in clinical practice with using the traditional
“percentile” system, we propose a new
method to report BMI – a two-number
notation in which the raw BMI score is
compared with the upper limit of normal
for age (corresponding to approximately
the 85th BMI-for-age percentile). Using
this system, the BMI would be written
similar to a blood pressure measurement,
with the raw BMI score written first (the
top number) and the upper limit of normal written second (the bottom number).
For example, a 9-year-old child (boy or
girl) with a raw BMI score of 21 kg/m2
would have a BMI of 21/19 (pronounced
“twenty-one over nineteen”), with the
bottom value of 19 derived using the
“age + 10” method of estimating the
85th BMI-for-age percentile (described
above). Both the physician and parent
(and child!) would easily be able to tell
that 21 is a bit above the upper-normal
BMI value of 19 and, thus, understand
that the child is overweight. This method
is quick, easy, and effective.
Are there children with a normal
BMI who are at risk for or who already
have metabolic dysfunction? Absolutely,
and this is a drawback of using BMI as
the sole screening tool for metabolic abnormalities.7 Primary care physicians,
thus, need to examine other factors associated with metabolic dysfunction (such
as family history, a sedentary lifestyle,
and a diet that includes sugar-sweetened
beverages).8 Are there children with
an abnormal BMI (above the uppernormal for age) who do not have metabolic dysfunction? Yes, and although the
prevalence of metabolic abnormalities is
higher among obese children than normal-weight children,9 not every obese
child has metabolic syndrome or one
of its associated conditions. However,
given that weight gain during childhood
and adolescence influences a child’s
risk of becoming overweight or obese
later in life,10 quickly identifying a child
as overweight in the context of a busy
clinical practice using the two-number
system — and effectively conveying that
information to the patient and/or family in an easily understood manner — is
paramount. First, it would provide easyto-understand objective data supporting
the provider’s recommendation for a
healthier diet and lifestyle (a treatment
with no potential adverse effects); second, it may potentially increase patient/
family adherence to weight management
strategies.
CONCLUSION
The BMI is easily calculated — in
both the inpatient and outpatient setting
— using a patient’s height and weight.
In children, the norms are constantly
changing with age, but the upper limit of
PEDIATRIC ANNALS 41:7 | JULY 2012
FEATURE
normal follows a fairly linear pattern between the ages of 7 and 15 years in both
sexes, which approximately equals the
child’s age + 10. Younger than the age
of 7 years, the upper-normal BMI is approximately 17 kg/m2; older than the age
of 15 years, the upper-normal BMI remains at the adult level of 25 kg/m2. We
propose a simple way to report BMI in
pediatric patients that includes both the
raw BMI number as well as an approximation for the upper norm for age, giving the pediatrician and the patient and/
or family a better perspective on what the
BMI should be for any given age. Thus,
we suggest that the BMI — at least in
the clinical setting — be reported as two
numbers, similar to a blood pressure
reading, with the raw calculation as the
top number and the approximated upper
norm for age as the bottom number.
REFERENCES
1.Sheehan MT, Jensen MD. Metabolic complications of obesity. Pathophysiologic considerations. Med Clin North Am. 2000;84(2):363385.
2.Nihiser AJ, Lee SM, Wechsler H, et al.
BMI measurement in schools. Pediatrics.
2009;124(Suppl 1):S89-S97.
3.Kirk S, Zeller M, Claytor R, Santangelo
M, Khoury PR, Daniels SR. The relationship of health outcomes to improvement in
BMI in children and adolescents. Obes Res.
2005;13(5):876-882.
4.Ogden CL, Carroll MD, Flegal KM. High
body mass index for age among US children and adolescents, 2003-2006. JAMA.
2008;299(20):2401-2405.
5. Eckstein KC, Mikhail LM, Ariza AJ, Thomson
JS, Millard SC, Binns HJ. Parents’ perceptions
of their child’s weight and health. Pediatrics.
2006;117(3):681-690.
6.DesRoches CM, Campbell EG, Rao SR, et al.
Electronic health records in ambulatory care-a national survey of physicians. N Engl J
Med. 2008;359(1):50-60.
7. St-Onge MP, Janssen I, Heymsfield SB. Metabolic syndrome in normal-weight Americans:
new definition of the metabolically obese,
normal-weight individual. Diabetes Care.
2004;27(9):2222-2228.
8. Bremer AA, Auinger P, Byrd RS. Relationship
between insulin resistance-associated metabolic parameters and anthropometric measurements with sugar-sweetened beverage intake
and physical activity levels in US adolescents:
findings from the 1999-2004 National Health
and Nutrition Examination Survey. Arch Pediatr Adolesc Med. 2009;163(4):328-335.
9.Weiss R, Dziura J, Burgert TS, et al. Obesity
and the metabolic syndrome in children and adolescents. N Engl J Med. 2004;350(23):23622374.
10.Dietz WH. Health consequences of obesity in
youth: childhood predictors of adult disease.
Pediatrics. 1998;101(3 Pt 2):518-525.
CME
ONLINE
Examining the Psychosocial Ramifications of
Type 1 Diabetes in Children
Through compelling patient interviews and interactive cases, this activity will educate clinicians on
various strategies that will help adolescents with T1DM and their families cope with the disease,
improve treatment adherence, and identify/address negative psychosocial issues.
Learn how to ensure effective
interventions for handling
glycemic control and
psychosocial issues
COURSE CHAIRS
Thomas W. Donner, MD
Baltimore, Maryland
David H. Madoff, MD, PhD
Baltimore, Maryland
FACULTY
Alan Delamater, PhD
Miami, Florida
Gun Forsander, MD, PhD
LEARNING OBJECTIVES
After participating in this activity, the participant will demonstrate the ability to:
• ASSESS psychosocial issues associated with T1DM in children and adolescents.
• EVALUATE effective interventions for understanding and managing psychosocial issues associated
with T1DM in children and adolescents.
• EXPLAIN effective management strategies to parents, children, and other caretakers when children
may be away from the home or in transition to adulthood.
• INTEGRATE multi-professional team members into their practice when caring for children and
adolescents with T1DM.
Participate in this activity at Healio.com/Pediatrics/Education-Lab
Gothenburg, Sweden
Linda Siminerio, RN, PhD, CDE
Pittsburgh, Pennsylvania
This continuing medical education activity is presented by the Johns Hopkins University School of Medicine.
12-0971
The Johns Hopkins University School of Medicine is accredited by the Accreditation Council for Continuing Medical
Education to provide continuing medical education for physicians.
This activity is supported by an educational grant from Lilly USA, LLC.
The Johns Hopkins University School of Medicine designates this enduring material for a maximum of 1.5 AMA PRA
Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in
the activity.
This enduring material is approved for 2 years from the date of original release, 12/31/2011 to 12/31/2013.