Cohort Profile: The KPSC Children's Health Study, a population-based study of 920 000 children and adolescents in southern California
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Published by Oxford University Press on behalf of the International Epidemiological Association International Journal of Epidemiology 2012;41:627–633
ß The Author 2011; all rights reserved. Advance Access publication 20 January 2011 doi:10.1093/ije/dyq252
COHORT PROFILE
Cohort Profile: The KPSC Children’s Health
Study, a population-based study of 920 000
children and adolescents in southern California
Corinna Koebnick,1* Karen J Coleman,1 Mary Helen Black,1 Ning Smith,1 Jack K Der-Sarkissian,2
Steven J Jacobsen1 and Amy H Porter3
1
Department of Research and Evaluation, Kaiser Permanente Southern California, Pasadena, USA, 2Los Angeles Medical Center,
Southern California Permanente Medical Group, Los Angeles, USA and 3Baldwin Park Medical Center, Southern California
Permanente Medical Group, Baldwin Park, USA
*Corresponding author. Department of Research and Evaluation, Kaiser Permanente Southern California, 100 Los Robles,
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2nd Floor, Pasadena, CA 91101, USA. E-mail: corinna.koebnick@kp.org
Accepted 1 December 2010
How did the study come about? offering a unique opportunity to fill current know-
ledge gaps regarding the disease burden associated
Paediatric obesity rates have reached epidemic propor- with childhood obesity. These guidelines include regu-
tions in the USA, affecting 16.9% of children and ado- lar screening of blood lipids, liver enzymes and mark-
lescents.1 Although recent nationwide trend analyses ers of glucose metabolism recommended for children
suggest that paediatric obesity rates are no longer at or above the 95th percentile of BMI-for-age accord-
increasing, data also show a shift towards extreme ing to the 2000 sex-specific Centers for Disease
obesity.1 Increasing concerns focus on the effects of Control and Prevention (CDC) growth charts2 and
obesity on morbidity and health-related quality of life for children at or above the 85th percentile when add-
issues, particularly in cases of paediatric onset of itional risk factors such as a family history of diabetes
obesity. However, the economic burden and long-term or dyslipidaemia are recorded in the electronic health
health consequences of extreme childhood obesity are record. Weight and height are measured at almost
largely unknown and ill-defined because there have every medical encounter in KPSC. Thus, there is an
been no large prospective epidemiological studies that almost complete coverage of paediatric KPSC mem-
included enough extremely obese children to deliver bers who had medical encounters since 2007 regard-
stable estimates of the health consequences. ing body mass index (BMI).
To address current gaps in the knowledge about
the health consequences of extreme childhood obes-
ity, we created a contemporary cohort study of chil-
dren and adolescents 2–19 years of age in southern What does it cover?
California who are actively enrolled in a large, pre- The goal of the KPSC Children’s Health Study is to
paid, integrated managed healthcare system. The estimate the association between the severity of obes-
Kaiser Permanente Southern California (KPSC) ity and adverse health conditions in children and
Children’s Health Study is an ongoing cohort study adolescents 2–19 years of age. The adverse health con-
that currently includes 4920 000 children and adoles- ditions of childhood obesity include those conditions
cents and continues to enrol new patients joining that are related to the metabolic syndrome and poten-
the health plan. The study is currently supported by tial consequences of the chronic inflammation under-
a grant from the National Institute of Diabetes and lying obesity: impaired glucose tolerance,
Digestive and Kidney Disorders (R21DK085395; dyslipidemia, elevated blood pressure and hepatic dis-
Principal Investigator: Koebnick) and by Kaiser ease. Ancillary studies include outcomes such as psor-
Permanente Direct Community Benefit Funds. iasis, rheumatic diseases, gallstones and idiopathic
Since 2007, new screening guidelines for paediatric intracranial hypertension. The study will also assess
weight management have been implemented at KPSC the potential modification of the association between
627628 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY the severity of obesity and adverse health conditions Permanente Medical Group, a partnership of 46000 by demographic factors such as sex, race/ethnicity and physicians who represent the entire range of medical age. Because prospective data are being collected, specialists who provide the vast majority of care current studies primarily are cross-sectional studies received by KPSC members. Members and their from the cohort inception. families enrol through their employer, the employer Besides health consequences of extreme childhood of a family member, an individual prepaid plan or a obesity, the aim of the KPSC Children’s Health Study state or federal programme such as Medi-Cal, is to provide insight into the concept of ‘extreme obesity’ CALPERS or Medicare. Children receive medical care in children, which currently lacks a standard definition. mainly from KPSC paediatricians, and also may be The 2000 CDC growth charts lack the precision neces- seen by family practitioners, specialists or other sary to calculate percentiles
KPSC CHILDREN’S HEALTH STUDY 629
Table 1 Demographic characteristics of KPSC members virtually all aspects of care delivered is captured and
2–19 years of age who are currently included or excluded extracted for research purposes. All administrative
from the KPSC Children’s Health Study and clinical data are linked through a unique medical
record number and include membership information
KPSC Currently and benefits, medical encounters, disease codes,
Children’s excluded
Health KPSC health claims, laboratory test results, pharmaceuticals
Variable Study Cohort members dispensed, treatments administered and procedures
n 920 034 375 937 performed in pathology as well as pathology and radi-
Sex
ology results. Information for the KPSC Children’s
Health Study is updated on an annual basis.
Male (%) 49.9 53.3
Age group (%)
2–5 years 25.2 14.8
6–11 years 28.7 27.7
What has been measured?
12–19 years 46.1 57.4 Outcome ascertainment
Race/ethnicity (%) Disease outcomes are extracted from electronic health
Non-Hispanic White 21.1 21.9
records using International Classification of Diseases
(ICD-9) codes and KPSC internal diagnosis codes. The
Hispanic 51.0 43.5
records per medical encounter contain up to 45 diagnos-
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Black 7.5 4.9 tic codes and up to 45 procedure codes. The validity
Asian or Pacific Islander 6.8 5.2 of diagnosis codes is relatively high in this integrated
American Indian/Alaskan Native 0.1 0.1 healthcare system. Due to referral to specialists and
Multiple races 0.5 0.2 removal of wrong diagnosis codes, the validity for
most diagnosis codes is well above 90%. Diagnosis val-
Others 1.2 0.7
idations have been performed in many areas such as
Unknown race/ethnicity 11.8 23.6 psoriasis and psoriatic arthritis,5 gestational diabetes,6,7
Service area (%) gastroesophageal reflux disease8 and cardiovascular
Los Angeles Metropolitan Area 48.0 58.9 disease.9 Special diagnosis validation in this paediatric
Orange County 11.8 5.8 population is ongoing.
Inland Empire 24.1 23.8 Cardiovascular risk factors such as blood pressure,
blood lipids and glucose levels are extracted from the
Kern County 3.5 0.0
vital signs and the laboratory results of the electronic
San Diego 12.7 7.4 health record.
Neighborhood education (%)
Less than high school 28.5 30.2 Race and ethnicity
High school graduate 21.5 21.9 Race and ethnicity information was obtained from
Some college or associate degree 30.3 29.8 birth certificate information for 27.7% of the cohort
Bachelor degree or higher 19.7 18.1 members. If no birth certificate was available, race
Neighbourhood income (%) and ethnicity information was obtained from health630 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
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Figure 2 Source of race and ethnicity information in the KPSC Children’s Health Study
was 498%. Asian/Pacific Islander race was assigned divided by the square of the height (metres). For each
when the probability cut-off for surname was 440% year (2007–09), the median BMI-for-age of all en-
for Asian/Pacific Islander race. Hispanic ethnicity was counters for a patient from the most recent available
assigned when the probability cut-off for surname year was used for these analyses. Based on a valid-
was 450% for Hispanic ethnicity. For Blacks and ation study including 15 000 patients with 45 980
non-Hispanic Whites, members’ addresses were geo- medical encounters, the estimated error rate in body
coded to the US Census Block level. Race and ethni- weight and height data wasKPSC CHILDREN’S HEALTH STUDY 631
Table 2 Percentage of active KPSC members on 15 January
2005, 0–24 years of age and the percentage retained in the
What are the main strengths and
KP plan between 2005 and 2010 weaknesses?
Retention of active members (%) in years The KPSC Children’s Health Study is unique with re-
spect to the population size and the broad informa-
Age (years) 2005 2006 2007 2008 2009 2010 tion provided by an integrated healthcare system with
0–2 100 89.9 82.6 76.8 71.8 66.5 access to laboratory results and medical diagnoses.
3–6 100 91.0 84.4 79.1 74.1 68.8 The study sample currently includes 89.2% of eligible
7–12 100 92.0 86.0 80.9 76.3 71.1 KPSC members. One particular advantage of this
setting is that all clinical data represent routine
13–17 100 92.5 83.1 73.6 63.8 51.5
healthcare delivered to KPSC patients by KPSC pro-
18–24 100 80.4 67.5 56.1 45.6 35.8 viders; these data are therefore indicative of typical
healthcare decisions. All subjects have relatively con-
sistent health insurance benefits, and clinicians are
influenced by a consistent incentive system and cen-
are older, more likely to be male and of unknown race tralized efforts to standardize practice. Thus, there are
and ethnicity. minimal effects on utilization and outcomes from
The 5-year retention rate for children and adolescents insurance coverage that may confound outcomes in
from recent years at KPSC is a function of health
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other settings. The KPSC Children’s Health Study rep-
plan membership and varies by age group with the resents 12.3% of the population in the counties of
highest 5-year retention in 7- to 12-year-old children southern California served by KPSC, includes a large
and the lowest 5-year retention in adolescents and number of children from low-income groups and is
young adults (Table 2). Due to recent policy changes roughly comparable regarding most sociodemographic
that grant longer insurance coverage for young adults factors.
under their parent’s health insurance, we expect these The study is also unique in its inclusion of a large
retention rates to increase over the next few years. number of severely obese children, which will enable
Although long-term follow up is dependent on contin- us to conduct stratified analyses for important poten-
ued membership, some events such as death and cancer tial effect modifiers. Additionally, the study setting
can be traced through probabilistic linkage with allows for collection of data on laboratory markers
the California state and national death files and and diagnoses made by physicians, which are not
cancer registry files. If younger participants lose health available in other cohort studies, such as National
coverage due to loss of employment of their parents, Health and Nutrition Examination Survey.
they may continue health care under a state or federal A potential strength and limitation of the proposed
programme such as Medi-Cal, CALPERS or Medicare. study is the follow up through passive surveillance
Most children included in the study have been which offers unique opportunities to follow an ex-
members for many years. The average length of mem- tremely large population. However, it also implies
bership before study enrolment (mean SD) is some restrictions arising from real life as opposed to
2.6 1.6 years for children 2–5 years of age, research settings. These restrictions include a poten-
5.8 3.7 years for children 6–11 years of age and tial variation in the proportion of children who are
9.3 6.1 years for children 12–19 years of age. screened for obesity-related conditions within KPSC.
Thirty per cent of children in the cohort were born Physician’s screening behaviour may vary across med-
in KPSC hospitals and have been members since birth ical centres. Because most of these conditions are
(Table 1). silent conditions without symptoms, children may
not seek a doctor’s attention and may not be tested.
The true prevalence of some conditions may not be
estimable since data were not generated by a compre-
What are the key findings and hensive screening of the entire KPSC population of
the targeted age range. However, the increasing
publications number of screening tests, such as glucose and chol-
Previous results from the study have shown that 7.3% esterol, performed each year suggests a high aware-
of boys and 5.5% of girls in southern California can be ness of KPSC physicians for populations at risk for
classified as extremely obese.4 The prevalence of ex- obesity-related conditions. Computer-assisted aids im-
treme obesity peaked at 10 years of age in boys and at plemented in the medical record system make com-
12 years of age in girls, with a bimodal distribution in pliance with the screening recommendations feasible
girls (second peak at 18 years, P for sex age inter- by BMI-triggered ‘best practice’ alerts that make the
action ¼ 0.036). The prevalence of extreme obesity physicians aware of the condition (i.e. obesity) and
varied among ethnic/racial and age groups with the recommend screening for risk factors. Laboratory
highest prevalence in Hispanic boys (up to 11.2%) and orders can then be placed by simply clicking on the
Black girls (up to 11.9%).4 alert flag.632 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
Another potential limitation of the study is the re- principal investigator of the study, Dr Corinna
stricted availability of cardiovascular screening results Koebnick, can be contacted for more information.
in children who are normal weight and healthy.
Screening for abnormalities in fasting glucose, blood
lipids and liver enzymes is usually only performed in
children who are overweight unless other conditions Funding
require surveillance of these factors. Therefore, silent The KPSC Children’s Health study is supported by the
conditions such as liver disease may only be diag- National Institute of Diabetes and Digestive and
nosed in children who were screened (¼ obese chil- Kidney Disorders at the National Institutes of Health
dren) but not in others (¼ normal-weight children), (R21DK085395) and by Kaiser Permanente Direct
which would lead to an overestimation of the associ- Community Benefit Funds.
ation between obesity and adverse health outcome. It
is noteworthy, however, that some vital signs such as
blood pressure are measured at every visit regardless
of body weight and will be available in all children. Acknowledgements
Using overweight children who were screened as ref- We thank Britta Amundsen, Julie Stern, Margaret
erence as well as multiple imputation methods can Chi, Alexander Carruthers, Theresa Im and the
partially compensate for these restrictions. KPSC Research and Evaluation research support
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In addition, utilization may vary due to slight vari- team for their diligent work and incredible validation
ations in the health plans including variations in and data quality efforts. We are also especially grate-
co-payments for office visits or medical procedures ful to all our members who made this study possible.
such as laboratory tests or imaging. High co-payments
may negatively affect the likelihood of undergoing Conflict of interest: None declared.
certain preventive screening procedures, and conse-
quently, the likelihood of being diagnosed with
some health conditions. However, highly deductible
plans with varying benefits and high medication
References
1
co-pays were not offered comprehensively at KPSC Ogden CL, Carroll MD, Curtin LR, Lamb MM, Flegal KM.
until 2006, and mostly do not affect health care for Prevalence of high body mass index in US children and
families with children. On the other hand, the KPSC adolescents, 2007–2008. JAMA 2010;303:242–49.
2
population also includes a large number of children Cole TJ, Bellizzi MC, Flegal KM, Dietz WH. Establishing a
receiving full or additional coverage through Medi-Cal standard definition for child overweight and obesity
worldwide: international survey. BMJ 2000;320:1240–43.
and other subsidized plans. Therefore, we do not 3
Flegal KM, Wei R, Ogden CL, Freedman DS, Johnson CL,
expect this to have an impact on our findings.
Curtin LR. Characterizing extreme values of body mass
Race and ethnicity were not systematically collected index for age by using the 2000 Centers for Disease
on every member of KPSC. Multiple sources were Control and Prevention growth charts. Am J Clin Nutr
used to supplement existing race/ethnicity data, 2009;90:1314–20.
including imputation of race and ethnicity informa- 4
Koebnick C, Smith N, Coleman KJ et al. Prevalence of
tion for 19.9% of the current cohort, which was pri- extreme obesity in a multiethnic cohort of children and
marily based on surname probabilities. However, we adolescents. J Pediatr 2010;157:26–31 e2.
expect the potential bias that may be introduced by 5
Wu JJ, Porter AH, Black MH, Smith N, Jacobsen SJ,
the imputation procedure to be minimal and to out- Koebnick C. Low prevalence of psoriasis among children
weigh the potential bias in classifying these members and adolescents in a large multiethnic cohort in southern
as an unknown race. California. J Am Assoc Dermatol 2010. in press.
6
Lawrence JM, Black MH, Hsu JW, Chen W, Sacks DA.
Prevalence and timing of postpartum glucose testing and
sustained glucose dysregulation after gestational diabetes
mellitus. Diabetes Care 2010;33:569–76.
Can I get access to the data? 7
Lawrence JM, Contreras R, Chen W, Sacks DA. Trends in
Where can I find out more? the prevalence of preexisting diabetes and gestational
diabetes mellitus among a racially/ethnically diverse
Information on the KPSC Children’s Health Study is
population of pregnant women, 1999–2005. Diabetes Care
available at http://xnet.kp.org/research/. Because the 2008;31:899–904.
information contained in electronic health records is 8
Koebnick C, Getahun D, Porter AH, DerSarkissian JK,
protected and confidential, it can be extremely diffi- Jacobsen SJ. Extreme childhood obesity is associated
cult to exchange individual level information. with increased risk for gastroesophageal reflux disease.
Therefore, individual level information from several Int J Pediatr Obes 2011;6:e257–63.
sources is usually managed, analysed and aggregated 9
Karter AJ, Ferrara A, Liu JY, Moffet HH, Ackerson LM,
at the KPSC data centre in projects with external col- Selby JV. Ethnic disparities in diabetic complications in
laborators. Active collaborations are welcome and the an insured population. JAMA 2002;287:2519–27.KPSC CHILDREN’S HEALTH STUDY 633
10 13
Smith N, Iyer R, Langer-Gould A et al. Health plan Flegal KM, Wei R, Ogden CL, Freedman DS, Johnson CL,
administrative records versus birth certificate records: Curtin LR. Characterizing extreme values of body mass
quality of race and ethnicity information in children. index for age by using the 2000 Centers for Disease
BMC Health Serv Res 2010;10:316. Control and Prevention growth charts. Am J Clin Nutr
11
Smith N, Coleman KJ, Lawrence JM et al. Body weight 2009;90:1314–20.
14
and height data in electronic medical records of children. Kuczmarski RJ, Ogden CL, Guo SS et al. 2000
Int J Pediatr Obes 2010;5:237–42. CDC Growth Charts for the United States: methods and
12
World Health Organization. Technical Report Series 894. development. Vital Health Stat 2002;11:1–190.
Obesity: Preventing and Managing the Global Epidemic. Geneva:
World Health Organization, 2000. ISBN 92-4-120894-5.
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