Public health surveillance use 85th centile as definition for overweight, and 95th centile for obesity (UK says “at risk of obesity”…). Clinical definitions (SACN/RCPCH 2012, NICE) however are different: (UK 1990, use special BMI chart)
- Obesity = BMI >98th centile for age (2 standard deviations, one tail)
- Overweight = >91st centile (1.3 SD)
Growth charts then label:
- Severe obesity = 99.6th centile (2.67 SD)
- Morbid obesity = 3.33 SD. High probability of co-morbidity, unlikely to improve by age 16.
- (some guidelines use Extreme = 4 SD)
Cut off for overweight/obesity high in babies, starts at 18/20 age 2, nadir of 17/19 at age 5, rising to 20/24 at 10 then usual 25/30 at age 18. Girls same as boys, slightly fatter after 10 yrs. Chart is in the SIGN guideline 115. [International data, BMJ 320:1242.]
Centile charts show centile spaces that are equivalent to 2/3 of a standard deviation. When you get to high centiles, you need something better than “above the 99.8th centile” so you use Z score, which is the number of standard deviations above the mean
Calculators available to calculate BMI and Z-scores eg Phsim.man.ac.uk/SDSCalculator
So secondary referral for:
- extreme, or
- ?secondary obesity, eg
- under 2 yrs with severe (>99.6th centile) obesity
- short for age
- co-morbidity eg strong FH type 2 DM, sleep apnoea, idiopathic intracranial hypertension, orthopaedic probs
- psychological comorbidity,
2nd care history –
- menstrual hx,
- sleep eg Chervin questionnaire (adds anything?)
- acanthosis nigricans (neck, flexures) – highly associated with insulin resistance
- buffalo hump. Striae and obesity as only signs of Cushings v rare. Striae in Cushings more intense red!?
- Mid-Parental Height – endocrinopathy unlikely if normal growth
- Waist circumference
- Goitre – hypothyroidism
- Peak flow
- Syndrome eg BWS
- Acne, Hirsutism – polycystic ovary syndrome
Little evidence for investigations, not routine.
- Fasting glucose, insulin, lipids
- FBC, U&Es, LFTs
- SHBG (marker of insulin resistance)
For more severe cases, consider:
- OGTT – 2hr glucose >11.1=diabetes, 7.8-11.1 = impaired glucose tolerance. Esp if S Asian, other signs/risks of insulin resistance.
- Sleep study
- Molecular genetics (EDTA) eg Prader Willi, Bardet-Biedl syndrome, Cohen syndrome, MOMO syndrome.
- Urinary cortisol/creatinine
- Low dose dexamethasone test (more sensitive than above but needs overnight admission) – cortisol should suppress below 100, else suggests Cushings
- CT head (if suspicion of raised intracranial hypertension
Homa-IR >4.5 for insulin resistance [Score = (Fasting insulin)*(Fasting glucose) / 405, measuring in mg/dl]. Transient increase in insulin resistance seen in puberty, independent of BMI.
Total choles:HDL 3.6 95th, 4.3 99th but no great paed data.
ALT>70 twice should proceed to USS to look for fatty liver, >100 urgent (for differential more than anything, although non alcoholic fatty liver disease can be progressive).
Delicate! Moral issue too – for example:
- uncertain benefits on physical health
- negative psychosocial consequences including uncertainty, fear, stigmatization
- aggravating inequalities
- disregarding the social and cultural value of eating
- infringement upon personal freedom regarding lifestyle choices and raising children
Addressing these issues may avoid resistance [Erasmus medical centre, Obes Rev. 2011 Sep;12(9):669-79. doi: 10.1111/j.1467-789X.2011.00880.x. Epub 2011 May 4]
- Initiate a conversation. Anticipate defensiveness
- Discuss “healthier weight” concept
- Positive, non-judgmental language
- Terms such as ‘obese’ are not generally well accepted by parents/carers
Opportunistic is good, but probably sensible to check that this is a good time, or at least create an invitation to start this conversation. And then, do more questioning and listening than advising.
The above section may already have brought up issues of low self-esteem and poor motivation. Building a therapeutic relationship, using motivational interviewing skills, is key then, especially where parents/children may have sensed discrimination and bias in the past.
General advice should include: (SIGN)
- Healthier eating, and decreased calorie intake
- At least 60 mins of moderately vigorous activity per day, pref habitual eg brisk walking! Given that evidence that moderate/high levels of cardiorespiratory fitness appear to attenuate or even eliminate the risks, just as important to emphasize fitness as weight loss?
- Max 2 hours screen time per day!
But as indicated above, probably more important to ask about the blocks, than to say “eat less, move more”.
OSCA 2012 Viner, arch dis child educ (paeds network)