Obesity Initial Assessment

During a physical examination, it is important to measure the patient’s blood pressure in both arms to screen for hypertension, and to check for any evidence of thyroid disease, Cushing’s syndrome, hypogonadism, dysmorphism, and signs of insulin resistance (eg acanthosis nigricans).  

Assess the patient’s mental status (eg patient’s self-image, general mental health, stress factors, eating disorder, presence of depression and other mood disorders, substance abuse) and psychosocial barriers. A psychiatric referral is considered if the Patient Health Questionnare-9 score is ≥10 when screening for depression.  

Anthropometry  

Body Mass Index  

Body mass index (BMI) measures the weight relative to height. It indicates total body fat content and helps predict future health status as raised BMI increases cardiovascular events or deaths, total mortality, diabetes mellitus, sleep disorder, OA, and certain cancers (eg endometrial, breast, colon, kidney, esophagus).  

It is done annually for screening and as needed for management and is calculated by the formula: BMI = weight (kg)/height (m)². Asian countries have lower BMI cut-off points for overweight and obesity than the World Health Organization (WHO) BMI values.  

The calculation is for all age groups and BMI percentile for age is used in children <18 years old to determine the healthy weight status. High-risk fat accumulation is noted in adults of European descent with BMI ≥25 kg/m² and a waist-to-height ratio of >0.5. If BMI and physical exam findings are unclear, performing a dual-energy X-ray absorptiometry or bioelectric impedance to determine body composition and adiposity (percentage body fat and body fat distribution) is considered.

Waist Circumference and Waist-to-Hip Ratio (WHR)  

Waist circumference and the waist-to-hip ratio (WHR) are useful measures of intra-abdominal fat content before and during weight loss treatment. Waist circumference is measured at the approximate midpoint between the superior iliac crest and the lower margin of the last rib. The WHR is the maximum circumference (in cm) around the pubic symphysis anteriorly and the buttocks posteriorly. It is calculated by the formula WHR = waist circumference/hip circumference (measured around the pelvis at the point of maximal buttock protrusion).  

They are considered the measurements of choice for classifying central (waist circumference of ≥90 cm for Asian males and ≥80 cm for Asian females) obesity and clinical risk. They are useful for individuals with normal BMI or pre-obesity BMI. Waist circumference and WHR are measured annually for screening. An increased waist circumference is associated with an increased risk for type 2 diabetes mellitus, dyslipidemia, hypertension, MAFLD, and cardiovascular disease in patients who may not be considered obese by conventional BMI criteria.

ADULT CLASSIFICATION OF WEIGHT BY BODY MASS INDEX
WHO Classification	WHO BMI Cut-off Points (kg/m2)	Risk of Comorbidities	Asian BMI Cut-off Points (kg/m2)
Underweight	<18.5	Low but increased risk of other clinical problems	<18.5
Normal	18.5-24.9	Average	18.5-22.9
Overweight/Pre-obese	25.0-29.9	Increased	23.0-24.9
Obese Class I	30.0-34.9	High	25.0-29.9
Obese Class II	35.0-39.9	Very high	30.0-34.9
Obese Class III	≥40.0	Extremely high	≥35.0
Race High-Risk Waist Circumference (cm) High-Risk Waist-to-Hip Ratio Men Women Men Women Asians ≥90 ≥80 ≥1.0 ≥0.85 Caucasians ≥102 ≥88 ≥1.0 ≥0.85

A diagnosis of obesity can also be made in adults of European descent with a BMI of ≥25 kg/m2, a waist-to-height ratio >0.5, and the presence of any physiological, medical or functional impairments or complications. The presence of obesity warrants assessment for obesity-related comorbidities which should be graded according to severity if present. The treatment approach and goals are tailored according to the presence of obesity-related comorbidities and their severity. The presence of any obesity-related comorbidities also warrants assessment for obesity and its severity if not the presenting condition or the condition consulted for. 

Severity of Obesity  

Stage severity of obesity based on complication-specific criteria. 

OBESITY COMPLICATION-SPECIFIC STAGING*
BMI (kg/m2)	Clinical Component	Disease Stage	Complications
<25 (<23 in certain ethnicities)		Normal weight	None
25-29.9 (23-24.9 in certain ethnicities)	Evaluate for presence or absence of adiposity-related complications and severity of complications Asthma/reactive airway disease CVD Depression Dyslipidemia Female infertility GERD Hypertension Male hypogonadism Metabolic syndrome MAFLD OSA OA PCOS Prediabetes/T2DM Urinary stress incontinence	Overweight Stage 0	None
≥30 (≥25 in certain ethnicities)		Obesity Stage 0	None
≥25 (≥23 in certain ethnicities)		Obesity Stage 1	≥1 mild-moderate complications
		Obesity Stage 2	At least 1 severe complication
*Reference: American Association of Clinical Endocrinologists (AACE) and American College of Endocrinology (ACE) comprehensive clinical practice guidelines for medical care of patients with obesity. Endocr Pract. 2016 Jul;22 Suppl 3:1-203.

Alternatively, the Edmonton Obesity Staging System or the King’s Obesity Staging Criteria can be used to assess the impact of obesity on physical and psychological health and function. It also helps determine the benefit of treatment.