Obesity Workup

Updated: Mar 02, 2017
  • Author: Osama Hamdy, MD, PhD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Workup

Approach Considerations

Standard laboratory studies in the evaluation of obesity should include the following:

  • Fasting lipid panel
  • Liver function studies
  • Thyroid function tests
  • Fasting glucose and hemoglobin A1c (HbA1c)

Other tests are performed as indicated by clinical findings. For example, the 24-hour urinary free-cortisol test is needed only when Cushing syndrome or other hypercortisolemic states are clinically suspected. However, approximately 4% of patients with Cushing syndrome have normal urinary free-cortisol values.

Lipid panel

At minimum, test fasting cholesterol, triglycerides, and high-density lipoprotein cholesterol (HDL-C) levels. These levels may be normal, or the typical dyslipidemia associated with cardiometabolic syndrome may be found. This dyslipidemia is characterized by reduced HDL-C and elevated fasting triglyceride concentrations; however, increased low-density lipoprotein cholesterol (LDL-C) and normal to marginally increased total cholesterol are not uncommon among obese individuals.

Liver and thyroid function tests

Liver function tests yield normal results in most obese patients. However, elevated transaminase levels may indicate nonalcoholic steatohepatitis (NASH) or fatty infiltration of the liver).

Thyroid function test results are also typically normal, but checking them to detect primary hypothyroidism (characterized by increased serum thyrotropin and normal or reduced thyroxine and/or triiodothyronine levels) is worthwhile. Screening with a serum thyrotropin level is usually sufficient. Of importance, hypothyroidism itself rarely causes more than mild obesity.

Glucose and insulin studies

Obesity is associated with insulin resistance and increased serum levels of fasting insulin and C-peptide serum levels. However, insulin levels are normal in many persons who are obese.

All patients with obesity should be screened for diabetes. Additional information is gained by using glucose and HbA1c tests together if the patient is fasting. The American Diabetes Association currently recommends using the HbA1c test not only to screen for diabetes, but also to follow patients who already have the diagnosis. [19] In contrast, the American Association of Clinical Endocrinologists recommends that HbA1c be considered an additional, optional diagnostic criterion. [79]

Prediabetes is indicated by impaired fasting glucose (fasting plasma glucose levels of 100-125 mg/dL [5.6-6.9 mmol/L]) or impaired glucose tolerance (2-h oral glucose tolerance test values of 140-199 mg/dL [7.8-11.0 mmol/L]). Patients with these findings are at relatively high risk for the future development of diabetes. Type 2 diabetes is diagnosed when the fasting glucose is 126 mg/dL or greater or HbA1c is 6.5% or higher. [80]

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Evaluation of Degree of Fat

Body mass index (BMI) calculation, waist circumference, and waist/hip ratio are the common measures of the degree of body fat used in routine clinical practice. Other procedures that are used in few clinical centers include the following:

  • Caliper-derived measurements of skin-fold thickness
  • Dual-energy radiographic absorptiometry (DEXA)
  • Bioelectrical impedance analysis
  • Ultrasonography to determine fat thickness
  • Underwater weighing

The standard techniques for measuring visceral fat are magnetic resonance imaging (MRI) and computed tomography (CT) scanning. Less expensive techniques for direct measurement of visceral fat include abdominal ultrasonography and abdominal bioelectrical impedance.

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