CHAPTER 223 Body Fat Analysis
Body fat analysis is a quantitative method for assessing obesity and lean body mass. Several methods of body fat analysis are listed in Table 223-1, and each has advantages and disadvantages. Body fat analysis is more accurate than using body mass index (BMI) for evaluation.
Contraindications
• For MRI, patients with pacemakers, implantable defibrillators, spinal cord stimulators, or implantable pain pumps
Skin-Fold Measurements
Technique
1 Although it matters little on which side of the body measurements are taken, by convention, measurements are taken on the right side.
3 Be familiar with the skin-fold site to be measured, and pull the skin fold once or twice before the actual measurement.
4 Grasp the skin fold with the index finger and thumb of one hand and pull a fold away from the body with the sides approximately parallel. Asking the patient to contract the underlying muscle will help in grasping only skin and fat.
5 Place the caliper heads approximately 0.5 cm away from the fingers holding the skin fold. Place the caliper heads perpendicular to the skin fold and measure 4 to 5 seconds after releasing the lever arm of the calipers.
7 Take a minimum of two measurements 15 seconds apart at each site until consecutive measurements vary by no more than 1 mm, to ensure consistency.
8 Measuring obese subjects may require both hands to pull a skin fold away with parallel sides. In this case, an assistant is needed to place the caliper heads on the skin fold.
9 Take measurements when the skin is dry and when the subject is not overheated (e.g., after exercise). Vasodilation of the skin in these conditions will inflate normal skin-fold size.
Measurements at seven common sites are described as follows:
1 Chest: Pick up the pectoral skin fold at the anterior axillary line with the long axis directed to the nipple. Place the skin-fold calipers approximately 2 cm anterior to the anterior axillary line (Fig. 223-2).
2 Subscapular: Lift a diagonal fold parallel to the medial border of the scapula at a point just below the inferior angle of the scapula (Fig. 223-3).
3 Triceps: Pick up a vertical fold on the posterior arm 1 cm above the midway point between the lateral edge of the acromion and the inferior border of the olecranon. A measuring tape may be helpful in determining the midpoint (Fig. 223-4). Measurements are taken with the arm hanging loosely at the side and with the caliper heads placed precisely at the midpoint (Fig. 223-5).
5 Suprailiac: Pick up a diagonal fold along Langer’s lines above the iliac crest just posterior to the mid-axillary line, with the calipers placed approximately 1 cm anterior to the grasping fingers. The arm should hang naturally to the side but can be moved slightly to improve access (Fig. 223-7).
6 Thigh: Measure a vertical fold midway between the inguinal crease and the superior border of the patella. It may be helpful to use a measuring tape to determine the midpoint of the anterior thigh (Fig. 223-8). Pick up the skin fold 1 cm above this point. The subject should have his or her body weight shifted to the opposite side, with the measured leg in slight knee flexion and the foot flat on the floor (Fig. 223-9).
7 Medial calf: Measure a vertical fold at the level of the maximum calf circumference on the medial side of the calf. The measured leg should not bear weight and can be measured with the patient in either the standing or the seated position (Fig. 223-10).
Figure 223-4 Determining the midpoint between the lateral edge of the acromion and the inferior border of the olecranon.
Figure 223-8 Determining the midpoint of the anterior thigh between the inguinal crease and the superior border of the patella.
