• What is assessed?
• How is the measurement conducted?
• When is this method used?
• How are estimates of body composition derived?
• Strengths and limitations
• Populations
• Further considerations
• Resources required
• Instrument library
• References

Abdominal sagittal diameter (ASD) is the distance from the lower back to the highest point of the abdomen. It measures the anteroposterior diameter of the abdomen.

A simple and inexpensive method for the assessment of abdominal obesity, ASD has been shown to have strong associations with glucose intolerance, cardiovascular risk and mortality independent of other anthropometric measures.

ASD measurement can be combined with other anthropometry to predict visceral fat and subcutaneous fat using published validated equations.

ASD is commonly measured using an abdominal caliper with a moveable arm, such as the Holtain-Kahn Abdominal Caliper. Calibration of the caliper should be carried out at regular intervals, using rods of predetermined lengths or an instrument similar to this calliper checking gauge. ASD can also be measured using a CT or MRI scan (the gold standard for measuring different fat compartments); however these methods are limited to practical and ethical constraints. Laser beam devices have also been used in children and adolescents, a technique much favourable in these groups as no body contact is required.

Protocol using abdominal caliper

1. Before taking the measurement, it is important to identify where the measurement will be taken from and to mark this location; locate the right iliac crest at the point where it intersects the midaxillary line and with a cosmetic pencil draw a line perpendicular to the table on the uppermost lateral border of the right ilium (NHANES, 2013).
2. ASD is then measured when the participant is lying in the supine position on a flat and firm, or slightly padded, examination table with the hips in a relaxed position. The knees should be bent at a 90º angle, feet should be flat on the table and arms crossed over the chest.
3. The lower arm of the caliper should be slid gently under the small of the back, and the upper arm should be aligned with the location mark.
4. The upper arm should lightly touch the abdomen, without compressing it and the ASD measurement should be read directly from the caliper scale after normal expiratory movement.
5. Measurements should be taken to the nearest 0.1mm.
6. Two measurements should be taken and if they differ by <0.5cm a third should be taken.
7. Some abdominal calipers have a spirit level on the top of the vertical beam to indicate whether the measurement is taken on a flat surface – this should be as close to the centre as possible, but it is acceptable if it is slightly off-centre.

Figure 1 Measuring abdominal sagittal diameter.
Source: NHANES Anthropometry Procedures Manual (2013). [3]

Abdominal sagittal diameter is typically used to estimate the amount of visceral fat in both clinical setting and within epidemiological research. It is a simpler, cheaper and less invasive (while still reliable) method than CT and MRI.

Abdominal thickness measurements are typically recorded in cm, and often the raw values are used on their own as they act as an indicator of total abdominal fatness. However, they can be combined with other anthropometric measures (including waist circumference, abdominal diameter, hip circumference and skinfolds) and entered into validated equations to estimate visceral and or subcutaneous fat. A circumference tape can be used for the waist, hip and thigh measurements and skinfold calliper for the skinfold thickness.

Several published equations are available; some of the most commonly used are listed below.

Pinter et al. (2017)

1. Male visceral fat area (mm²) = 81.937 x hip circumference (mm) – 69.912 x calf circumference (mm) +48407.310 x WHR – 84219.425
2. Female visceral fat area (mm²) = 127.737 x abdominal sagittal diameter (mm) – 28.849 x thigh circumference (mm) + 341.248 x triceps skinfold (mm) + 25516.362 x WHR – 32803.778

Samouda et al. (2013)

1. Male visceral adipose tissue = 6 x waist circumference – 4.41 x proximal thigh circumference + 1.19 x age – 213.65
2. Female visceral adipose tissue = 2.15 x waist circumference – 3.63 x proximal thigh circumference + 1.46 x age + 6.22 x BMI – 92.713
3. In this particular study, including ASD in the model explained about 86% of the visceral fat variance in women and about 79% in women while substituting ASD for waist circumference explained about 84% in women and about 80.5% in men. Therefore the authors chose to substitute ASD for waist circumference due to the easier feasibility of the waist circumference measurement.

He et al. (2004) based on MRI measurements of ASD

1. Circular Model; total abdominal area = WC²/4π, and visceral compartment area = π(WC/2π – T_F)²
2. Elliptical Model; total abdominal area = πD_APD_RL/4, and visceral compartment area = π(D_AP – T_F – T_B)(D_RL – T_R – T_L)/4
3. D_AP is abdominal sagittal diameter, and D_RL is the abdominal width
4. These equations use 4 subcutaneous adipose tissue thicknesses derived from MRI; in the front (T_F), back (T_B), right (T_R) and left (T_L)

Raw and derived estimates should be quality checked during data processing in the same manner as other health related variables, for example checking for outliers and data entry errors.

An overview of the characteristics of abdominal sagittal diameter methods is outlined in Table 1.

Strengths

1. Inexpensive
2. Non-invasive
3. Limited burden to participant
4. Limited burden to researcher in terms of collection and analysis
5. Requires no input from participant and therefore no risk of respondent bias
6. Simple marker of adiposity
7. Highly correlated with visceral fat volumes measures by reference methods (correlation coefficient between 0.5-0.9)
8. ASD has been found to inversely correlate more with insulin sensitivity (Riserus et al, 2004) and cardiovascular risk (Ohrvall et al, 2000) than to other anthropometric measures such as BMI and waist circumference. As insulin resistance can predict type 2 diabetes and cardiovascular disease, the ASD measurement may be useful in identifying those individuals at risk of developing these conditions.

Limitations

1. Can be challenging to identify the correct anatomical site for the measurement, especially in obese individuals
2. Compression of the upper arm onto the abdomen can affect results and reliability
3. Subject to intra- and inter-observer variations
4. Measurement depends on muscle mass, bone structure, laxity of abdominal muscles, fasting state, respiration and posture of the participant
5. Standardisation of measurement site protocol is not always available making cross-study comparisons and harmonisation difficult
6. May be more predictive of visceral fat in leaner individuals than in obese individuals
7. The use of this measure as a tool for assessing abdominal obesity, compared with the simpler waist circumference, maybe questionable as the two measurements are highly correlated with each other and the waist circumference is an easier and a more cost effective method to carry out, and a comparable predictor of health outcomes.

Table 1 Characteristics of abdominal sagittal diameter methods.

Considerations relating to the use of abdominal sagittal diameter methods in specific populations are described in Table 2.

Table 2 Use of abdominal sagittal diameter methods in different populations.

It is recommended to estimate the technical error of measurement to monitor intra- and inter-observer variation.

Refer to section: practical considerations for objective anthropometry

1. Abdominal caliper (in cms)
2. Data entry form in either paper or electronic form
3. Training of staff required
4. Standard operating procedures for data collection
5. Standard operating procedures for data entry errors/extreme values/data cleaning
6. Toys (like bubbles) if measuring younger children

A method specific instrument library is being developed for this section. In the meantime, please refer to the overall instrument library page by clicking here to open in a new page.

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2. My Healthy Waist. Sagital Diameter, Health Risk and Intra-abdominal Fat. 2017.
3. National Health and Nutrition Examination Survey (NHANES). Anthropometry Procedures Manual 2013 [19/10/2017]. Available from: https://www.cdc.gov/nchs/data/nhanes/nhanes_13_14/2013_Anthropometry.pdf.
4. Ohrvall M, Berglund L, Vessby B. Sagittal abdominal diameter compared with other anthropometric measurements in relation to cardiovascular risk. Int J Obes Relat Metab Disord. 2000 Apr;24(4):497-501. PubMed PMID: 10805508. Epub 2000/05/11. eng.
5. Pinter Z, Posa, A., Warga, C., Horvath, I., Palko, A., Just, Z., Palfi, G.,. Anthropometric dimensions provide reliable estimates of abdominal adiposity: A validation study. Journal of Comparative Human Biology 2017.
6. Riserus U, Arnlov J, Brismar K, Zethelius B, Berglund L, Vessby B. Sagittal abdominal diameter is a strong anthropometric marker of insulin resistance and hyperproinsulinemia in obese men. Diabetes Care. 2004 Aug;27(8):2041-6. PubMed PMID: 15277437. Epub 2004/07/28. eng.
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8. Samouda H, Dutour A, Chaumoitre K, Panuel M, Dutour O, Dadoun F. VAT=TAAT-SAAT: innovative anthropometric model to predict visceral adipose tissue without resort to CT-Scan or DXA. Obesity (Silver Spring). 2013 Jan;21(1):E41-50. PubMed PMID: 23404678. Pubmed Central PMCID: 3618381. Epub 2013/02/14. eng.
9. Sjöström L, Lönn L, Chowdhury B, Grangård U, Lissner L, Sjöström D, et al. The sagittal diameter is a valid marker of the visceral adipose tissue volume. Progress in obesity research. 1996;7:309-19.
10. Van der Kooy K, Leenen R, Deurenberg P, Seidell JC, Westerterp KR, Hautvast JG. Changes in fat-free mass in obese subjects after weight loss: a comparison of body composition measures. Int J Obes Relat Metab Disord. 1992 Sep;16(9):675-83. PubMed PMID: 1328092. Epub 1992/09/01. eng.
11. Vasques ACJ, Rosado LEFPdL, Rosado GP, Ribeiro RdCL, Franceschini SdCC, Geloneze B, et al. Diferentes aferições do diâmetro abdominal sagital e do perímetro da cintura na predição do HOMA-IR. Arquivos Brasileiros de Cardiologia. 2009;93:511-8.