What is Triceps Skinfold (TSF) Thickness?
Triceps skinfold (TSF) thickness is a non-invasive anthropometric measurement that quantifies the amount of subcutaneous fat located on the back of the upper arm. As approximately 50% of the body's total fat is subcutaneous, the TSF provides a valuable estimate of overall body fat reserves, which are crucial energy stores. For this reason, severely reduced TSF thickness is a strong indicator of severe malnutrition, particularly Protein-Energy Malnutrition (PEM).
Measuring TSF involves using specialized calipers, such as Harpenden or Lange models, to pinch a fold of skin and fat. The measurement is typically taken at the midpoint of the upper arm, midway between the acromion process (at the shoulder) and the olecranon process (at the elbow). A highly trained professional is required to perform this measurement consistently, as technique can significantly impact the precision of the results. Repeated measurements are essential for monitoring changes in a patient's nutritional status over time.
Interpreting TSF for Severe Malnutrition
Interpretation of TSF measurements relies heavily on comparing the patient's value to reference standards that are specific to age and gender. These reference standards are typically presented in percentile tables derived from large, healthy populations. A low percentile indicates a low fat reserve and potential malnutrition. For instance, being below the 15th percentile often suggests a state of malnutrition, while a measurement at or below the 5th percentile is indicative of significant fat depletion and a high degree of nutritional risk.
Severe malnutrition is characterized by a significant loss of body fat and muscle mass. As TSF primarily measures fat, a very low TSF reading points to the depletion of the body's energy stores. However, TSF is just one component of a comprehensive nutritional assessment. It is often evaluated alongside other measures, such as mid-upper arm circumference (MUAC), to gain a more complete picture of both fat and muscle reserves.
Pediatric versus Adult Standards
The percentile cutoff points that indicate severe malnutrition differ markedly between children and adults, reflecting normal developmental growth patterns. In pediatric nutrition, classifications for wasting (low weight-for-height) and stunting (low height-for-age) use z-scores relative to WHO child growth standards. While specific TSF cutoffs for severe malnutrition in children also reference percentiles, emergency screening for Severe Acute Malnutrition (SAM) often relies on MUAC tapes for their ease of use in community settings. In adults, consensus criteria for malnutrition may combine TSF results with body mass index (BMI) and unintentional weight loss.
- Pediatric population: For children under 5, a MUAC of less than 115mm is a widely used screening tool for SAM, although some research suggests that gender and age-specific cutoffs could improve sensitivity. For TSF, reference standards like those published by A.R. Frisancho in 1981 provide age- and gender-specific percentiles, with values below the 15th percentile suggesting malnutrition.
- Adult population: A TSF measurement at or below the 5th percentile is typically considered indicative of severe malnutrition or high nutritional risk. Factors like age and underlying disease can influence TSF readings and their interpretation. For instance, a Chinese study found that a low TSF thickness trajectory was associated with a higher mortality risk in men and non-elderly women.
Comparison with Other Nutritional Markers
Anthropometry, the science of human body measurement, uses a variety of tools to assess nutritional status. TSF is a valuable part of this toolkit but has certain limitations. For example, MUAC is often preferred in acute emergency settings for screening purposes because of its simplicity, cost-effectiveness, and ease of use in the field. However, combining measurements can offer a more detailed and reliable assessment.
| Assessment Method | Target Indicator | Interpretation for Malnutrition | Strengths | Weaknesses |
|---|---|---|---|---|
| Triceps Skinfold (TSF) | Subcutaneous fat reserves | Significantly reduced fat stores; values below the 5th percentile indicate high risk. | Easy, inexpensive, good indicator of fat stores. | High inter-examiner variability; requires specialized calipers; not reliable for short-term changes. |
| Mid-Upper Arm Circumference (MUAC) | Fat and muscle reserves | MUAC below established cutoffs (e.g., <115mm for young children) indicates SAM. | Simple, quick, and ideal for screening in community settings. | Less precise than multi-parameter assessments; less useful for chronic conditions. |
| Body Mass Index (BMI) | Weight-for-height | BMI <18.5 kg/m² for adults is a common malnutrition indicator. | Widely used, provides an overall weight-for-height picture. | Does not differentiate between fat and muscle mass; less sensitive to subtle changes. |
| Subjective Global Assessment (SGA) | Clinical history and physical exam | Categorizes patients as well-nourished, moderately, or severely malnourished based on history and fat/muscle loss. | Clinically practical, incorporates subjective and objective data. | Subject to inter-rater reliability; less quantitative than direct measurements. |
Practical Application of TSF
For severe malnutrition, the most direct interpretation is a TSF measurement that falls significantly below the 5th percentile for the individual's age and sex. A key advantage of using TSF alongside other measures is the ability to track trends over time. Repeated measurements can show if a patient's nutritional status is deteriorating or improving with treatment. This is critical for managing malnutrition in both hospital and long-term care settings.
Conclusion
Triceps skinfold thickness is a clinically relevant, accessible tool for assessing body fat and diagnosing severe malnutrition, especially when interpreted against age- and gender-specific percentiles. While it is particularly useful for tracking changes in body composition over time, it is most effective as part of a multi-parameter assessment, combining with other indicators like MUAC and BMI for a comprehensive and accurate diagnosis. A TSF reading at or below the 5th percentile is generally considered indicative of severe nutritional risk. Proper technique and the use of standardized percentile charts are crucial for reliable results and effective management of malnourished patients.
Optional Outbound Link
For a deeper understanding of anthropometric measurements and body composition, consult the resource from Principles of Nutritional Assessment.
