What is the diagnosis of malnutrition?

October 13, 2025 •

3 min read

Malnutrition affects millions worldwide and is defined as deficiencies, excesses, or imbalances in a person's intake of energy and/or nutrients. The diagnosis of malnutrition involves a systematic evaluation of a patient's overall nutritional status, moving beyond simple weight checks to a comprehensive assessment.

Quick Summary

This guide details the diagnostic criteria for malnutrition, covering assessment techniques like anthropometric measurements, biochemical tests, and clinical evaluation. It also outlines the different diagnostic tools used for adults and children and explains the signs and symptoms of undernutrition and overnutrition.

Key Points

Screening Tools: Use validated tools like MUST (Malnutrition Universal Screening Tool) or MNA (Mini Nutritional Assessment) for initial risk identification.
Clinical Evaluation: A physical examination can reveal telltale signs such as muscle wasting, loss of subcutaneous fat, hair changes, and skin abnormalities.
Anthropometric Measurements: Weight, height, BMI, and body composition measurements are essential for assessing overall nutritional status and tracking changes.
Biochemical Tests: Laboratory tests for markers like albumin, prealbumin, and micronutrients help identify specific deficiencies and inflammation.
GLIM Criteria: The Global Leadership Initiative on Malnutrition provides a consensus framework for diagnosis in adults, requiring at least one phenotypic and one etiologic criterion.
Undernutrition vs. Overnutrition: Malnutrition includes both deficiencies (undernutrition) and excesses (overnutrition, or obesity), and a proper diagnosis must consider all forms.
Child Malnutrition: Diagnosis in children relies on specific growth standards (e.g., WHO growth charts) and measurements like weight-for-height, weight-for-age, and MUAC.

The Diagnostic Process for Malnutrition

Diagnosing malnutrition is a multi-step process that typically begins with screening to identify individuals at risk, followed by a more detailed assessment. Malnutrition encompasses various forms, including undernutrition, micronutrient deficiencies, and overnutrition. A comprehensive diagnosis requires combining clinical history, physical examination, and potentially laboratory testing.

Step 1: Nutritional Screening

Initial screening is crucial, especially in clinical settings, to identify individuals requiring further assessment. Common validated tools include:

Malnutrition Universal Screening Tool (MUST): Evaluates BMI, weight loss, and acute disease effect to determine a risk score.
Mini Nutritional Assessment (MNA): Tailored for older adults (≥65 years), assessing dietary intake, weight loss, mobility, and cognitive issues.
Nutritional Risk Screening 2002 (NRS-2002): Recommended for clinical settings, it considers disease severity and nutritional status to determine risk.

Screening helps pinpoint those who need a more in-depth nutritional assessment to confirm a diagnosis.

Step 2: Comprehensive Nutritional Assessment

A detailed assessment is performed for at-risk individuals, often by a registered dietitian. This assessment includes:

Clinical History: Gathering information on diet, recent illnesses, and symptoms like changes in appetite, chewing/swallowing difficulties, or GI issues.
Physical Examination: Looking for clinical signs such as changes in hair, skin, loss of subcutaneous fat and muscle, or edema.
Anthropometric Measurements: Physical measurements compared to standards to evaluate nutritional status.
- Adults: Height, weight, BMI, mid-upper arm circumference (MUAC), and skinfold thickness are used.
- Children: Weight, length, and head circumference plotted on growth charts are used, with height and weight for older children.

Step 3: Biochemical and Body Composition Analysis

Laboratory tests provide important data on nutrient levels and inflammation.

Routine Blood Tests: Can detect anemia, electrolyte imbalances, and deficiencies in micronutrients like iron or vitamin B12.
Protein Status Markers: Serum albumin indicates long-term protein status, while prealbumin and retinol-binding protein show more recent changes.
Inflammatory Markers: C-reactive protein (CRP) may be measured to assess systemic inflammation, a factor in malnutrition.
Body Composition Studies: Techniques like BIA or DEXA provide objective data on fat-free and fat mass.

Global Leadership Initiative on Malnutrition (GLIM) Criteria

The GLIM consensus proposed a standardized scheme for adult malnutrition diagnosis. It involves screening and assessment using GLIM criteria, which require at least one phenotypic criterion (weight loss, low BMI, or reduced muscle mass) and one etiologic criterion (reduced intake or inflammation/disease). This framework also allows for grading the severity of malnutrition.

Comparison of Malnutrition Diagnostic Approaches


Feature	Global Leadership Initiative on Malnutrition (GLIM)	Academy/ASPEN Consensus Criteria	Malnutrition Universal Screening Tool (MUST)
Target Population	Adults	Adults (hospital and community)	All adults (especially older)
Diagnostic Approach	Two-step: screening followed by assessment using specific phenotypic and etiologic criteria.	At least two of six characteristics (weight loss, energy intake, fat/muscle loss, fluid accumulation, grip strength).	Five-step scoring based on BMI, weight loss, and acute disease.
Key Criteria	Weight loss, low BMI, reduced muscle mass (phenotypic); Reduced intake, inflammation (etiologic).	Inadequate energy intake, weight loss, muscle mass loss, fat loss, fluid accumulation, reduced grip strength.	BMI, percentage of unplanned weight loss, acute disease score.
Advantages	Standardized, considers both physical and underlying causes. Severity can be graded.	Specific criteria allow for detailed assessment and classification based on etiology.	Simple and rapid, widely used for initial screening in various settings.
Limitations	Requires more data collection than simple screening. Requires validation studies.	Some criteria like body fat and muscle loss require clinical judgment.	Designed for screening, not for in-depth diagnostic assessment or identifying specific micronutrient issues.

Conclusion

The diagnosis of malnutrition is a comprehensive process that begins with screening using tools like MUST or MNA to identify individuals at risk. A full nutritional assessment, guided by frameworks such as GLIM for adults, follows for those identified as at-risk. This assessment incorporates clinical signs, anthropometric measurements, and biochemical analysis to provide a complete picture of the patient's nutritional status. Accurate and timely diagnosis is vital for implementing appropriate nutritional interventions to improve patient outcomes.

Frequently Asked Questions

The initial signs can be subtle and include unintentional weight loss, a noticeable loss of appetite, persistent fatigue, and irritability. Clothing, watches, or rings may also become looser over time.

Yes, it is possible to be overweight or obese and still suffer from malnutrition, a condition sometimes called 'overnutrition'. This occurs when a person has excess calories but a deficiency in essential micronutrients, like vitamins and minerals, which can also lead to adverse health effects.

Diagnosis in children typically involves plotting their weight, height/length, and head circumference on standardized growth charts (like WHO or CDC charts) to check for deviations from expected growth patterns, such as wasting or stunting. A mid-upper arm circumference (MUAC) measurement is also a key indicator, particularly for severe acute malnutrition.

The GLIM (Global Leadership Initiative on Malnutrition) criteria provide a globally recognized, standardized framework for diagnosing malnutrition in adults. It requires a patient to meet at least one phenotypic criterion (e.g., weight loss, low BMI) and one etiologic criterion (e.g., reduced food intake, inflammation) for a confirmed diagnosis.

Yes, blood tests are used to assess general nutritional status and can reveal specific deficiencies. Common tests include a complete blood count (CBC) to check for anemia, and measurements of specific micronutrients like iron, vitamin B12, and folate. While not perfect markers, protein levels like albumin and prealbumin may also be evaluated, along with inflammatory markers like C-reactive protein (CRP).

Severe malnutrition can present with pronounced physical signs. These include visible muscle wasting around the temples, collarbones, and thighs, loss of fat, edema (swelling) in the legs or abdomen, and changes to hair and skin, such as easy hair plucking or thin, flaky skin.

A comprehensive assessment is essential because malnutrition can result from many different underlying causes, including inadequate intake, malabsorption, or increased metabolic needs due to illness. It moves beyond simple weight readings to understand the full clinical picture, which is critical for developing an appropriate and effective treatment plan.