Testing for malnutrition in adults involves a combination of screening questionnaires, physical examination, blood tests, and body measurements. No single test confirms malnutrition on its own. Instead, clinicians layer several types of evidence together, starting with a quick screening tool and moving into more detailed assessments when the initial results raise concern. Around 34% of older hospital patients are classified as being at risk of malnutrition, making routine screening a critical first step that often gets overlooked.
Screening Tools: The First Step
Two validated questionnaires are used most often to flag adults who need further evaluation. Neither one diagnoses malnutrition by itself, but both are fast, require no lab work, and can be done by any trained health worker.
The Malnutrition Universal Screening Tool (MUST) is recommended for adults living in the community. It scores three things: your current BMI, any unintentional weight loss over the past three to six months, and whether an acute illness has stopped you from eating for more than five days. The first two factors each receive 0, 1, or 2 points, and acute illness adds 2 points if present. A total score of 0 means low risk, 1 means medium risk, and 2 or higher means high risk.
The Mini Nutritional Assessment Short Form (MNA-SF) is designed for older adults. It evaluates six areas: food intake, unintentional weight loss, mobility, psychological stress or acute disease, cognitive problems, and either BMI or calf circumference. Scores range from 0 to 14. A score of 12 to 14 is considered normal, 8 to 11 signals risk of malnutrition, and 0 to 7 indicates the person is likely malnourished.
Physical Examination Signs
A nutrition-focused physical exam uses a head-to-toe approach to look for visible changes that malnutrition causes in the body. Clinicians assess five main areas: muscle mass, fat stores, fluid retention (edema), signs of vitamin and mineral deficiencies, and functional capacity. Muscle wasting is one of the most telling signs. It’s often visible in the temples, the area around the collarbone, the shoulders, and the backs of the hands, where thinning tissue becomes noticeable before other body areas show changes.
Loss of subcutaneous fat shows up around the eyes (sunken appearance), on the upper arms, and over the ribs. Skin and hair changes can point to specific nutrient gaps: dry, flaky skin, slow-healing wounds, thinning hair, or unusually pale nail beds. None of these signs alone confirms malnutrition, but together they build a clinical picture that guides the next steps in testing.
Blood Tests and Their Limitations
Blood markers have traditionally played a supporting role in malnutrition assessment, though their usefulness is more limited than many people assume.
Serum albumin is the most commonly ordered test. Normal levels fall between 3.3 and 4.8 g/dL. In stable patients, low albumin can suggest chronic protein depletion, and levels below 3.5 g/dL have been linked to higher rates of surgical complications and mortality. The problem is that albumin has a half-life of about 20 days, so it responds slowly to changes in nutrition. More importantly, inflammation, liver disease, and kidney disease all drive albumin levels down independently of nutritional status. A person with pneumonia or rheumatoid arthritis may have low albumin purely because of inflammation, not because they’re malnourished.
Prealbumin is often preferred because it has a much shorter half-life of two to three days, making it a better indicator of recent nutritional changes. Levels below 10 mg/dL are associated with malnutrition, and during treatment, an increase of less than 4 mg/L per week suggests the nutritional plan isn’t working. However, prealbumin shares the same vulnerability to inflammation. Screening should ideally be done only after ruling out acute inflammation, typically by checking C-reactive protein (CRP) levels first. If CRP is elevated above 15 mg/L, prealbumin results become unreliable as a nutrition marker.
The current expert consensus treats these blood tests as complements to a thorough physical examination, not replacements for one. They add useful context, especially for tracking whether someone is improving with treatment, but they cannot diagnose malnutrition on their own.
Micronutrient Testing
When specific deficiencies are suspected, clinicians can order targeted blood panels. The most commonly tested nutrients include vitamin D, vitamin B12, folate, iron (along with ferritin and transferrin), zinc, magnesium, and calcium. Vitamin A, vitamin C, and copper may be checked in people with chronic digestive conditions that impair absorption. These tests are not routine for every patient flagged as malnourished. They’re ordered based on symptoms, dietary history, and underlying conditions that make certain deficiencies more likely.
Body Measurements
BMI remains a standard starting point. The World Health Organization classifies a BMI below 18.5 as underweight, while a BMI below 17.0 indicates thinness that has been clearly linked to increased illness across multiple populations. A BMI below 16.0 carries markedly increased risk for poor physical performance, lethargy, and death. For malnutrition diagnosis specifically, international guidelines use a BMI below 20 for adults under 70 and below 22 for adults over 70 as thresholds of concern (with slightly lower cutoffs used in Asian populations).
It’s worth noting that BMI alone can miss malnutrition in people who are overweight or obese. Someone with a BMI of 28 can still be malnourished if they’ve lost significant muscle mass or have been eating poorly for weeks. That’s why weight change over time matters more than any single measurement. Unintentional loss of more than 5% of body weight within six months, or more than 10% over a longer period, is one of the strongest indicators.
Mid-upper arm circumference, measured with a flexible tape at the midpoint of the upper arm, provides a quick estimate of muscle and fat stores. It’s particularly useful in settings where scales aren’t available or when fluid retention makes weight readings unreliable. Calf circumference serves a similar purpose in older adults and is incorporated into the MNA-SF screening tool.
Grip Strength as a Functional Test
Handgrip strength, measured with a small handheld device called a dynamometer, has gained recognition as a practical way to assess nutritional status. Muscle function declines with malnutrition often before visible wasting appears, making grip strength an early warning signal. Research in clinical populations has identified cutoff values: grip strength below 23.5 kg for men and below 14.5 kg for women is associated with higher risk of malnutrition and inflammation. Men with grip strength above that threshold had 5.7 times lower odds of being malnourished.
The test takes less than a minute. You squeeze the dynamometer as hard as you can, typically three times with your dominant hand, and the best result is recorded. It’s inexpensive, painless, and increasingly used alongside traditional assessments in hospitals and outpatient clinics.
How a Diagnosis Is Made
The Global Leadership Initiative on Malnutrition (GLIM) established the current international framework for formally diagnosing malnutrition. It requires at least one “phenotypic” criterion (something observable about the body) and at least one “etiologic” criterion (an underlying cause).
The three phenotypic criteria are:
- Weight loss: more than 5% in the past six months, or more than 10% beyond six months
- Low BMI: below 20 if under 70 years old, or below 22 if over 70
- Reduced muscle mass: confirmed through body composition measurement, physical exam, or functional testing
The two etiologic criteria are:
- Reduced food intake or absorption: eating 50% or less of energy needs for more than a week, any reduction lasting more than two weeks, or a chronic digestive condition that impairs nutrient absorption
- Inflammation or disease burden: from acute illness or injury, or from a chronic condition like cancer, heart failure, or chronic obstructive lung disease
This two-part requirement exists because malnutrition almost always has a reason behind it. Identifying the cause shapes the treatment plan. Someone malnourished from poor food access needs a different intervention than someone malnourished because inflammatory bowel disease prevents their gut from absorbing nutrients properly.
Why Inflammation Complicates Testing
Inflammation is both a cause of malnutrition and a factor that muddles test results. Chronic conditions like cancer, arthritis, diabetes, and cardiovascular disease produce ongoing low-grade inflammation that breaks down muscle, suppresses appetite, and alters how the body processes nutrients. The same inflammatory signals that cause these problems also push albumin and prealbumin levels down, making blood tests look worse than the nutritional deficit alone would explain.
This is why clinicians often check CRP alongside nutritional blood work. CRP acts as a gauge of how much inflammation is present, helping distinguish between low albumin from poor nutrition and low albumin from disease activity. Research from the large EFFORT trial found that nutritional supplementation was less effective in people with very high inflammation (CRP above 100 mg/L), suggesting that managing the underlying inflammatory condition is just as important as improving dietary intake. Stratifying patients by inflammatory status helps predict who will respond best to nutritional therapy and who needs the root cause addressed first.