Malnutrition

Malnutrition means the body isn't getting the right amount of energy, protein, vitamins or minerals. It usually refers to undernutrition, though excess intake is also a form of malnutrition. Undernutrition is common in older adults, people with long-term illnesses, cancer, gut conditions that affect absorption, eating difficulties, depression, alcohol use disorder, and people in hospital or care homes. Signs include unintended weight loss, loss of muscle, tiredness, weakness, frequent infections, slow wound healing, and feeling cold. It raises the risk of falls, complications and longer recovery from illness.

Lab tests linked to malnutrition:

• Transferrin: an iron-carrying protein made by the liver. It can be low with poor protein intake, but also with inflammation and liver disease.
• Malnutrition is diagnosed with a nutrition assessment covering weight history, body mass index, muscle mass, food intake and illness. Tools such as MUST screen for risk, while the GLIM criteria help establish the diagnosis. Doctors may also order albumin, prealbumin, a CBC, electrolytes including phosphate and magnesium, kidney and liver tests, and levels of vitamins and minerals such as B12, folate, vitamin D, iron and zinc.

How results are read:

• Albumin, prealbumin and transferrin fall with inflammation and illness, so they are not reliable markers of nutrition on their own.
• Low B12, folate, iron or vitamin D point to specific deficiencies that need treatment.
• Low phosphate, potassium or magnesium in someone who has eaten very little are warning signs for refeeding syndrome, a dangerous shift in electrolytes when feeding restarts.

When to see a doctor:

• See a doctor about unintended weight loss of more than 5% in 6 months, poor appetite that lasts, or difficulty eating or swallowing.
• If an older relative is losing weight or eating less, ask about a nutrition assessment.
• Get emergency care for confusion, severe weakness, fainting or an irregular heartbeat in someone who is severely underweight.

Clinical takeaway: malnutrition is diagnosed with a nutrition assessment, and blood tests find specific deficiencies and risks rather than measuring nutrition directly.