Malnutrition develops when the body is deprived of the nutrients it needs to function properly, encompassing both undernutrition and dietary imbalances. While physical signs like weight loss can signal a problem, blood tests offer a more definitive view. They provide objective data that can confirm a diagnosis and pinpoint specific deficiencies, revealing a detailed picture of a person’s nutritional status.
Protein Status Markers
Protein levels in the blood serve as indicators of nutritional status. Albumin is the most plentiful protein in blood plasma and is used to assess long-term nutritional health. Because it has a long half-life of about 20 days, its concentration changes slowly, meaning low albumin levels often point to a chronic period of poor nutrition. Levels below 3.5 g/dL are a common cutoff point suggesting malnutrition.
A more sensitive marker for short-term nutritional changes is prealbumin, also known as transthyretin. With a half-life of only two to three days, its levels reflect recent dietary intake much more quickly than albumin. This makes it useful for monitoring a patient’s nutritional recovery. A concentration below 10 mg/dL is often considered a sign of significant malnutrition.
The interpretation of protein markers is complex, as inflammation can also lower their levels. The body’s inflammatory response can suppress the liver’s production of albumin and prealbumin, even if nutritional intake is adequate. To account for this, clinicians often measure C-reactive protein (CRP). If CRP is elevated, low protein levels may be attributed to inflammation rather than malnutrition.
Micronutrient Indicators
Beyond proteins, blood tests are essential for identifying deficiencies in micronutrients, which are the vitamins and minerals the body needs in smaller quantities. Among the most commonly tested vitamins are vitamin D, vitamin B12, and folate (B9). Vitamin D is important for bone health and immune function, while B12 and folate are necessary for producing red blood cells and for neurological function.
Blood tests also reveal the status of key minerals that are often depleted in cases of malnutrition. Iron levels are evaluated by measuring serum ferritin, a protein that stores iron. Low ferritin indicates that the body’s iron reserves are exhausted, a condition that precedes the development of iron-deficiency anemia. Other minerals like zinc and magnesium are also assessed to get a complete picture.
Complete Blood Count and Anemia
A complete blood count (CBC) provides a broad overview of blood health. It does not measure nutrients directly but instead reveals how nutritional deficiencies are affecting the production and characteristics of blood cells. The CBC is often one of the first tests ordered when malnutrition is suspected because its results can point toward specific underlying problems and guide more targeted testing.
One of the most common findings in a malnourished individual is anemia, a condition characterized by a low number of red blood cells or a lack of hemoglobin. The CBC measures hemoglobin (Hgb) and hematocrit (Hct) to diagnose anemia. These measurements can signal that the body lacks the necessary building blocks, such as iron or certain vitamins, to produce an adequate supply of healthy red blood cells.
The CBC also provides details about the red blood cells themselves, which can help identify the cause of the anemia. The mean corpuscular volume (MCV) is a measurement of the average size of the red blood cells. Abnormally small red blood cells (microcytic anemia) often suggest iron deficiency, while unusually large red blood cells (macrocytic anemia) typically point toward a deficiency in vitamin B12 or folate.
Interpreting the Results
The process of diagnosing malnutrition is complex, and healthcare professionals rarely depend on a single test result. Instead, they analyze the pattern of results across multiple tests, viewing them in the context of a patient’s overall health and history. A comprehensive assessment combines laboratory data with a physical examination and patient history to form a complete clinical picture.
Several physiological factors can influence blood test results. A person’s hydration status is one such factor, as dehydration can concentrate substances in the blood, leading to falsely elevated levels of markers like albumin.
Co-existing diseases can also complicate the interpretation of nutritional markers. For example, chronic liver disease can impair the liver’s ability to produce proteins like albumin, while kidney disease can cause protein to be lost in the urine. In these cases, low protein levels may be a result of the disease process itself, rather than inadequate dietary intake. Ultimately, blood tests are tools that, when interpreted correctly by a professional, help guide the creation of a personalized nutritional plan.