Malnutrition, a state of undernutrition or overnutrition, can have profound effects on the body's physiological processes, often reflected in routine and specialized laboratory tests. Identifying these altered lab values is a crucial step in diagnosing nutritional deficiencies and monitoring the effectiveness of treatment. Laboratory findings, however, must be interpreted within the larger context of a patient's clinical history, physical exam, and inflammatory status.
Protein and Visceral Protein Markers
Serum visceral proteins are among the most common lab markers used to assess protein nutritional status. However, interpreting these markers can be complex due to the influence of inflammation.
- Albumin: Produced by the liver, albumin is the most abundant protein in the blood. Low serum albumin ($<3.5 ext{ g/dL}$) often indicates protein malnutrition but is not specific, as levels can be affected by liver or kidney disease, overhydration, and severe inflammation. Because of its long half-life (approximately 20 days), albumin is a better indicator of chronic malnutrition rather than acute changes.
- Prealbumin (Transthyretin): With a much shorter half-life (2-3 days), prealbumin is a more sensitive indicator of recent changes in protein intake and nutritional status. Normal adult levels are typically $15-30 ext{ mg/dL}$, and levels below $15 ext{ mg/dL}$ are often associated with malnutrition. Like albumin, prealbumin can also be affected by inflammation, liver function, and kidney disease.
- Transferrin: This protein transports iron and has a half-life of about 10 days. Transferrin levels may decrease in severe malnutrition but can be misleading as they increase in iron deficiency. It is also considered a negative acute-phase reactant, meaning its levels can decrease with inflammation.
Micronutrient and Vitamin Deficiencies
Malnutrition frequently involves deficiencies in essential vitamins and minerals, which can be detected through specific lab tests.
- Iron: Iron deficiency is the most common nutritional deficiency worldwide. Labs to evaluate include:
- Ferritin: Low serum ferritin is the most specific marker for iron deficiency. However, it is an acute-phase protein, and inflammation can falsely elevate its levels.
- CBC with Indices: Can show microcytic (small) and hypochromic (pale) red blood cells, indicating iron deficiency anemia.
- Transferrin Saturation: Decreased levels of transferrin saturation are seen with iron deficiency.
- Vitamin B12 and Folate: Deficiencies in these vitamins can cause megaloblastic anemia, characterized by large, immature red blood cells. Lab tests measure serum or red blood cell folate and serum B12 levels.
- Vitamin D: Measured as 25-hydroxyvitamin D [25(OH)D], a deficiency can lead to bone disorders like rickets in children and osteomalacia in adults. A level of less than $20 ext{ ng/mL}$ is often considered insufficient.
- Zinc: A deficiency can be difficult to assess via a single test but is sometimes measured in blood plasma. Hair or urine analysis may also be used. Zinc deficiency can impair immune function and wound healing.
- Copper: Copper deficiency, which can be induced by high zinc intake, is evaluated by measuring ceruloplasmin levels. Low ceruloplasmin can be a sign of copper deficiency.
Electrolyte and Metabolic Abnormalities
Malnutrition can disrupt the body's electrolyte balance and metabolic functions, which are critical to monitor.
- Electrolytes: Hypokalemia (low potassium), hypomagnesemia (low magnesium), and hypophosphatemia (low phosphate) are common, especially in cases of severe acute malnutrition and during refeeding syndrome. Refeeding syndrome is a potentially fatal shift in fluids and electrolytes when a severely malnourished person is reintroduced to food too quickly.
- Renal Function Tests: Blood urea nitrogen (BUN) and creatinine are often lower in malnourished individuals due to reduced protein intake and decreased muscle mass. This can mask underlying kidney dysfunction, necessitating careful interpretation. Severe malnutrition can also impair glomerular filtration rate and other renal functions.
- Liver Function Tests (LFTs): Severe malnutrition can cause abnormalities in LFTs, including elevated levels of transaminases (ALT, AST), which can sometimes worsen temporarily during refeeding. However, these abnormalities often reverse with nutritional support.
- Lipid Profile: Undernourished individuals may have low cholesterol levels.
Hematological Indicators
Malnutrition can significantly affect the components of a complete blood count (CBC).
- Complete Blood Count (CBC): A CBC with red blood cell indices is a key tool for detecting anemia related to nutritional deficiencies (e.g., iron, folate, B12).
- Total Lymphocyte Count: Chronic malnutrition can lead to lymphopenia, a low lymphocyte count, reflecting an impaired immune response.
Comparison of Key Nutritional Markers
| Feature | Albumin | Prealbumin | Transferrin | Ferritin |
|---|---|---|---|---|
| Half-Life | ~20 days | 2-3 days | ~10 days | Varies |
| Indicates | Chronic protein status | Acute protein status | Protein and iron status | Iron stores |
| Effect of Inflammation | Decreases | Decreases | Decreases | Increases |
| Effect of Liver Disease | Decreases | Decreases | Decreases | Increases or no change |
| Effect of Renal Disease | Can decrease | Can increase | Can increase | Increases or no change |
| Monitoring | Less sensitive for rapid changes | Better for monitoring rapid changes | Affected by iron status | Needs interpretation with CRP |
Conclusion
Multiple laboratory tests are affected by malnutrition, providing valuable insights into a patient's nutritional status. These include protein markers (albumin, prealbumin), micronutrient levels (iron, vitamins, zinc), electrolytes, liver and renal function, and hematological parameters. However, no single test can definitively diagnose malnutrition. Inflammation, liver or kidney disease, and hydration status can all influence results, making a comprehensive nutritional assessment—including clinical signs and patient history—essential. Laboratory data should be used as a supportive tool to identify deficiencies, monitor the effectiveness of nutritional interventions, and screen for potential complications like refeeding syndrome. Interpreting these complex lab values correctly is paramount for providing safe and effective patient care. For more information on interpreting nutritional lab markers, authoritative resources such as reviews from organizations like the European Society for Clinical Nutrition and Metabolism (ESPEN) can be consulted An authoritative review on nutritional biomarkers.
