🍽️nutrition assessment review
5.2 Micronutrient Status Indicators
4 min read•Last Updated on July 30, 2024
Iron status is crucial for overall health, affecting everything from energy levels to cognitive function. Biochemical markers like serum ferritin, transferrin saturation, and hemoglobin help assess iron stores and detect deficiencies or overload conditions.
Micronutrient status indicators go beyond iron, covering vitamins like D and B1. These markers, such as 25(OH)D for vitamin D and RBC transketolase for thiamin, provide valuable insights into nutritional health and guide interventions.
Biochemical Markers for Iron Status
Serum Ferritin: The Gold Standard
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Top images from around the web for Serum Ferritin: The Gold Standard
Frontiers | The Clinical Significance of Iron Overload and Iron Metabolism in Myelodysplastic ... View original
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Frontiers | Inherited Disorders of Iron Overload View original
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Frontiers | Dietary Intake, Body Composition and Iron Status in Experienced and Elite Climbers View original
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Frontiers | The Clinical Significance of Iron Overload and Iron Metabolism in Myelodysplastic ... View original
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- Serum ferritin is the most sensitive and specific indicator of iron stores in the body, reflecting the amount of iron stored in the liver, spleen, and bone marrow
- Not affected by recent iron intake, making it more reliable than serum iron
- Low levels (<12-15 µg/L) indicate depleted iron stores and diagnose iron deficiency before anemia develops
- High levels (>200-300 µg/L) suggest iron overload conditions (hereditary hemochromatosis, chronic liver disease, excessive supplementation)
Other Markers of Iron Status
- Serum iron measures the amount of iron bound to transferrin in the blood
- Affected by recent iron intake, making it less reliable than serum ferritin
- Total iron-binding capacity (TIBC) measures the maximum amount of iron that can be bound by transferrin
- Increased in iron deficiency and decreased in iron overload conditions
- Transferrin saturation is calculated by dividing serum iron by TIBC and expressed as a percentage
- Reflects the proportion of transferrin carrying iron and decreased in iron deficiency
- Serum transferrin receptor (sTfR) measures iron deficiency at the cellular level
- Increased in iron deficiency as cells upregulate transferrin receptors to increase iron uptake
- Hemoglobin and hematocrit are non-specific indicators of iron status
- Affected by other factors (blood loss, pregnancy, altitude) but commonly used as anemia screening tools
Serum Ferritin for Iron Stores
Ferritin's Role in Iron Storage
- Serum ferritin is a protein that stores iron and releases it in a controlled fashion
- Direct reflection of the amount of iron stored in the body's tissues (liver, spleen, bone marrow)
- Levels not affected by recent iron intake, making it more reliable than serum iron
Interpreting Serum Ferritin Levels
- Low levels (<12-15 µg/L) indicate depleted iron stores and diagnose iron deficiency before anemia develops
- High levels (>200-300 µg/L) suggest iron overload conditions
- Hereditary hemochromatosis
- Chronic liver disease
- Excessive iron supplementation
- Serum ferritin is an acute-phase reactant elevated by inflammation, infection, or liver disease
- Can mask underlying iron deficiency
- Interpret with other markers of iron status and inflammation
Vitamin D Metabolites for Status
Vitamin D Forms and Metabolism
- Vitamin D exists as D2 (ergocalciferol) and D3 (cholecalciferol)
- Both forms metabolized in the liver to 25-hydroxyvitamin D (25(OH)D), the major circulating form
- Serum 25(OH)D best indicates vitamin D status, reflecting dietary intake and endogenous synthesis from sunlight
- 25(OH)D further metabolized in kidneys to active 1,25-dihydroxyvitamin D (1,25(OH)2D)
- Regulates calcium and phosphorus metabolism
- Tightly regulated levels do not reflect vitamin D status
Vitamin D Deficiency and Insufficiency
- Deficiency defined as serum 25(OH)D <20 ng/mL (50 nmol/L)
- Insufficiency defined as levels between 21-29 ng/mL (52.5-72.5 nmol/L)
- Optimal levels ≥30 ng/mL (75 nmol/L)
- Deficiency impairs calcium absorption, causes secondary hyperparathyroidism and increased bone turnover
- Leads to rickets in children and osteomalacia in adults
- Factors affecting vitamin D status include limited sun exposure, sunscreen use, dark skin, obesity, malabsorption disorders, certain medications
Red Blood Cell Transketolase for Thiamin Status
Thiamin's Role in Metabolism
- Thiamin (vitamin B1) is a water-soluble vitamin serving as a coenzyme in key metabolic reactions
- Carbohydrate metabolism
- Neural function
- Deficiency leads to beriberi with neurological, cardiovascular, and gastrointestinal symptoms
- Wernicke-Korsakoff syndrome is a severe deficiency manifestation, primarily in chronic alcoholism
RBC Transketolase Activity Assay
- Red blood cell (RBC) transketolase activity is a functional measure of thiamin status
- Transketolase is a thiamin-dependent enzyme in the pentose phosphate pathway
- Critical for energy production and biosynthesis of nucleic acids and amino acids
- In deficiency, RBC transketolase activity decreases
- Enzyme activity measured with and without added thiamin pyrophosphate (TPP), the active form
- TPP effect (thiamin pyrophosphate stimulation test) measures the percentage increase in RBC transketolase activity after adding TPP
- Increase of >15-25% indicates thiamin deficiency
- More sensitive than direct measurement of thiamin in blood or urine
- Limitations include labor-intensive nature, need for fresh blood samples, potential interference from magnesium deficiency or medications