Nutrient Deficiency Evaluation
Nutrient deficiency evaluation should be targeted to specific risk factors and symptoms rather than applied as a broad screen, per AAFP guidance and Endocrine Society and USPSTF/Choosing Wisely recommendations.
Symptoms
Vitamin B12 deficiency can cause fatigue, numbness/tingling, and cognitive changes; vitamin D deficiency is often asymptomatic or causes vague fatigue and bone pain; iron deficiency causes fatigue and pallor; magnesium deficiency can cause muscle cramps and, when severe, heart rhythm changes.
Causes and risk
Restrictive diets (vegan, ketogenic, gluten-free), malabsorption conditions, certain medications, heavy menstrual bleeding, and reduced intake with aging all raise risk for specific deficiencies.
How it is evaluated
Clinically useful, validated tests include total B12 (with reflex methylmalonic acid for borderline results), 25-OH vitamin D, and ferritin with transferrin saturation for iron status -- testing is best targeted at people with a real risk factor or symptom rather than done as a universal panel, per AAFP guidance. Hair mineral analysis has been shown to have over tenfold variability between commercial labs and conflicting results, per a JAMA assessment of commercial labs, and is not a validated diagnostic tool. Serum magnesium reflects less than 1% of total body magnesium stores, so a normal level does not rule out deficiency.
Treatment
Oral supplementation is first-line for most deficiencies once confirmed, with the specific dose and form depending on the nutrient and severity; injectable or IV forms are reserved for severe deficiency, malabsorption, or neurologic involvement.
When to seek care
Severe muscle cramps, an irregular heartbeat, or seizures can signal dangerous magnesium or electrolyte imbalance and need emergency evaluation. Advancing numbness, difficulty walking, or confusion in someone with B12 deficiency also warrants prompt medical attention, since untreated neurologic damage can become permanent.