What are the appropriate next steps for a vegetarian patient with normal complete blood count, comprehensive metabolic panel, and thyroid stimulating hormone levels, slightly low ferritin, and pruritus on the face, shins, and back, who is not taking vitamin B12 supplements?

Check B12 Level Immediately and Address Iron Deficiency

Your next step is to measure serum vitamin B12 (or active B12/holotranscobalamin) immediately, as this vegetarian patient without supplementation is at high risk for B12 deficiency, which can cause neurological complications even with normal CBC. 1 Simultaneously, initiate iron supplementation for the low ferritin.

Why B12 Testing is Critical

This patient has two major risk factors for B12 deficiency:

• Vegetarian diet without B12 supplementation 1
• Research shows 10-40% of vegetarians have frank B12 deficiency despite normal hemoglobin 2, 3

The normal CBC is falsely reassuring—B12 deficiency can present with neurological symptoms (including paresthesias that could manifest as pruritus) before macrocytic anemia develops 1. When iron deficiency coexists with B12 deficiency, the microcytosis from iron deficiency can mask the macrocytosis from B12 deficiency, creating a deceptively normal MCV 4.

B12 Testing Approach

• Order either total B12 (serum cobalamin) or active B12 (holotranscobalamin) 1
• Active B12 is more accurate but costs £18 vs £2 for total B12 1
• Either test is acceptable for initial screening 1
• If result is indeterminate (total B12 200-350 pmol/L), consider methylmalonic acid (MMA) for confirmation 1

Iron Deficiency Management

With slightly low ferritin and normal CBC, this represents non-anemic iron deficiency (NAID). While vegetarians commonly have depleted iron stores (ferritin <12 μg/L in 12-79% of female vegetarians and 1.7-29% of males) 5, the low ferritin warrants treatment:

• Start oral iron supplementation (ferrous sulfate 325mg daily or equivalent)
• Ferritin <30 μg/L indicates low body iron stores 6
• GI investigation is not indicated for NAID in the absence of other concerning features 6
• Vegetarian diets provide adequate iron quantity but poor bioavailability (all non-heme iron) 3

Addressing the Pruritus

The itching requires a separate diagnostic approach:

Most likely causes to evaluate:

• Xerosis (dry skin) - most common cause of generalized pruritus with normal labs
• B12 deficiency - can cause neurological symptoms including paresthesias that may present as itching
• Dermatological examination - look for primary skin lesions (eczema, psoriasis, dermatitis)

Less likely given normal labs:

• Thyroid dysfunction (TSH normal)
• Renal dysfunction (CMP normal)
• Hepatic cholestasis (CMP normal)

Pruritus Workup

If B12 is normal and skin examination unrevealing:

• Consider bile acids if any subtle liver enzyme elevation
• Trial of emollients for xerosis
• Reassess after iron/B12 repletion (symptoms may improve)

Common Pitfalls to Avoid

1. Don't assume normal CBC rules out B12 deficiency - neurological manifestations can precede hematological changes 1

2. Don't miss coexisting deficiencies - iron deficiency can mask B12 deficiency on blood count 4

3. Don't over-investigate the low ferritin - in a vegetarian without anemia, this is expected and doesn't require endoscopy 6, 5

4. Don't delay B12 supplementation if deficiency confirmed - neurological damage can become irreversible 1

Follow-Up Plan

• Recheck ferritin in 3 months after iron supplementation
• If B12 deficient: Start replacement therapy (oral or IM depending on level and symptoms) 1
• Dietary counseling: Recommend B12-fortified foods or supplements for long-term prevention 1
• Reassess pruritus after 4-6 weeks of nutritional repletion

The combination of vegetarian diet, no B12 supplementation, and low ferritin creates a high-risk scenario for multiple nutritional deficiencies that can have serious neurological consequences if left untreated.