What blood tests can be requested to check for deficiencies in a patient with mouth ulcers and pale fingernails?

Blood Tests for Mouth Ulcers and Pale Fingernails in a 16-Year-Old

Request a complete blood count (CBC) with ferritin levels as the essential first-line tests, followed by vitamin B12 and folate levels if initial results suggest deficiency. 1, 2

Essential First-Line Tests

Complete Blood Count (CBC)

• CBC is the foundational test that provides hemoglobin levels, red blood cell indices (MCV, MCH, MCHC), white blood cell count, and platelet count 1, 2
• Hemoglobin <12 g/dL in females or <13 g/dL in males defines anemia, which commonly presents with pale fingernails 2
• Mean Corpuscular Volume (MCV) helps classify the type of anemia: <80 fL indicates microcytic (iron deficiency), 80-100 fL normocytic, >100 fL macrocytic (B12/folate deficiency) 2
• Red Cell Distribution Width (RDW) is particularly useful as elevated RDW suggests coexisting deficiencies 2

Iron Studies

• Serum ferritin is the most sensitive marker for iron stores and should be checked in all patients with chronic mouth ulcers and suspected anemia 1, 2
• Ferritin <30 μg/L indicates iron deficiency in the absence of inflammation 1, 2
• In the presence of inflammation (check C-reactive protein), ferritin up to 100 μg/L may still indicate iron deficiency 1, 2
• Transferrin saturation <20% indicates functional or absolute iron deficiency 1, 2

Second-Line Tests Based on Initial Results

If Macrocytic Anemia (High MCV)

• Vitamin B12 and folate levels should be measured when MCV is elevated, as deficiencies cause mouth ulcers and anemia 1
• These deficiencies are less common but important causes of both oral ulceration and anemia 1

If Microcytic Anemia (Low MCV)

• Iron deficiency is the most common cause of microcytic anemia with mouth ulcers 1
• If ferritin is borderline (30-100 μg/L), check serum iron and total iron binding capacity to clarify iron status 1

Additional Considerations

• C-reactive protein (CRP) should be measured alongside ferritin to assess for inflammation, which affects ferritin interpretation 2
• Reticulocyte count helps distinguish between production defects (low reticulocytes) and blood loss/hemolysis (high reticulocytes) 2

Important Clinical Pitfalls

Avoid These Common Errors

• Do not rely solely on MCV for classification, as coexisting deficiencies (e.g., iron + B12) can normalize MCV while RDW remains elevated 2
• Do not misinterpret ferritin without considering inflammatory status, as ferritin is an acute-phase protein that rises with inflammation even in iron deficiency 1, 2
• Do not overlook tissue transglutaminase (TTG) antibodies if unexplained iron deficiency is found, as celiac disease can cause both malabsorption and mouth ulcers 1

Diagnostic Algorithm Summary

1. Start with CBC and ferritin in all cases of mouth ulcers with pale fingernails 1, 2
2. Add CRP to interpret ferritin accurately 2
3. If MCV is low: Confirm iron deficiency with transferrin saturation and consider TTG antibodies 1, 2
4. If MCV is high: Check vitamin B12 and folate levels 1, 2
5. If MCV is normal but RDW is high: Consider mixed deficiency and check both iron studies and B12/folate 2

Why This Approach Works

The combination of mouth ulcers and pale fingernails strongly suggests nutritional deficiency anemia 1. Iron deficiency is the most common cause and responds rapidly to treatment, with some patients experiencing complete resolution of symptoms shortly after starting iron replacement 1. The systematic approach using CBC with indices and targeted follow-up tests based on MCV provides cost-effective diagnosis while avoiding unnecessary testing 2, 3.