Weakness plus brittle nails in a 36-year-old woman commonly suggests iron deficiency, with or without anemia, particularly if she has heavy or prolonged menstrual bleeding. It should be confirmed rather than treating blindly, because thyroid disease, pregnancy, vitamin deficiencies, chronic illness, and nail conditions can also contribute.
Assess first
- Menstrual history: heavy bleeding, clots, periods lasting more than 7 days, frequent periods
- Diet, recent pregnancy/breastfeeding, weight loss, gastrointestinal symptoms, medications
- Examine for pallor, spoon-shaped nails, thyroid signs, fungal nail infection
Initial tests
- CBC with indices: Hb, MCV, MCH, RDW
- Serum ferritin, preferably with transferrin saturation/iron studies
- TSH
- Urine/serum pregnancy test if relevant
- Consider B12, folate, vitamin D, zinc, glucose, renal/liver tests based on clinical findings.
Ferritin is the key initial test for iron deficiency. The AGA advises a ferritin threshold of
<45 ng/mL in a patient with anemia when diagnosing iron deficiency; inflammation can make ferritin misleadingly normal or high. See the
AGA guidance.
If iron deficiency is confirmed and she is not pregnant and has no contraindication:
- A practical regimen is one tablet of ferrous sulfate, ferrous fumarate, or ferrous gluconate once daily. If nausea, constipation, or abdominal pain occur, use it on alternate days or after food. The 2025 NHS primary-care guide supports daily single-tablet therapy and alternate-day use if not tolerated (ferritin and oral-iron guide).
- Take away from tea, coffee, calcium, and antacids by about 2 hours. Vitamin C or citrus may help absorption.
- Recheck CBC in about 4 weeks. Continue iron for roughly 3 months after hemoglobin normalizes to restore stores.
- Identify and treat the cause, especially heavy menstrual bleeding. Iron-deficiency anemia requires investigation for the source of loss, not just supplementation. Textbook of Family Medicine 9e, Key Points.
Brittle or spoon-shaped nails can occur in established iron deficiency. Fitzpatrick's Dermatology, Iron Deficiency.
Refer or urgently assess if Hb is very low, there is syncope, chest pain, shortness of breath at rest, tachycardia, black stools, unexplained weight loss, severe menstrual bleeding, pregnancy, or no improvement after 4 to 6 weeks of correctly taken iron. If menses are not heavy, evaluate for gastrointestinal blood loss, malabsorption, or other causes rather than assuming dietary deficiency.