Revised Ferritin Thresholds for Iron‑Deficiency Diagnosis in the UK

Diagnostic Accuracy of Low Ferritin Levels

Ferritin < 15 µg/L is highly specific (specificity ≈ 0.99) for iron deficiency and indicates absent iron stores, making it the most reliable threshold for confirming iron deficiency when inflammation is absent. British Society of Gastroenterology 1, 2, 3, 4, 5
Sensitivity of ferritin < 15 µg/L is limited (≈ 59%); therefore, using this cut‑off alone misses about 41% of iron‑deficient patients. British Society of Gastroenterology 6

Ferritin 15–30 µg/L reflects low body iron stores and is regarded as the lower limit of normal by most UK laboratories; the British Society of Gastroenterology endorses ferritin < 30 µg/L as indicative of low iron stores. British Society of Gastroenterology 1, 2, 7, 3
A ferritin cut‑off of 45 µg/L provides optimal diagnostic performance (sensitivity ≈ 85%, specificity ≈ 92%) and is recommended as the practical threshold for investigating iron deficiency, especially in patients with chronic inflammation or anaemia. British Society of Gastroenterology 1, 2, 6
Ferritin values below 45 µg/L should trigger further evaluation for iron deficiency when chronic inflammation or anaemia is present. British Society of Gastroenterology 1, 2, 4

Ferritin is an acute‑phase protein that rises during inflammation, which can mask underlying iron deficiency. British Society of Gastroenterology 2, 3, 5
C‑reactive protein (CRP) should be measured concurrently with ferritin to help differentiate inflammation‑related ferritin elevation from true iron repletion. British Society of Gastroenterology 1

Ferritin > 150 µg/L is unlikely to occur in absolute iron deficiency, even in severe inflammatory states; this value is the evidence‑based upper exclusion threshold endorsed by the British Society of Gastroenterology. British Society of Gastroenterology 1, 2, 3, 4, 7

Soluble transferrin receptor (sTfR) is not affected by inflammation and offers superior discrimination of iron deficiency, although it is not routinely available in most UK hospitals. British Society of Gastroenterology 1, 3, 5
The sTfR / log₁₀ ferritin ratio may outperform either marker alone for diagnosing iron deficiency in chronic disease. British Society of Gastroenterology 1, 5
Mean cell hemoglobin (MCH) may be more sensitive than mean corpuscular volume (MCV) for detecting iron deficiency. British Society of Gastroenterology 1, 3

Do not rely exclusively on ferritin < 15 µg/L for diagnosis, as this approach misses roughly 41% of iron‑deficient individuals. British Society of Gastroenterology 6
Do not consider ferritin values between 30–100 µg/L as normal without assessing inflammatory markers such as CRP. British Society of Gastroenterology 1, 2
Do not use a ferritin cut‑off of 100 µg/L as the upper exclusion limit; the correct upper limit is 150 µg/L. British Society of Gastroenterology 1, 2, 3