Does low ferritin in adult men indicate depleted iron stores and possible occult blood loss?

Clinical evidence

• High diagnostic specificity: In adult men, a serum ferritin cutoff of $\le$30 $\mu$g/L demonstrates an exceptionally high specificity of 98% to 99% (approaching 100% at $\le$15 $\mu$g/L) for depleted bone marrow iron stores, the clinical gold standard.
• Limitations in sensitivity: Because ferritin is an acute-phase reactant, concurrent inflammation or chronic disease can artificially elevate levels. In these contexts, higher diagnostic thresholds ($<$70 to $<$100 $\mu$g/L) are utilized, as conventional cutoffs have a modest sensitivity of approximately 35% in men.

Mechanistic explanations

• Pathology of depletion: Chronic occult gastrointestinal (GI) blood loss—secondary to peptic ulcers, inflammatory bowel disease, or colorectal malignancies—is the primary driver that drains systemic iron stores in men. Low ferritin serves as the earliest laboratory indicator of this blood loss, often manifesting before the onset of overt anemia.
• Fluctuations in serum iron: Serum iron is highly labile and fluctuates daily. Consequently, normal or even elevated serum iron levels frequently coexist with depleted iron stores (iron deficiency without anemia). Normal serum iron does not rule out underlying iron depletion or active, intermittent hemorrhage.

Bottom line

• Low serum ferritin ($\le$30 $\mu$g/L) is a highly specific indicator of depleted iron stores in adult men and warrants a proactive diagnostic workup (such as bidirectional endoscopy) for occult gastrointestinal blood loss, even when serum iron levels appear entirely normal.