Summary

AGA 2020 guideline on the gastrointestinal evaluation of iron deficiency anemia (IDA), developed using GRADE. Covers ferritin cutoff for diagnosis, endoscopic evaluation strategy by sex/menopausal status, and workup for H. pylori, celiac disease, atrophic gastritis, and small-bowel sources after negative bidirectional endoscopy. Does not address refractory/recurrent IDA, obscure GI bleeding, or iron replacement regimens.

Key Recommendations

Use ferritin cutoff of 45 ng/mL (not 15 ng/mL) to diagnose iron deficiency in patients with anemia (strong, high quality).
In patients with chronic inflammation or CKD, add CRP, transferrin saturation, or soluble transferrin receptor to ferritin to diagnose iron deficiency.
Perform bidirectional endoscopy (EGD + colonoscopy) in asymptomatic postmenopausal women and men with IDA, done at the same setting (strong, moderate quality).
Suggest bidirectional endoscopy over iron replacement alone in asymptomatic premenopausal women with IDA, with shared decision-making given low malignancy yield (conditional, moderate quality).
After negative bidirectional endoscopy without an identified etiology, perform noninvasive H. pylori testing (stool antigen, urea breath, or serology) and treat if positive (conditional, low quality).
Do not perform routine gastric biopsies to diagnose autoimmune atrophic gastritis in IDA patients (conditional, very low quality).
In asymptomatic adults with IDA and plausible celiac disease, obtain celiac serology first and pursue small-bowel biopsy only if positive, rather than routine duodenal biopsy (conditional, very low quality).
Consider routine duodenal biopsies if celiac prevalence in the population is >5%, if duodenum appears abnormal endoscopically, or in higher-risk patients (family history, type 1 DM, symptoms).
In uncomplicated asymptomatic IDA with negative bidirectional endoscopy, trial iron supplementation rather than routine video capsule endoscopy (conditional, very low quality).
Start oral iron as initial therapy in most patients; reserve IV iron for malabsorption, prior gastric surgery, IBD, CKD, or blood loss exceeding oral repletion capacity.
Reassess for nonadherence, malabsorption, ongoing blood loss, or missed celiac disease if hemoglobin does not improve within ~1 month of oral iron.

Thresholds & Doses

Ferritin <45 ng/mL: diagnostic threshold for iron deficiency in anemic patients (preferred over <15 ng/mL).
Anemia definition: hemoglobin <13 g/dL in men, <12 g/dL in nonpregnant women.
Diagnostic yield in postmenopausal women/men with IDA: lower GI malignancy 8.9% (95% CI 8.3–9.5%), upper GI malignancy 2.0% (95% CI 1.7–2.3%).
Diagnostic yield in premenopausal women with IDA: lower GI malignancy 0.9% (95% CI 0.3–1.9%), upper GI malignancy 0.2% (95% CI 0–0.9%).
Celiac disease prevalence threshold favoring routine duodenal biopsy over serology-first: >5%.
Historical oral iron dose: 150–200 mg elemental iron daily; lower or alternate-day dosing may improve tolerability/absorption.
Expected hemoglobin response to oral iron: within ~1 month.

Citations

Table 3 (Executive Summary of Recommendations) — all 7 recommendations and strength/quality grades.
Recommendation 1 (ferritin cutoff) — 45 ng/mL over 15 ng/mL, strong/high quality.
Recommendation 2 (bidirectional endoscopy in postmenopausal women and men) — strong/moderate quality, with pooled malignancy yields.
Recommendation 3 (premenopausal women) — conditional recommendation for bidirectional endoscopy with shared decision-making.
Recommendations 4–5 (H. pylori testing and against routine gastric biopsies for atrophic gastritis) — post-endoscopy workup.
Recommendation 6 (celiac serology first vs routine small-bowel biopsy) — including >5% prevalence caveat.
Recommendation 7 (iron trial over video capsule endoscopy after negative bidirectional endoscopy).
Section ‘How should iron supplementation be managed?’ — oral vs IV iron, dosing, response timing.