What is the best approach to manage anemia in a patient with iron deficiency, negative Cologuard result, and complex medical history, including Type 2 Diabetes Mellitus (T2DM), Proliferative Diabetic Retinopathy (PDR), and Vitamin D deficiency?

Management of Iron Deficiency Anemia with Negative Cologuard

Despite the negative Cologuard result, this patient requires both upper endoscopy (EGD) and colonoscopy to investigate the iron deficiency anemia, as stool-based tests are inadequate for evaluating IDA and the patient has clear laboratory evidence of iron deficiency requiring gastrointestinal evaluation. 1

Diagnostic Confirmation

Your patient has confirmed iron deficiency anemia based on:

• Ferritin 7.1 ng/mL (diagnostic threshold <12 ng/mL confirms iron deficiency) 1
• Hemoglobin 10.7 g/dL (anemia present)
• Iron saturation 24% (77 ÷ 327 = 24%, below the 30% threshold suggesting iron deficiency) 1
• Normal B12 (886 pg/mL) and folate (14.0 ng/mL) exclude other nutritional causes

The serum ferritin is the most powerful test for iron deficiency, and levels below 12 ng/mL are diagnostic even without other confirmatory testing. 1

Why Cologuard is Insufficient

Faecal occult blood testing (including Cologuard) is of no benefit in the investigation of iron deficiency anemia. 1 These tests are designed for colorectal cancer screening in asymptomatic individuals, not for evaluating established IDA. The British Society of Gastroenterology explicitly states that fecal occult blood testing should not be used when investigating IDA. 1

Required Endoscopic Evaluation

Both Upper and Lower GI Investigations Are Mandatory

Upper and lower GI investigations should be considered in all postmenopausal female and all male patients where IDA has been confirmed unless there is a history of significant overt non-GI blood loss. 1 Since patient gender is not specified but they have multiple diabetic complications suggesting they are not a young premenopausal woman, bidirectional endoscopy is indicated.

Upper Endoscopy (EGD) Should Include:

• Visualization of esophagus, stomach, and duodenum (upper GI endoscopy reveals a cause in 30-50% of IDA patients) 1
• Small bowel biopsies during endoscopy to screen for celiac disease (present in 2-3% of IDA patients) 1
• Look for gastric cancer, peptic ulcer disease, angiodysplasia, and erosive disease 1

Colonoscopy Should Be Performed Even If EGD Finds a Lesion

Unless the upper GI endoscopy reveals carcinoma or coeliac disease, all patients should then undergo examination of the lower GI tract as dual pathology occurs in around 10-15% of patients. 1 This means:

• Finding esophagitis, erosions, or peptic ulcer on EGD should NOT deter colonoscopy 1
• Colonoscopy has advantages over CT colonography for investigating IDA, though either is acceptable and both are preferable to barium enema 1
• Colonoscopy allows visualization of angiodysplasia and biopsy capability 1

Clinical Reasoning for This Patient

Urgency Considerations

The lower the hemoglobin, the more likely there is to be serious underlying pathology and the more urgent is the need for investigation. 1 With hemoglobin of 10.7 g/dL, this warrants reasonably prompt evaluation.

Risk Factors Present

This patient has several factors increasing concern:

• Type 2 diabetes (associated with increased GI malignancy risk)
• Multiple comorbidities suggesting older age
• Diabetic nephropathy (though this can cause anemia, the ferritin of 7.1 confirms true iron deficiency, not anemia of chronic disease) 1

Common Pitfalls to Avoid

• Do not accept the negative Cologuard as sufficient investigation 1
• Do not stop at finding an upper GI lesion without also investigating the colon (dual pathology occurs in 10-15% of cases) 1
• Do not assume diabetic nephropathy explains the anemia when ferritin is this low 1
• Do not delay investigation based on the complex medical history; serious pathology like GI malignancy must be excluded 1

Concurrent Iron Supplementation

While arranging endoscopy, all patients should have iron supplementation both to correct anaemia and replenish body stores. 1

• Ferrous sulfate 200 mg three times daily is the standard oral therapy 1
• Each 324 mg tablet of ferrous sulfate contains 65 mg elemental iron 2
• Iron supplementation should be continued for three months after correction of anaemia to replenish iron stores 1
• Parenteral iron can be used when oral preparations are not tolerated 1

Further Investigation Scenarios

Further direct visualization of the small bowel is not necessary unless there are symptoms suggestive of small bowel disease, or if the haemoglobin cannot be restored or maintained with iron therapy. 1 This means capsule endoscopy or enteroscopy should only be considered if:

• Both EGD and colonoscopy are normal AND
• The patient becomes transfusion-dependent OR
• Hemoglobin cannot be maintained with oral iron 1