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A colonoscopy is usually advised as there can be polyps in the intestines (benign growths) which can bleed intermittently and can cause anemia. Colonoscopy can be done with a low hemoglobin (but the risk is increased as sedation or anesthesia given during the procedure may cause sudden breathing issue or low oxygenation).
But she would require other investigations too apart from colonoscopy. Ferritin is a blood test which evaluates for the total iron available in the body. Serum ferritin is the most useful test for diagnosing iron-deficiency anemia. Low serum ferritin (less than 12 ng/mL) is highly specific for iron-deficiency anemia. Please read this resource;
The most common causes of anemia are;
1) iron deficiency (with or without blood loss),
2) chronic disease/inflammation
3) chronic kidney disease
4) deficiencies of folate or vitamin B-12,
5) diseases of the bone marrow
6) hypothyroidism, hypersplenism, and hemolytic anemia
So investigations entail;
1) Complete blood count (CBC)
2) Peripheral blood film
3) Vitamin B-12
5) Reticulocyte count
7) Thyroid-stimulating hormone
8) Serum creatinine and estimated glomerular filtration rate
9) Serum ferritin
10) Serum iron
11) Total iron-binding capacity
So these investigations also need to be done for the exact assessment and long term management.
Please feel free for your follow up questions.
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