From the Guidelines
Serum ferritin < 15 µg/L is the most suggestive test for iron deficiency anemia in a patient presenting with fatigue, weakness, and conjunctival pallor. This is because a low serum ferritin level is highly specific for iron deficiency and represents depleted iron stores in the body 1. While other tests like hemoglobin, hematocrit, mean corpuscular volume (MCV), and peripheral blood smear can indicate anemia and suggest iron deficiency, ferritin provides the most direct assessment of iron stores.
Additional useful tests include serum iron, total iron binding capacity (TIBC), and transferrin saturation, which are often abnormal in iron deficiency anemia (low serum iron, high TIBC, and low transferrin saturation) 1. However, it's essential to consider the patient's inflammatory status, as ferritin is an acute phase reactant and may be falsely elevated in inflammatory conditions, potentially masking iron deficiency in these situations 1.
Some key points to consider when interpreting ferritin levels include:
- A ferritin level < 15 µg/L indicates absolute iron deficiency 1
- A ferritin level < 30 µg/L is generally indicative of low body iron stores 1
- In the presence of inflammation, a ferritin level < 100 µg/L may indicate iron deficiency 1
- A ferritin threshold value of < 45 ng/mL has a sensitivity for iron deficiency of 85% and a specificity of 92% 1
Overall, serum ferritin is a valuable test for diagnosing iron deficiency anemia, but it should be interpreted in the context of the patient's clinical presentation and other laboratory results.
From the Research
Diagnostic Tests for Iron Deficiency Anemia
The patient's symptoms of fatigue, weakness, and conjunctival pallor suggest iron deficiency anemia. To confirm the diagnosis, several tests can be considered:
- Serum ferritin level: This is the most sensitive and specific test for iron deficiency anemia 2, 3.
- Mean corpuscular volume (MCV): This test measures the average size of red blood cells. Iron deficiency anemia is typically characterized by a microcytic anemia (MCV < 80 fL) 2.
- Total iron-binding capacity (TIBC): This test measures the amount of transferrin available to bind to iron. In iron deficiency anemia, TIBC is typically increased 2.
- Basophilic stippling: This is a morphological feature of red blood cells that can be seen in iron deficiency anemia, but it is not a specific or sensitive test 2.
Most Suggestive Test
Based on the evidence, the most suggestive test for iron deficiency anemia is a serum ferritin level < 15 µg/L 4, 2, 3. A low serum ferritin level indicates depleted iron stores, which is a hallmark of iron deficiency anemia.
Rationale
The rationale for choosing serum ferritin level as the most suggestive test is based on its high sensitivity and specificity for iron deficiency anemia 2, 3. Additionally, serum ferritin level is a direct measure of iron stores, making it a more accurate test than other indirect measures such as MCV or TIBC 4, 2.
Supporting Evidence
Studies have shown that serum ferritin level is a reliable test for iron deficiency anemia, with a sensitivity and specificity of 79% and 98%, respectively 3. Additionally, a serum ferritin level < 15 µg/L has been shown to be a specific indicator of iron deficiency anemia 4, 2.