How to interpret a blood test for iron deficiency anemia?

From the Guidelines

To interpret blood tests for iron deficiency, look for low serum ferritin (below 15 μg/L), which is a specific indicator of depleted iron stores, as recommended by the Centers for Disease Control and Prevention 1. When interpreting blood tests for iron deficiency, several key markers should be considered, including:

• Low serum ferritin (below 15 μg/L) as the most specific indicator of depleted iron stores 1
• Low serum iron (typically below 60 μg/dL)
• Elevated total iron binding capacity (TIBC) (often above 400 μg/dL)
• Low transferrin saturation (below 16%) A complete blood count may show low hemoglobin (below 13.5 g/dL for men and 12.0 g/dL for women) and small, pale red blood cells (microcytic, hypochromic anemia) in advanced deficiency. It is essential to investigate the underlying cause of iron deficiency, as it may result from blood loss, poor absorption, or increased requirements, and follow-up testing is recommended after 2-3 months of treatment to monitor improvement in iron levels and hemoglobin, as suggested by the British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults 1. In cases where inflammation is present, the interpretation of iron deficiency may be complicated, and other markers such as C-reactive protein or measures of iron status such as total iron binding capacity should be considered, as noted in the British Obesity and Metabolic Surgery Society guidelines on perioperative and postoperative biochemical monitoring and micronutrient replacement for patients undergoing bariatric surgery-2020 update 1. The most recent and highest quality study, the British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults 1, recommends that iron deficiency should be confirmed by iron studies prior to investigation, and a good response to iron therapy is highly suggestive of absolute iron deficiency.

From the Research

Interpreting Blood Tests for Iron Deficiency

To interpret blood tests for iron deficiency, several factors and measurements are considered, including:

• Serum ferritin levels: Low serum ferritin (typically <30 ng/mL) is a key indicator of iron deficiency in individuals without inflammatory conditions 2.
• Transferrin saturation: This measurement, calculated by dividing serum iron by total iron binding capacity (TIBC) and multiplying by 100, can also be used to diagnose iron deficiency, particularly in patients with chronic inflammatory diseases 3.
• Total iron binding capacity (TIBC): TIBC measurement alone can outperform iron and saturation indices in predicting iron deficiency 4.

Diagnostic Criteria

The diagnostic criteria for iron deficiency include:

• Low serum ferritin levels (<30 ng/mL) in individuals without inflammatory conditions 2.
• Transferrin saturation less than 20% 2.
• TIBC measurement can be used as an alternative or in addition to ferritin and transferrin saturation 4, 3.

Limitations of Certain Measurements

Some measurements, such as serum iron and TIBC, may not provide additional information in the diagnosis of iron deficiency anemia if serum ferritin is available 5.

• Serum iron and TIBC have lower sensitivity and specificity compared to ferritin and transferrin saturation 5.
• Ferritin shows poor correlation with iron, TIBC, and transferrin saturation, highlighting the importance of using multiple measurements for accurate diagnosis 5.