What tests are included in iron studies?

Iron Studies Components

Iron studies typically include serum ferritin, transferrin saturation, serum iron, and total iron binding capacity (TIBC). These tests collectively provide a comprehensive assessment of iron status in the body 1.

Core Components of Iron Studies

Primary Tests

• Serum Ferritin: The single most useful marker of iron deficiency 1

  • Reflects iron stores in the body
  • Low levels (<15-30 μg/L) indicate depleted iron stores 1
  • Can be falsely elevated in inflammatory conditions as it's an acute phase reactant 1

• Transferrin Saturation:

  • Calculated as (serum iron ÷ TIBC) × 100
  • Values <20% suggest iron deficiency 1
  • Values >55% may indicate iron overload 1

• Serum Iron:

  • Measures circulating iron bound to transferrin
  • Subject to diurnal variation (higher in morning)
  • Less reliable as a standalone test 1

• Total Iron Binding Capacity (TIBC) or Transferrin:

  • Reflects the blood's capacity to bind iron
  • Elevated in iron deficiency
  • May outperform serum iron alone in predicting iron deficiency 2

Clinical Interpretation

Iron Deficiency Pattern

• Low serum ferritin (<30 μg/L)
• Low transferrin saturation (<20%)
• Low serum iron
• Elevated TIBC

Iron Overload Pattern

• Elevated serum ferritin (>200 ng/mL in women, >300 ng/mL in men) 1
• High transferrin saturation (>55%)
• Elevated serum iron
• Normal or low TIBC

Important Considerations

1. Timing of Collection: Blood samples for transferrin saturation should be taken in the morning, though fasting is not necessary 1.

2. Confounding Factors:

   • Ferritin is an acute phase reactant and may be falsely elevated in:
     • Inflammatory conditions
     • Liver disease
     • Malignancy
     • Metabolic syndrome 1

3. Diagnostic Accuracy:

   • Serum ferritin has superior diagnostic value compared to iron and TIBC for detecting iron deficiency 3
   • However, in certain clinical scenarios, a combination of tests provides better diagnostic accuracy

4. Additional Tests: In some cases, other markers may be included:

   • Red cell indices (MCV, MCH) - can indicate microcytosis and hypochromia in iron deficiency 1
   • Erythrocyte protoporphyrin - detects early changes in iron status 1
   • Serum transferrin receptor - may help differentiate between iron deficiency and anemia of chronic disease

Clinical Application

When evaluating for iron deficiency anemia, a good response to iron therapy (Hb rise ≥10 g/L within 2 weeks) is highly suggestive of absolute iron deficiency, even if iron studies are equivocal 1.

For suspected iron overload conditions like hemochromatosis, transferrin saturation >55% and elevated ferritin are key diagnostic indicators 1.

Remember that no single test is accepted for definitively diagnosing iron deficiency or iron overload, and results should be interpreted in the clinical context 1.