Date Published: 
Monday, 9 June, 2014

Diagnosing iron deficiency in cardiac patients

Commonalities in the typical symptoms of iron deficiency and heart failure mean clinical presentation is of low diagnostic value in these patients. A thorough screening of blood iron status – including measures of storage, circulating and functional iron – are required to accurately diagnose iron deficiency and should be routine practice in this patient population.

Table 2. The commonalities between symptoms of heart failure (HF) and iron deficiency (ID) and iron deficiency anaemia (IDA)1,2

 

Storage iron: Serum ferritin

The amount of iron sequestered into storage cells can be estimated by measuring serum ferritin levels. A low serum ferritin level is generally used to indicate absolute iron deficiency (<100 µg/L), whereas functional iron deficiency can be present even when ferritin levels are normal (100–300 µg/L). This demonstrates the importance of screening multiple parameters, as ferritin level alone is not sufficient to completely rule out iron deficiency.

Although iron stores are elevated in patients with chronic heart failure compared with healthy individuals (see ‘Why do cardiac patients become iron deficient?’), more detailed analyses reveal that storage iron is progressively depleted as the disease progresses, demonstrating a positive correlation with New York Heart Association (NYHA) functional class (an assessment of symptoms associated with chronic heart failure)3. Although ferritin level is elevated early in the course of chronic heart failure, it gradually diminishes with disease severity. This indicates a direct role for iron disturbance in disease progression, since ferritin level would be expected to continually increase if linked only to inflammation3,4.

Figure 4. Changes in serum ferritin with worsening NYHA class for anaemic and non-anaemic chronic heart failure patients3

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Copyright permission obtained from Okonko et al, 2011.

Circulating iron: Transferrin saturation 

The level of iron circulating in the blood is estimated by measuring transferrin saturation (TSAT). Iron deficiency is indicated when TSAT drops below 20%. In patients with chronic heart failure, circulating iron diminishes as disease worsens, despite the fact that iron stores appear adequate. Although this is true of patients with or without anaemia, the reduction in circulating iron is significantly less marked in non-anaemic patients. Therefore for accurate diagnosis of iron deficiency, TSAT should always be considered in conjunction with other parameters, particularly serum ferritin levels3.

Figure 5. Changes in transferrin saturation with worsening NYHA class for anaemic and non-anaemic chronic heart failure patients3

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Copyright permission obtained from Okonko et al, 2011.

Functional iron – Mean Cell Haemoglobin Concentration 

Iron sequestered by functional proteins is referred to as ‘functional iron’. Haemoglobin accounts for approximately 60% of functional iron and therefore Mean Cell Haemoglobin Concentration (MCHC) is commonly used to estimate functional iron levels. In patients with chronic heart failure, functional iron decreases as disease worsens, despite the fact that iron stores appear adequate. However, patients only become deficient in functional iron once a severe disease state is reached. The MCHC measure is therefore not informative for diagnosing iron deficiency unless considered alongside other iron parameters3.

Figure 6. Changes in mean cell haemoglobin concentration (MCHC) with worsening NYHA class for anaemic and non-anaemic chronic heart failure patients3

Copyright permission obtained from Okonko et al, 2011.

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