Total iron contain in 1 mg Hb?

Appeared in: BSF Staff Nurse - 2021

Explanation

The question contains a likely unit error, intending to ask for the iron content in 1 gram of hemoglobin, not 1 milligram.
Standard physiological references state that iron constitutes about 0.334% to 0.34% of hemoglobin by weight.
Calculating this for 1 gram (1000 mg) of hemoglobin: 1000 mg * 0.00334 = 3.34 mg, or 1000 mg * 0.0034 = 3.4 mg.
Among the given choices, 3.45 mg is the closest and most accepted value in this context, accounting for slight variations in measurement and rounding in different sources.

Option B: This value is too low and does not correspond to the known percentage of iron in the hemoglobin molecule.
Option C: This value is incorrect and significantly lower than the established physiological constant for iron content in hemoglobin.
Option D: This value is too high. While iron is essential, it makes up a very small fraction of the hemoglobin molecule's total mass.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Calculation of iron content in hemoglobin as background academic context rather than a clinical decision trigger.
Knowing the iron content of hemoglobin is crucial for calculating a patient's total iron stores and assessing the impact of blood loss.
For example, a nurse can estimate the amount of iron replacement a patient needs after a hemorrhage by calculating the volume of blood lost and using the constant of ~3.4 mg of iron per gram of hemoglobin.
This knowledge is fundamental in managing iron deficiency anemia, where treatment aims to replenish both hemoglobin levels and the body's iron reserves (ferritin).

How to Approach the Question

First, analyze the question and options. Notice the discrepancy: the question asks for content in '1 mg' but the options are large 'mg' values. This suggests a typo in the question, which likely meant '1 gram'.
Recall or look up the physiological constant for the percentage of iron in hemoglobin by weight. This is approximately 0.34%.
Perform the calculation: 1 gram of Hb is 1000 mg. The iron content is 1000 mg * (0.34 / 100) = 3.4 mg.
Compare the calculated value (3.4 mg) with the given options.
Select the closest option, which is 3.45 mg. In exams, physiological constants can have slight variations, so choosing the nearest answer is the correct strategy.

Concept Tested & Keywords

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E6 Physiology Essentials Sembulingam 10e Part 1 p. 96-98

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