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Perth Haematology :: Dr Steven Ward

Iron Studies  : Assessment of iron status

 

 

Iron Studies pdf file

 

ASSESSMENT OF IRON STORES

Interpretation of iron studies

 4 tests are commonly performed as “iron studies”:

 

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Serum iron (Fe) is virtually useless in assessing iron stores. It merely reflects how much iron is circulating; and has no bearing on stored iron (in the liver, marrow, etc). Serum iron levels vary considerably even in normal healthy people. The levels vary during the day, depend on recent food intake, intercurrent illness and probably other factors.

 

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Transferrin (TF) is the transport molecule, which moves iron around the body. Transferrin levels rise when iron deficient (looking for iron), or with pregnancy and oestrogen therapy, low levels are found in “chronic disease”

 

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Transferrin Saturation (TF%) is a calculated value using the transferrin and serum iron. It is obvious that this value depends on the very labile and variable serum iron level, and hence is often of limited true utility.

 

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Ferritin is the “store room” for iron. It is usually present in the blood in proportion to the tissue levels, and is the best test available routinely to estimate body iron stores. Ferritin is responsible for storing iron, and the levels rise and fall depending on the amount for iron present. Low levels indicate iron deficiency. However high levels do not always indicate iron overload. Ferritin is produced by the liver and is also an “acute phase protein”. It is produced at times of inflammation and infection, without regard to the iron status. Therefore high ferritin may be due to infection/inflammation or iron overload.

 

 

Pitfalls of using transferrin saturation

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Transferrin saturation (TF%) is often used in the determination of iron status, as no single test is ideal.

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There are, however, major problems with TF% as it is a calculated value based on serum iron and transferrin levels. Both serum iron and to a lesser degree transferrin are labile and influenced by many factors.

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Using a calculated value from two labile measurements will lead to further variation in results.

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 I have found TF% to be of little value in itself, particularly when the serum iron is a t extremes (low or high); skewing the TF%.

 

Analyte

Units

Reference Range

Serum Iron

umol/L

11-30

Transferrin

umol/L

20-45

Transferrin saturation [CALCULATED]

%

15-55%

Ferritin

ug/L

15-200 F  30 -400 M

 

TF% = Serum iron / (Transferrin X 2) both in umol/L

 

EXAMPLES

 

Iron

TF

TF%

Ferritin

Interpretation

5

48

5%

7

Iron deficiency. Low ferritin; low Fe, High TF; Low TF% - Classical

36

28

64%

790

Iron overload likely; high Ferr, high iron, N TF; Hi TF%

6

28

11%

250

Likely normal iron status; normal ferritin; normal TF; Low iron leads to low TF%. Liable iron

4

15
13%
460
Low iron; Lowish TF; low %; High Ferritin - Chronic Disease
6
15
20%
460
Same pt as above:  Fe 2 higher (still lo)  Lowish TF; Sat now N; Hi ferr
5
34
7%
180
Normal ferr; normal TF - likely N; lo Fe gives low TF%- FE labile
         
33
28
78%
147
Hi iron; lower but N TF; Sat Hi ?? Iron o/load' but ferr N. All due to calculation.
30
28
53%
147
If above pt has iron of 30 the satn isn't so markedly hi at 53%
         

 LOW

NORMAL

HIGH