Serum iron
Serum iron is the iron carried in blood on transferrin. US survey laboratory manuals print adult ranges from 59 to 158 µg/dL in men and 37 to 145 in women, with wider ranges in older manuals. The result varies about 28% between draws and rises after meals and iron tablets. One cohort linked both ends to more deaths.
- Status
- Part of an iron panel, ordered by a clinician and also sold direct to consumers by some US laboratories. FDA classifies iron (non-heme) test systems as class I devices exempt from premarket notification [1].
- Measures
- The concentration of iron in serum, nearly all of it carried on the transport protein transferrin [2].
- Also called
- iron, serum iron, Fe, serum Fe, iron serum, iron total, total iron, iron level, blood iron, iron blood test
- Tested for
- iron deficiency, anemia workup, fatigue, iron overload, hemochromatosis screening, checking an iron supplement, iron testing in kidney disease
Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on
Linked in research3
- LimitedLimited evidence: one Taiwanese cohort linked both low and high serum iron to more deaths over 19 years, 27% and 37% more than the middle group.
- LimitedLimited evidence: one genetic study found higher serum iron went with slightly less coronary artery disease, an odds ratio of 0.94 per standard deviation.
- LimitedLimited evidence: one genetic study found higher serum iron went with slightly more stroke, an odds ratio of 1.07 per standard deviation.
Reported risks0
No risks sourced yet.
Reference ranges
Each range is the one its source published, in µg/dL. Also reported in µmol/L. Where sources differ, each is shown.
US national survey laboratory procedure manual, 2017 to 2018, men
Adult men, as the reference range printed for the serum assay · [2]
| Range | What the source calls it |
|---|---|
| below 59 µg/dL | No name given |
| 59 to 158 µg/dL | "reference range" |
| above 158 µg/dL | No name given |
The reference range listed in the laboratory manual for the method used in the 2017 to 2018 US National Health and Nutrition Examination Survey (Roche Cobas 6000, FerroZine method), with no account of how it was derived. The manual states that serum iron depends on iron intake and is subject to circadian variation, and that hemoglobin iron released from damaged red cells gives falsely elevated results [2].
US national survey laboratory procedure manual, 2017 to 2018, women
Adult women, as the reference range printed for the serum assay · [2]
| Range | What the source calls it |
|---|---|
| below 37 µg/dL | No name given |
| 37 to 145 µg/dL | "reference range" |
| above 145 µg/dL | No name given |
From the same manual, with no account of how it was derived [2].
US national survey laboratory procedure manual, 2015 to 2016, men
Men, as the reference range printed for the assay · [3], [4]
| Range | What the source calls it |
|---|---|
| below 50 µg/dL | No name given |
| 50 to 160 µg/dL | "reference range" |
| above 160 µg/dL | No name given |
From the manual for the method used in the 2015 to 2016 survey (Beckman UniCel DxC 800, run by Collaborative Laboratory Services). The manual states that its reference ranges were established from wellness participants with an age mix similar to the laboratory's patients, and gives no ages for this range. It states that samples are to be drawn in the morning because of daily variation, and that a hemoglobin level of 60 mg/dL from hemolysis raises the result by 12 µg/dL [3]. The same laboratory's 2003 to 2004 manual prints the same range and equates 586 µg/dL of iron with 105 µmol/L, a factor of 0.179 [4]. Two assays used by the same national survey print different ranges [3][2].
US national survey laboratory procedure manual, 2015 to 2016, women
Women, as the reference range printed for the assay · [3], [4]
| Range | What the source calls it |
|---|---|
| below 40 µg/dL | No name given |
| 40 to 150 µg/dL | "reference range" |
| above 150 µg/dL | No name given |
From the same manual, established the same way. The 2003 to 2004 manual prints the same range [3][4].
US national survey laboratory procedure manual, 1999 to 2000, men
Men older than 18 · [5]
| Range | What the source calls it |
|---|---|
| below 60 µg/dL | No name given |
| 60 to 190 µg/dL | "normal range" |
| above 190 µg/dL | No name given |
The manual describes these as the normal ranges for the US population, based on the second national survey of 1976 to 1980, and does not say which percentiles they are. The line that prints the ranges gives the unit as µL/dL, while the manual's data table labels serum iron in µg/dL. The method was an automated colorimetric assay run at a Centers for Disease Control and Prevention laboratory. The upper limit is 32 µg/dL above the 2017 to 2018 manual's limit for men [5][2].
US national survey laboratory procedure manual, 1999 to 2000, women
Women older than 18 · [5]
| Range | What the source calls it |
|---|---|
| below 40 µg/dL | No name given |
| 40 to 175 µg/dL | "normal range" |
| above 175 µg/dL | No name given |
From the same manual and the same 1976 to 1980 survey data. The manual states that values for adult men are generally higher than those for adult women [5].
US national survey laboratory procedure manual, 1999 to 2000, children aged 3 to 17
Children aged 3 to 17 · [5]
| Range | What the source calls it |
|---|---|
| below 32 µg/dL | No name given |
| 32 to 175 µg/dL | "normal range" |
| above 175 µg/dL | No name given |
From the same manual and the same 1976 to 1980 survey data, as one range for boys and girls. The manual states that children have lower values than adults [5].
US national survey laboratory procedure manual, 1999 to 2000, level reported back to participants
Survey participants, as the level at which a result was reported back as possible iron deficiency · [5]
| Range | What the source calls it |
|---|---|
| below 30 µg/dL | "indicative of possible iron deficiency" |
| 30 or above µg/dL | No name given |
A notification rule for the survey, not a diagnostic criterion. The manual treats a serum iron below 30 µg/dL or a transferrin saturation below 15% as indicative of possible iron deficiency, and a saturation above 55% with ferritin above 300 ng/mL as possibly indicative of iron overload. It gives no serum iron level for iron overload, so this block does not classify high results. The manual defines no critical values for the test [5].
How it compares with the reference method
Mixed results3
Time of day
Mixed results: one study of 20 adults found no consistent daily pattern, while 276,307 community results averaged highest at 11:00 to 12:00.
The numbers and sources
- Compared with
- The same person's or the same population's morning result
- Effect
- In 20 healthy adults sampled at 8 AM, noon and 4 PM, then at 8 AM the next day, no consistent daily pattern was seen. Morning iron was higher than afternoon iron in only half of them, and variation between days was similar to variation within a day [10]. In 276,307 community test results, serum iron was relatively high from 8:00 to 15:00. Mean values were highest at 11:00 in adult men, at 12:00 in adult women and children, and as late as 15:00 in teenagers [11]. In 8 volunteers sampled across the day, serum iron followed a daily rhythm with a mean of 93.6 µg/dL, a swing of 26.4 µg/dL either side of it and a peak at 10:40 [12]. The 2015 to 2016 survey manual states that samples are to be drawn in the morning because of daily variation, and the 1998 US recommendations state that serum iron rises in the morning and falls at night [3][13].
- Population
- 20 healthy adult volunteers [10]. Community laboratory results in Calgary from 2011 to 2015 [11]. 8 healthy volunteers [12].
- Sources
- [10], [11], [12], [3], [13]
- Caveats
- The community study compared different people tested at different hours, not the same people through a day. The abstract of the 8-person study gives a peak at 10:40 and also states that evening levels were higher than morning levels [12]. The sources disagree on whether the hour of the draw matters.
Variation from one draw to the next in one person
Shown to vary about 28% from one draw to the next within the same person, in a pooled estimate from a European laboratory federation.
The numbers and sources
- Compared with
- The same person's results on repeated draws
- Effect
- The European Federation of Clinical Chemistry and Laboratory Medicine database gives a pooled within-person variation of 27.6% for serum iron, with lower and upper limits of 19.8% and 30.4%, from 4 included estimates. Variation between people is 26.7% [15]. At a serum iron of 100 µg/dL, 27.6% is about 28 µg/dL. The 1998 US recommendations state that day-to-day variation within a person is greater for serum iron than for hemoglobin or hematocrit [13].
- Population
- Healthy adults in the studies the database pools [15].
- Sources
- [15], [13]
- Caveats
- A summary across studies in healthy volunteers. The database states no threshold for agreement, so the result is given as numbers only. Variation within one person is as large as variation between people, so a single reading places a person only loosely within a reference range [15].
Detecting iron deficiency against ferritin
Limited evidence: in one laboratory study serum iron picked out iron deficiency less well than transferrin or total iron binding capacity, 0.77 against 0.94.
The numbers and sources
- Compared with
- Iron deficiency defined by serum ferritin below 12 or below 15 ng/mL
- Effect
- Across inpatients and outpatients and three reagent combinations, the mean area under the curve for identifying iron deficiency was 0.77 for serum iron, 0.87 for the saturation index and 0.94 for transferrin or total iron binding capacity [16]. The 1998 US recommendations state that infections and inflammation can lower serum iron [13].
- Population
- Laboratory requests with serum iron, transferrin or binding capacity, and ferritin measured together [16].
- Sources
- [16], [13]
- Caveats
- One retrospective laboratory study by a single author, which used ferritin and not bone marrow iron as the reference. The abstract gives no patient count and states no threshold for agreement, so the result is given as numbers only [16].
Did not match the reference method2
After a meal and by length of fast
Limited evidence: serum iron read higher for 4 hours after a light meal in 17 volunteers, and took about 5 hours to settle in community results.
The numbers and sources
- Compared with
- The same person's fasting result, or results after a 5 to 9 hour fast
- Effect
- In 17 volunteers who ate a light standardized meal after a fasting draw, serum iron was significantly higher 1, 2 and 4 hours later, and the change at 2 hours exceeded the limit the authors took from biological variation [14]. In 276,307 community results, serum iron in adults took approximately 5 hours after eating to return to a baseline. After 10 hours of fasting it rose gradually to higher levels than at shorter fasts, and the authors state that after 12 hours or more of fasting it may be elevated beyond otherwise usual levels [11]. The 1998 US recommendations state that serum iron increases after each meal [13].
- Population
- 17 healthy volunteers in Italy, 8 women and 9 men, mean age 29 [14]. Community laboratory results in Calgary [11].
- Sources
- [14], [11], [13]
- Caveats
- The text of the meal study gives no size for the rise. In the community study, children and teenage girls showed no significant change until after 11 hours of fasting [11].
After an iron tablet
One study of 8 volunteers found oral iron raised the daily mean of serum iron from 93.6 to 115.7 µg/dL and widened its daily swing.
The numbers and sources
- Compared with
- The same volunteers on a day with no iron taken
- Effect
- Volunteers were sampled across the day with no drug, then after ferrous sulfate supplying 66 mg of elemental iron and after an iron polymaltose complex supplying 100 mg, in random order a week apart. With oral iron, the mean of the daily rhythm rose from 93.6 to 115.7 µg/dL, the swing either side of the mean rose from 26.4 to 38.5 µg/dL, and the peak moved from 10:40 to 11:30. Ferrous sulfate produced a higher peak level and total exposure than the polymaltose complex [12]. The 2017 to 2018 survey manual states that the concentration of iron in serum depends on the ingestion of iron [2].
- Population
- 8 healthy volunteers in India [12].
- Sources
- [12], [2]
- Caveats
- One small study, which reports the change in the fitted daily rhythm, not the peak rise in the hours after a tablet. The abstract does not say which of the two iron products the rhythm figures belong to [12].
What studies tie it to
Linked in research3
Death from any cause
Limited evidence: one Taiwanese cohort linked both low and high serum iron to more deaths over 19 years, 27% and 37% more than the middle group.
The numbers and sources
- Effect
- The relation between serum iron and death from any cause, and from specific causes, was J-shaped. Against the group classed as normal, the adjusted hazard ratio for death was 1.27 (95% CI 1.23 to 1.31) in the low group and 1.37 (1.30 to 1.44) in the high group. People whose serum iron was outside the normal group at two visits had a hazard ratio of 1.49 (1.36 to 1.63) against people inside it at both [6].
- Population
- Adults in the Taiwan MJ health screening cohort, recruited 1997 to 2007 and followed to 2022, 33,005 deaths over a median of 19.0 years [6].
- Sources
- [6]
- Caveats
- One observational cohort. The abstract does not give the number of participants or the serum iron levels that defined the low and high groups. Illness that changes serum iron before death cannot be ruled out [6].
Coronary artery disease in a genetic study
Limited evidence: one genetic study found higher serum iron went with slightly less coronary artery disease, an odds ratio of 0.94 per standard deviation.
The numbers and sources
- Effect
- In a Mendelian randomization study using three gene variants tied to iron status, the odds ratio for coronary artery disease was 0.94 per standard deviation higher serum iron (95% CI 0.88 to 1.00, P = 0.039). Results for transferrin saturation (0.95, 0.91 to 0.99) and ferritin (0.85, 0.73 to 0.98) pointed the same way [7].
- Population
- Gene associations with iron status from 48,972 people, and with coronary artery disease from 60,801 cases and 123,504 controls combined with a second set of 63,746 cases and 130,681 controls [7].
- Sources
- [7]
- Caveats
- A genetic estimate of lifelong difference in iron status, resting on three variants, with a confidence interval that reaches 1.00. It does not show what a single high or low reading means, or what changing serum iron does [7].
Stroke in a genetic study
Limited evidence: one genetic study found higher serum iron went with slightly more stroke, an odds ratio of 1.07 per standard deviation.
The numbers and sources
- Effect
- In a Mendelian randomization study, the odds ratio for stroke was 1.07 per standard deviation higher genetically determined serum iron (95% CI 1.01 to 1.14), 1.06 for transferrin saturation (1.01 to 1.11) and 1.18 for ferritin (1.02 to 1.36). Among types of ischemic stroke, the finding was driven by cardioembolic stroke [8].
- Population
- Gene associations with iron status from 48,972 people, and with stroke from the MEGASTROKE consortium [8].
- Sources
- [8]
- Caveats
- The same gene variants pointed toward less coronary artery disease in a separate study, so the genetic evidence runs in opposite directions for two vascular outcomes [7][8].
Mixed results1
Cancer
Limited evidence: one Australian cohort linked higher serum iron to more cancer in women and to less cancer in men.
The numbers and sources
- Effect
- In women, higher serum iron had a hazard ratio of 1.83 (95% CI 1.21 to 2.76) for a new cancer other than skin cancer and 2.45 (1.12 to 5.34) for breast cancer. In men, higher serum iron had a hazard ratio of 0.65 (0.42 to 0.99) for a new cancer other than skin cancer and 0.34 (0.12 to 0.95) for colorectal cancer. Ferritin was not associated with cancer risk or cancer death [9].
- Population
- 1,597 men and 1,795 women aged 25 to 79 in the Busselton Health Survey, without cancer at the start and with ferritin of 20 ng/mL or above, followed from 1994 or 1995 to 2010 [9].
- Sources
- [9]
- Caveats
- One observational cohort, with opposite directions in women and men. The abstract does not state which serum iron levels were compared, and the authors call the basis for the sex difference unclear [9].
Related
Sources
- US Food and Drug Administration. 21 CFR 862.1410, Iron (non-heme) test system. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/section-862.1410
- Centers for Disease Control and Prevention, National Center for Health Statistics. National Health and Nutrition Examination Survey 2017-2018 Laboratory Procedure Manual: Iron (Frozen), serum, Roche Cobas 6000. Performed by the University of Minnesota Advanced Research and Diagnostic Laboratory. https://wwwn.cdc.gov/nchs/data/nhanes/public/2017/labmethods/FETIB-J-MET-Iron-(Frozen)-508.pdf
- Centers for Disease Control and Prevention, National Center for Health Statistics. National Health and Nutrition Examination Survey 2015-2016 Laboratory Procedure Manual: Iron, refrigerated serum, Beckman UniCel DxC 800 Synchron. Performed by Collaborative Laboratory Services. https://wwwn.cdc.gov/nchs/data/nhanes/public/2015/labmethods/BIOPRO_I_MET_IRON_DXC800and660i.pdf
- Centers for Disease Control and Prevention, National Center for Health Statistics. National Health and Nutrition Examination Survey 2003-2004 Laboratory Procedure Manual: Total Iron Binding Capacity (TIBC), serum, Beckman Synchron LX20. Performed by Collaborative Laboratory Services. https://wwwn.cdc.gov/nchs/data/nhanes/public/2003/labmethods/l40fe_c_met_tibc.pdf
- Centers for Disease Control and Prevention, National Center for Health Statistics. National Health and Nutrition Examination Survey 1999-2000 Laboratory Procedure Manual: Iron and TIBC, serum. Performed by the Inorganic Toxicology and Nutrition Branch, National Center for Environmental Health. https://wwwn.cdc.gov/nchs/data/nhanes/public/1999/labmethods/lab06_met_-fe_tibc.pdf
- Liu Y, Wen CP, Pan J, et al. Associations of serum iron and its status change with mortality risk: prospective findings from the MJ cohort. European Journal of Epidemiology. 2025. https://doi.org/10.1007/s10654-025-01295-w
- Gill D, Del Greco M F, Walker AP, et al. The Effect of Iron Status on Risk of Coronary Artery Disease: A Mendelian Randomization Study. Arteriosclerosis, Thrombosis, and Vascular Biology. 2017. https://doi.org/10.1161/ATVBAHA.117.309757
- Gill D, Monori G, Tzoulaki I, Dehghan A. Iron Status and Risk of Stroke. Stroke. 2018. https://doi.org/10.1161/STROKEAHA.118.022701
- Chua AC, Knuiman MW, Trinder D, et al. Higher concentrations of serum iron and transferrin saturation but not serum ferritin are associated with cancer outcomes. The American Journal of Clinical Nutrition. 2016. https://doi.org/10.3945/ajcn.115.129411
- Dale JC, Burritt MF, Zinsmeister AR. Diurnal Variation of Serum Iron, Iron-Binding Capacity, Transferrin Saturation, and Ferritin Levels. American Journal of Clinical Pathology. 2002. https://doi.org/10.1309/2YT4-CMP3-KYW7-9RK1
- Nguyen LT, Buse JD, Baskin L, Sadrzadeh SMH, Naugler C. Influence of diurnal variation and fasting on serum iron concentrations in a community-based population. Clinical Biochemistry. 2017. https://doi.org/10.1016/j.clinbiochem.2017.09.018
- Malhotra S, Garg SK, Khullar GK, et al. Kinetics of two different iron formulations and their effect on diurnal variation of serum iron levels. Methods and Findings in Experimental and Clinical Pharmacology. 2004. https://doi.org/10.1358/mf.2004.26.6.831316
- Centers for Disease Control and Prevention. Recommendations to Prevent and Control Iron Deficiency in the United States. MMWR Recommendations and Reports. 1998;47(RR-3). https://www.cdc.gov/mmwr/preview/mmwrhtml/00051880.htm
- Lima-Oliveira G, Salvagno GL, Lippi G, et al. Influence of a Regular, Standardized Meal on Clinical Chemistry Analytes. Annals of Laboratory Medicine. 2012. https://doi.org/10.3343/alm.2012.32.4.250
- European Federation of Clinical Chemistry and Laboratory Medicine. EFLM Biological Variation Database, meta-analysis estimates, read 2026-11-13. https://biologicalvariation.eu/
- Hawkins RC. Total iron binding capacity or transferrin concentration alone outperforms iron and saturation indices in predicting iron deficiency. Clinica Chimica Acta. 2007. https://doi.org/10.1016/j.cca.2007.02.032