Interpretation of serum ferritin concentrations as indicators of total-body iron stores in survey populations: the role of biomarkers for the acute phase response.
BACKGROUND
Nutritional surveys use acute phase protein (APP) biomarkers such as C-reactive protein (CRP) and alpha1-acid glycoprotein (AGP) to identify the influence of inflammation on the distribution of iron status biomarkers. Few, however, have examined which biomarker better identifies persons with spurious elevations in iron status markers.


OBJECTIVE
We explored the relations of APP biomarkers to iron-status biomarkers in infants and school-age children.


METHODS
In screening surveys, we identified a sample of African American infants (n = 351) and Guatemalan school-age children (n = 375). We used a common set of APP and iron-status biomarkers to examine the association between the 2 sets of markers (laboratory variables).


RESULTS
The overall prevalence of either inflammation or iron deficiency was <10% in both samples. The log AGP and CRP values were significantly correlated (r = 0.70), but the unexplained variance still was >50%. Serum ferritin-but not transferrin receptor, transferrin receptor index, or serum iron-was related to APP concentrations, but poor positive predictive value (<72%) and low kappa scores were found. Ferritin concentrations >1 geometric SD above the geometric mean were poorly predicted by either elevated AGP or CRP. Qualitative CRP analysis was not effective in identifying persons who had other indications of mild inflammation.


CONCLUSIONS
These analyses show that a low prevalence of inflammation has little influence on the distribution of ferritin, and 2 common indicators of inflammation do not perform equally well in identifying persons who may have elevations in ferritin due to inflammation.
Beard
John L
JL
Department of Nutritional Sciences, The Pennsylvania State University, University Park, PA 16802, USA. jbeard@psu.edu
Murray-Kolb
Laura E
LE
Rosales
Francisco J
FJ
Solomons
Noel W
NW
Angelilli
Mary Lu
ML
D000209:Acute-Phase Proteins / Q000032:analysis*; D000210:Acute-Phase Reaction / Q000097:blood*; D018798:Anemia, Iron-Deficiency / Q000097:blood / Q000175:diagnosis / Q000453:epidemiology*; D015415:Biomarkers / Q000032:analysis / Q000097:blood; D002097:C-Reactive Protein / Q000032:analysis; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D005293:Ferritins / Q000097:blood*; D006166:Guatemala / Q000453:epidemiology; D006801:Humans; D007223:Infant; D007249:Inflammation / Q000097:blood / Q000175:diagnosis / Q000453:epidemiology; D007501:Iron / Q000378:metabolism*; D019266:Iron, Dietary / Q000008:administration & dosage; D008297:Male; D008824:Michigan / Q000453:epidemiology; D009752:Nutritional Status; D009961:Orosomucoid / Q000032:analysis; D010865:Pilot Projects; D011237:Predictive Value of Tests
D000209:Acute-Phase Proteins; D015415:Biomarkers; D019266:Iron, Dietary; D009961:Orosomucoid; D002097:C-Reactive Protein; D005293:Ferritins; D007501:Iron