Abstract
BackgroundIron deficiency (ID) may impair long-term neurological development when it occurs in young infants. In cohort studies, it is sometimes necessary to evaluate ID with sera kept frozen for several years. To assess ID, learned societies recommend measuring serum ferritin (SF) level combined with C-reactive protein level. The long-term stability of C-reactive protein in frozen samples is well established but not ferritin.MethodsWe measured SF level (immunoturbidimetric assay; in micrograms per liter) immediately after collection from 53 young adults recruited and followed-up in Porto, Portugal, from 2011 to 2013 (SF1), and then, in 2016 in two aliquots kept frozen at– 80°C for 3 to 5 years: one without (SF2A) and one with (SF2B) intermediate thawing in 2014. We compared SF1 to SF2A then SF2B; statistical agreement was evaluated by the Bland and Altman method and the effect of intermediate thawing by regression modelling.ResultsMean SF2A–SF1 and SF2B–SF1 differences were -2.1 (SD 7.0) and 48.9 (SD 66.9). Values for Bland and Altman 95% limits of agreement were higher for the comparison of SF2B and SF1 than SF2A and SF1: -82.2 to 179.9 and -15.8 to 11.8, respectively; the effect of thawing was highly significant (p <0.001).ConclusionsAgreement between SF values before and after 3 to 5 years of constant freezing at -80°C was in a generally accepted range, which supports the hypothesis of ferritin’s stability at this temperature for a long period. In long-term storage by freezing, intermediate thawing induced a major increase in values.
Highlights
Iron deficiency (ID) is considered the most frequent micronutrient deficiency worldwide, including in industrialized countries [1], and is suspected to be associated with adverse shortand long-term neurocognitive sequelae when it occurs in young people [2,3,4,5]
To assess ID, learned societies recommend measuring serum ferritin (SF) level combined with C-reactive protein level
Values for Bland and Altman 95% limits of agreement were higher for the comparison of SF2B and SF1 than SF2A and SF1: -82.2 to 179.9 and -15.8 to 11.8, respectively; the effect of thawing was highly significant (p
Summary
Iron deficiency (ID) is considered the most frequent micronutrient deficiency worldwide, including in industrialized countries [1], and is suspected to be associated with adverse shortand long-term neurocognitive sequelae when it occurs in young people [2,3,4,5]. In cohort studies, including birth ones, it is sometimes necessary to evaluate ID with sera stored for several years, with or without intermediate thawing. The World Health Organization, American Academy of Pediatrics and European Food Safety Authority recommend using serum ferritin (SF) level to measure ID [1, 6, 9]. Iron deficiency (ID) may impair long-term neurological development when it occurs in young infants. It is sometimes necessary to evaluate ID with sera kept frozen for several years. To assess ID, learned societies recommend measuring serum ferritin (SF) level combined with C-reactive protein level. The long-term stability of C-reactive protein in frozen samples is well established but not ferritin
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