Iron Deficiency Is Common in Anemic Elderly Patients: Results with sTfr Index.
Authors: Yang Mindy M. , Ann Mary , Riordan Dawn E. , Fu Min , Moyo Victor , Woodman Richard C. 
Published: April 2020

Chronic anemia is common in the elderly (≥65) with a prevalence often exceeding 10%. Multiple comorbidities and multiple causes of anemia complicate anemia diagnosis in the elderly. Iron deficiency anemia (IDA) and anemia of chronic inflammation (ACI) both commonly occur in the elderly. Distinguishing ACI from the combination of IDA and ACI is difficult with conventional tests (serum iron, TIBC, TSAT, and ferritin), especially in elderly patients or those with multiple comorbidities. Recently, the serum transferrin receptor (sTfr) has been recommended to assess iron stores, although there is limited data in the elderly. Unlike ferritin, TIBC, or TSAT, sTfr Index (sTfr(mg/L)/[log10ferritin]) is not influenced by pro-inflammatory cytokines and may provide a more precise classification of iron status.

Purpose: To determine the occurrence of iron deficiency alone or in combination with ACI in the elderly using the sTfr Index.

Methods: The results of the sTfr Index were compared to ferritin, as well as serum iron, TIBC, and TSAT to determine the presence of iron deficiency alone or in combination with ACI. An sTfr Index of ≥2.0 was used to define iron deficiency. Data were obtained from ambulatory, community-dwelling elderly screened for three clinical trials for treatment of chronic anemia (Hb≤11g/dL x &gt;3 months) using epoetin alfa. No patients had a history of GI bleeding, active cancer, or recent infections. At the time of evaluation, no patients were receiving iron therapy. GFR was calculated using the Modification of Diet for Renal Disease (MDRD) Equation.

Results: A total of 81 patients (mean age 75±6, range 66–89 years; 68 women and 13 men) were studied. Of these patients, 43 patients had a history of rheumatoid arthritis. 32% were African-American, 64% Caucasian, and 4% Hispanic/American-Indian. For the entire cohort, mean Hb was 10.3±0.9 g/dL; ferritin 148.0±180.9ng/mL; iron 61±33mcg/mL; TIBC 311±69mcg/dL (n=80); TSAT 19.7±11.0%; GFR 59.2±28.0mL/min/1.73m2 (n=78); sTfr Index was 3.02±3.16. There was no statistically significant difference in the severity of anemia between patients with and without iron deficiency (sTfr Index ≥2.0, Hb 10.3±0.8 vs. sTfr Index &lt;2.0, Hb 10.4±1.0g/dL). The following table summarizes the distribution of sTfr Index stratified by ferritin concentration. Twenty-six of 35 (74%) patients with a ferritin 30–100 ng/mL had sTfr Index ≥2.0 consistent with iron deficiency. However, using conventional iron tests (meeting 2 of 3 criteria: TIBC &gt;450mcg/dL, iron &lt;60mcg/dL, TSAT &lt;15%), only 19 of the 26 patients would have been identified as having IDA. Surprisingly, 9 of 33 (27%) patients with ferritin &gt;100ng/mL also had sTfr Index ≥2.0 suggesting functional iron deficiency in combination with ACI. Among all patients included in this analysis, compared to conventional iron tests, an univariate logistic regression analysis showed that with each unit increase in sTfr Index, the odds of being iron deficient, identified by conventional tests, significantly increased 3.4-fold (p&lt;0.0001, 95% CI: 1.8–6.1).

Conclusions: Results with the sTfr Index suggest that iron deficiency in the elderly may be more common than reported with conventional iron tests. In community-dwelling elderly patients with ferritin levels consistent with ACI (&gt;100ng/mL) may have concomitant functional iron deficiency. The use of sTfr in older adults with milder anemia (Hb&gt;11g/dL) should also be evaluated.

Ferritin (ng/mL) sTfr Index &lt; 30 30–100 &gt; 100 &lt; 2.0 0 9 24 2.0 – 3.0 1 17 5 &gt;3.0 12 9 4 Total 13 35 33