The Cutoff Value of Serum Ferritin for the Diagnosis of Iron Deficiency in the Community-Residing Older Persons.
Authors: Choi Chul Won , Yoon Soo-Young , Park Kyong Hwa , Choi In Keun , Kim Seok Jin , Seo Jae Hong , Kim Byung Soo , Shin Sang Won , Kim Yeul Hong , Kim Jun Suk , Lee Juneyoung 
Published: April 2020

Abstract
Two most common causes of anemia in older adults are anemia of chronic disease (ACD) and iron deficiency. The diagnosis of iron deficiency is important because the proper iron therapy can improve the symptoms as well as it may indicate the occult gastrointestinal pathology such as malignancy. Although the confirmation of the absence of iron storage in the bone marrow aspirate sample should be the “gold standard” for the diagnosis of iron deficiency, the value of less invasive tests assessing iron storage in general populations has been well established. The serum ferritin assay is the best single blood test for the diagnosis of iron deficiency. The interpretation in older adults is complicated sometimes due to the serum ferritin level increasing with age. Moreover, in the case of concomitant chronic disorders which are common in older adults, the serum ferritin level is increased in spite of iron deficiency. This implies that the application of the cutoff point derived from younger populations to the elderly is inappropriate. The desirable ferritin cutoff value for the diagnosis of iron deficiency has been suggested approximately 45 μg/L for older adults, comparing to the lower concentration of 12 μg/L for young adults. However, the study was performed with hospitalized anemic patients. It thus is required to verify whether the ferritin cutoff value could be applied to community-dwelling older adults. As the level of soluble transferrin receptor (sTfR) is not influenced by ageing or chronic diseases, the assay measuring sTfR has been developed with the indication for the diagnosis of iron deficiency. To make the test more specific, the application of the ratio of sTfR to the log ferritin level (sTfR-F index) has been suggested. The index value greater than 1.5 was diagnosed as iron deficiency. Since routine screening of iron deficiency by the bone marrow examination is not feasible for the community-residing, fully ambulatory older persons, we used sTfR-F index as the standard for iron deficiency instead of the bone marrow aspiration. Here, we prospectively determined the normal minimum level of the serum ferritin for the community-dwelling older adults using the sTfR-F index. We conducted the anemia survey between October 2002 and November 2002. 1,254 apparently healthy older adults aged between 60 and 95 years from three urban community-dwellings were participated in the survey. Among these individuals, 156 subjects who were anemic or whose serum ferritin level was less than 100 μg/L were selected. The soluble transferrin receptor assay was performed and the sTfR-F index was calculated. The receiver operating characteristic (ROC) curve analysis was performed. Based on the data, the serum ferritin level 22 μg/L was selected as the cutoff for the diagnosis of iron deficiency in the community-dwelling older adults. Applying the serum ferritin cutoff 22 μg/L and the sTfR-F index cutoff 1.5, the sensitivity of the assay was 89.5% (34/38) and the specificity was 89.0% (105/118). In conclusion, for the diagnosis of iron deficiency of community-residing older adults, we suggest the serum ferritin cutoff 22 μg/L by use of the sTfR-F index. The value is lower than the previous value established in hospitalized and anemic older adults.