Increased ferritin may be transitory due to acute inflammation, or chronic due to chronic inflammation or iron storage disorders such as hemochromatosis. Ferritin can sequester iron and make it unavailable for use. Ferritin is low in iron deficiency
Ferritin is the major iron storage protein in the body, and under normal circumstances, serum ferritin will reflect the amount of iron in storage. In general, 1 ng/mL of serum iron represents 8 mg of stored iron. However, serum levels can increase with inflammation, transfusions, hemosiderosis, hemochromatosis, liver disease, and certain anemias (iron deficiency, megaloblastic, or hemolytic) (Pagana 2019).
Low serum ferritin will be seen in iron deficiency.
Elevated ferritin is also seen with infection, malignancy, kidney disease, and inflammatory disorders such as rheumatoid arthritis and other autoimmune disorders. As an acute-phase protein, ferritin will sequester iron and make it unavailable for the production of red blood cells and other blood-based components. This process is considered to be protective as it limits the iron available for use by cancer cells and pathogens. So, ironically, you may see anemia associated with elevated ferritin (Wang 2010).
Research in the general population found that very high ferritin in men (194-598 ng/mL) significantly increased the risk of all-cause and cardiovascular mortality even in those without a history of chronic or cardiovascular disease (Kadoglou 2017).
In postmenopausal women, serum ferritin levels were significantly higher in obese individuals with metabolic syndrome and diabetes. The increased ferritin is likely due to the inflammatory nature of these metabolic disorders and likely not due to iron overload (Lecube 2005).
Kadoglou, Nikolaos P E et al. “The association of ferritin with cardiovascular and all-cause mortality in community-dwellers: The English longitudinal study of ageing.” PloS one vol. 12,6 e0178994. 7 Jun. 2017, doi:10.1371/journal.pone.0178994
Lecube, A et al. “Factors accounting for high ferritin levels in obesity.” International journal of obesity (2005) vol. 32,11 (2008): 1665-9. doi:10.1038/ijo.2008.154
Pagana, Kathleen Deska; Pagana, Timothy J.; Pagana, Theresa N. Mosby's Diagnostic and Laboratory Test Reference. Elsevier Health Sciences. 2019.
Wang, Wei et al. “Serum ferritin: Past, present and future.” Biochimica et biophysica acta vol. 1800,8 (2010): 760-9. doi:10.1016/j.bbagen.2010.03.011