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Iron needs and chronic kidney disease in cats

Gest J, Langston C, Eatroff A. Iron status of cats with chronic kidney disease. J Vet Intern Med. 2015 Nov;(6):1488-1493.

Anemia is a serious concern as a secondary complication in cats with chronic kidney disease (CKD). In one prior study, anemia was found in 57% of cats with CKD, where the median survival time was 100 days once anemia developed. The main contributor to the cause of anemia is inadequate erythropoietin production by diseased kidneys.  One other possible mechanism is an absolute iron deficiency, secondary to: reduced oral iron intake, decreased gastrointestinal absorption or loss through gastrointestinal bleeding. A functional iron deficiency can develop when there is an inability to use otherwise adequate body iron stores for red blood cell (RBC) production. Few studies have looked at the iron status in cats with anemia due to CKD.

The objective of this study was to compare different indicators of iron status in cats with CKD versus healthy cats and cats with systemic nonrenal illness (NRI). Of the three groups evaluated, there were 39 cats in the healthy group, 40 cats with CKD, and 34 cats in the NRI group. The laboratory values measured were complete blood counts, serum chemistries, serum iron concentrations, total iron binding capacity (TIBC), and ferritin concentrations and percent transferrin saturation (TSAT) calculated on all the cats.

When the results were evaluated, total iron binding capacity was found to be significantly lower in CKD cats versus healthy cats.  No significant difference though was found for TIBC between CKD and NRI groups or between the Healthy cat group and NRI cats. Also, there was no significant difference detected among any of the groups for serum iron concentrations or ferritin concentrations. Among the CKD cats, 32 were classified as non-anemic and 8 as anemic where anemia was defined as a hemoglobin <9.5 g/dL.

Of an interesting note, TIBC is decreased in inflammation. With TIBC significantly lower in cats with CKD compared to health cats, this study’s results support the presence of inflammation in this group of CKD cats. TSAT and MCV (mean corpuscular volume)-a microcystosis- were significantly lower in anemic cats compared to non-anemic cats with CKD. This indicates a finding of both an absolute and a functional iron deficiency. The functional anemia is likely secondary to decreased erythropoiesis by diseased kidneys as well as anemia of inflammation. (VT)

See also:
Mercadal L, Metzger M, et al. A 3-marker index improves the identification of iron disorders in CKD anaemia. PLoS One. 2014 Feb 19;9(2):e84144.