Anemia as a Complication of Bariatric Surgery: Frequency and Evidence for Progressive Negative Iron Balance.
Authors: von Drygalski Annette , Andris Deborah A. , Jackson Scott , Nuttleman Peter R. , Klein J. , Wallace James R. 
Published: April 2020

Abstract
Bariatric surgery has become an important means to reduce obesity and its related morbidity. Bariatric surgeries in the US have increased from 14,000 in 1998 to 140,000 in 2004. Malabsorption and achlorhydria can complicate bariatric surgery and may lead to iron deficiency and anemia. In this setting, little is known about the prevalence and severity of anemia and the efficacy of oral iron replacement, a common part of post-surgical management. We reviewed the records at our institution of a large number (n=1125; 126 men; 999 women) of patients followed for up to 4 yrs post-procedure for the development of anemia and assessment of vitamin levels and iron stores.
METHODS: Body mass index (BMI), hemoglobin (Hb), B12, folate, serum iron and ferritin values were extracted from electronic records of the patients at baseline, and 250 patients (33 men; 217 women) followed out to 4 yrs after Roux-en-Y gastric bypass. Anemia was defined by age- and gender-specific WHO criteria.
RESULTS: Mean BMI fell from 50.1 (CI 49.6–50.6) at baseline to 33.1 (CI 29.8–36.4) at 4 yrs. Anemia was present in 12% of all patients at baseline and was similar between men (9%) and women (12%). At 18mos, 29% of woman &lt;50yrs of age were anemic, compared to 9% of women &gt;50 yrs (p=0.02). For patients followed out to 2–4 yrs, 21% were anemic and women &lt;50 yrs were most affected (29%) compared to women &gt;50 yrs (15%; p=0.02). The incidence of anemia among men did not change over the period of observation. In all patients the mean Hb decreased from 13.4 g/dL (CI 13.3–13.5) at baseline to 12.1 g/dL (CI 11.1–13.1; p&lt;0.05) at 4yrs. Mean Hb in anemics was 10.4 g/dL. Baseline ferritin was 87 ng/mL (CI 75.2–99.7) for all patients and fell to 66 ng/mL(CI 51.2–80.0) at 18mos and 55 ng/mL (CI 43.3–66.2) by 2–4yrs. The percent of patients with ferritins &lt;50 and &lt;20 ng/mL at baseline were 23 and 11, respectively, and, of these, 15 and 25% were anemic. By yr 4, the percent of patients with ferritins &lt;50 ng/mL rose to 66 and 21% were anemic; the percent with ferritin &lt;20 was 4% and 33% were anemic. Again, women &lt;50 yrs were most at risk with a mean ferritin of 35 ng/mL (CI 21.8–48.2); of these 5% had a ferritin &lt;20 ng/mL and 37% of those were anemic. Of women &gt; 50 years, the mean ferritin was 63 ng/mL (CI 45.3–80.5); 54% had ferritins &lt;50 ng/mL and, of these, only 15% were anemic (p=0.04). Of the 4% with a ferritin &lt;20 ng/mL, 25% were anemic. Mean B12 and folate levels remained stable and did not correlate with anemia. In contrast to ferritin, mean serum iron values did not decrease. Interpretation of this finding is difficult since total iron binding capacity was not measured simultaneously and supplemental iron intake might be confounding.
CONCLUSIONS: although oral iron, folate and vitamin B12 supplements were routinely prescribed after surgery, anemia was a common complication and its frequency increased with time. Negative iron balance was progressive, despite oral iron supplementation. While iron deficiency did not account for all cases of anemia, it is sufficiently common to warrant careful evaluation of the ability of bariatric patients to absorb iron and/or comply with life-long oral iron supplementation. Given the rapidly increasing number of bariatric procedures in the US, all physicians should be alerted to the possible need for parenteral iron therapy to prevent anemia and its complications.