Iron deficiency anemia (IDA) is a common health condition with increasing prevalence worldwide^1,2). The diagnostic criteria for IDA includes a myriad of laboratory values to be considered for the diagnosis, namely a low hemoglobin (<7.7 mmol/L in men and 7.4 mmol/L in women], a low serum iron (<7.1µg/L), a low serum ferritin - the storage form of iron (<30 ng/L), a low transferrin saturation (<15%), and a high total iron-binding capacity (>13.1 µmol/L)³⁾. This observation is even more pertinent in the U.S. where the prevalence of anemia has nearly doubled (4.0% to 7.1%). Risk factors for IDA include age and comorbidities like diabetes and congestive heart failure⁴⁾. The IDA status of patients is important to consider in invasive procedures such as orthopedic surgeries where it associated with extended recovery time, a longer length of stay, increased readmission rates, and higher costs of care^1,5).

Current literature supports IDA as an independent risk factor in orthopedic procedures, but there is a lack of research investigating the impact of IDA on revision total hip arthroplasty (RTHA). Nesslage et al.⁶⁾ found IDA is associated with greater risks of revision following primary total hip arthroplasty (THA). In a recent retrospective cohort study, Sim et al.⁷⁾ found preoperative anemia is associated with poorer physical function and health-related quality of life after hip fracture surgery. Furthermore, in a prospective observational cohort study, Halm et al.⁵⁾ demonstrated that higher preoperative hemoglobin was associated with shorter length of stay and lower odds of death and readmission within 60 days of discharge following hip fracture surgery. The aforementioned studies suggest IDA is an important risk factor to consider in THA and hip fracture surgery due to its significant impact on patient outcomes. However, the relationship between IDA and outcome following RTHA has not been assessed, and with an increasing prevalence of IDA and need for RTHA, further evaluation of this link is warranted. As such, the purpose of this study is to determine whether IDA patients undergoing RTHA have increased: 1) in-hospital lengths of stay (LOS); 2) medical complications; and 3) costs of care.

Anemia prevalence in the US has increased from 4.0% to 7.1%, nearly doubling from 2003–2004 to 2011–2012¹⁴⁾. While it is suggested that IDA is generally linked to worse surgical outcomes, research on its impact on RTHA is still lacking^1,4,5). As such, a nationwide administrative claims database was used to research the association of IDA with outcomes following RTHA. After adjusting for age, sex, and medical comorbidities the current study of over 92,000 patients demonstrated that IDA is associated with a significant increase in-hospital LOS, increased incidence and odds of 90-day medical complications, and increased cost of care both on the day of the surgery and during 90 days postoperative. This study is important as it provides information that can help elucidate possible postoperative complications in IDA patients.

While the study is well-powered, it is not without limitations. Some of these limitations are inherent to retrospective studies, where the accuracy of the data cannot be fully ascertained. Patients and complications were identified using the ICD-9 codes, which is not exempted from misdiagnoses and errors¹⁵⁾. The accuracy of our data is therefore highly dependent on the accuracy of the ICD-9 codes. Although we have matched for age, sex, and medical comorbidities, measurement of outcome still is subject to errors that cannot be accounted for such as worse outcome due to human error or malpractice. Furthermore, IDA cannot be completely identified as an independent variable because low iron levels diagnosed as IDA could be one symptom of a larger, underlying, undiscovered medical condition. For instance, IDA could potentially be an indicator of other underlying medical conditions such as chronic kidney disease, as such, these complications can naturally occur in this patient population. Given this possibility, it is questionable whether the results of this study can be summarized exclusively to patients who have IDA. Therefore, our study is limited to the impact of IDA on RTHA outcome based on ICD-9 IDA diagnosis and our given data, not necessarily IDA itself. Due to limitations of the PearlDiver platform, we were unable to ascertain laboratory markers to further ensure that patients truly had IDA, and to determine the association of IDA with outcomes in patients undergoing the revision procedure. However, this can serve as the basis for future prospective studies as our study provides statistically significant information where the literature is insufficient. This study is a foundation, i suggesting directions for future studies that can further explore the identified relationship between IDA and RTHA outcomes. Further studies are needed to quantify the impact of IDA severity and duration on outcome following RTHA.

There is limited research on the subject of IDA and its impact following RTHA. Nonetheless, our assessment of the link between IDA and outcome following RTHA is echoed by similar studies^{5,16,17,18,19,20)}. In a retrospective analysis of 146 elective RTHA patients, Mahadevan et al.¹⁶⁾ found that LOS was significantly increased in patients who received transfusions. Transfusion requirements were greater in patients who had lower preoperative hemoglobin concentration, thus anemic patients. Mahadevan et al.¹⁶⁾ also found that LOS was linked to an increase in age with patients that were 80 and older having a LOS of 22 days. That is nearly doubled the LOS of patients that were below 60 years old. Notably, given the low sample size, there is some question as to the power of the study.

Our findings have identified that IDA is associated with higher incidence and odds of medical complications. In a prospective study, Dunne et al.¹⁷⁾ reported an increased incidence of pneumonia from 2.6% to 5.0% with an increasing degree of anemia. Furthermore, low preoperative hematocrit, low postoperative hematocrit, and increased blood transfusion rates were associated with increased mortality (P<0.01), increased postoperative pneumonia (P<0.05 or P=0.05), and increased hospital length of stay (P<0.05)¹⁷⁾. Similarly, in a retrospective cohort study of 7,759 consecutive noncardiac surgical patients, Beattie et al.¹⁸⁾ found that preoperative anemia was associated with a nearly 5-fold increase in the odds of postoperative mortality. After adjusting for major confounders using logistic regression, anemia was still associated with increased mortality (OR 2.36, 95% CI 1.57–3.41). Additionally, Wu et al.²⁰⁾ found an OR of 1.6 (95% CI 1.1–2.2) increase in 30-day postoperative mortality associated with a decrease in hematocrit value. Further analysis showed an increased 30-day cardiac morbidity linked to a hematocrit level of 39%. Musallam et al.²¹⁾ went further and categorized the study group depending on anemia severity. Results show that increased anemia severity is linked to higher morbidity, as shown by an OR of 1.31 (95% CI 1.26–1.36) in mildly anemic patients and 1.56 (95% CI 1.47–1.66) in moderately-to-severely anemic patients²¹⁾. Richards et al.²²⁾ analyzed the impact of preoperative anemia and blood transfusion on postoperative outcomes in gynecological surgery, which monitored outcomes similar to the current study. After adjusting for cofounders, Richards et al.²²⁾ found that preoperative anemia was independently and significantly associated with increased odds of 30-day mortality (OR 2.40, 95% CI 1.06–5.44) and composite morbidity (OR 1.80, 95% CI 1.45–2.24). The study group had a significantly higher odds of all tested morbidities (respiratory, central nervous system, renal, wound, sepsis, and venous thrombosis).

IDA increases the incidence and odds of medical complications in RTHA patients which can lead to higher cost of care. Feng et al.¹⁹⁾ studied hospital costs associated with anemia in elective colorectal surgery. In this study, they found that anemia was associated with an adjusted 14% relative increase in costs. The total hospitalization cost attributable to anemia was 3,027 CAD (95% CI 2,670–3,388). As such, minimizing healthcare expenditures within this population is of critical importance, and can be achieved with adequate preoperative optimization. Studies have shown that treatment for IDA can be executed either with oral or intravenous supplementation, as both have been shown to restore hemoglobin concentrations, reduce the incidence of postoperative transfusion requirements, and have increased quality of life in patients^23,24,25). The time period between the primary diagnosis of the condition and the surgical intervention is the main determinant on whether patients should receive oral or intravenous iron^26,27). Those patients who have longer than 6 weeks until their surgery can be optimized with oral supplementation with either 40 to 60 mg of elemental iron daily, or 80 to 100 mg, every other day. Hemoglobin values should be assessed 4 weeks after initial administration of oral iron. For those patients who are still anemic, they should be changed to intravenous iron supplementation^27,28). Studies have found intravenous formulation to be safe^29,30). In a study of 10,390 patients who received intravenous iron treatment, there was no increased risk of adverse events with a relative risk of 1.04 (95% CI 0.93–1.17)²⁹⁾.

Some studies in the literature yielded opposite findings about the relationship between IDA and RTHA outcomes. Waters et al.³¹⁾ studied the prevalence of iron deficiency in a total joint surgery population, where no association was found between simple iron deficiency and any perioperative complications. However only ferritin was considered as a marker for iron deficiency. Furthermore, only one hundred patients were studied, which puts to question the power of the study. Similarly, Vuille-Lessard et al.³²⁾ and So-Osman et al.³³⁾ found no association between postoperative anemia and poor outcome when compared to a patient without blood loss. These studies examined postoperative anemia, caused mostly by blood loss from surgery, rather than preoperative anemia.

The current study found IDA to be associated with longer in-hospital LOS, as well as higher rates of complications and costs. Adjusting for baseline covariates, the association of adverse events in IDA patients persisted. Future prospective studies should evaluate the severity of IDA with laboratory markers for primary and revision total joint arthroplasty procedures. Prior optimization can potentially help to mitigate many of these adverse events and potentially reduce the high costs associated with this comorbidity. The current study can be utilized by healthcare professionals and orthopaedic surgeons to adequately educate these patients of the complications which may occur following their revision procedure.