The prevalence of anemia in people with chronic kidney disease after hematopoietic stem cell transplantation
The hematopoietic stem cell transplantation includes peripheral blood stem cell transplantation, bone marrow, and umbilical cord transplant. This therapy is performed annually in approximately 50,000 patients with various hematological diseases. It is worth emphasizing that HSCT can damage the kidneys and this is called HSCT nephropathy . Chronic kidney disease (CKD) after HSCT occurs at a rate more than twice that observed in the general population . HSCT nephropathy is classified into two types: one type develops in the early stages (up to 3 months), and kidney damage is caused by sepsis or drugs administered during preconditioning and/or after HSCT. The second type (over 3 months) is caused by calcineurin inhibitors or due to a development of graft versus host disease (GVHD) . Anemia is a common complication of chronic kidney disease in patients with bone marrow transplantation and is associated with a deterioration in quality of life. In addition, it is a risk factor for mortality and accelerated CKD progression. One of the causes of anemia in CKD is an impaired bone marrow response to erythropoietin caused by uremic toxins, inflammation, reduced iron availability, or vitamin deficiencies (vitamin B12 or folate) . It is worth mentioning that anemia after HSCT is not just caused by chronic kidney disease . Anemia can occur in people after bone marrow transplantation with normal kidney function. Some patients after bone marrow transplant still require red blood cell transfusions for up to 1 year. This is often due to delayed regeneration of erythroid and ineffective stimulation of erythroid progenitor cells by erythropoietin . 

The aim of this study is to evaluate the relationship between CKD and the occurrence of anemia in patients at least 3 months after bone marrow transplantation. 

In this study, we described 156 patients after bone marrow transplantation from 1998–2021 in the Department of Hematology, Transplantation and Internal Disease, Medical University in Warsaw, Poland. Clinical and biochemical parameters are presented in and . We assessed hemoglobin concentration at least 3 months after bone marrow transplantation, and kidney function at least 3 months after bone marrow transplantation. Anemia was defined according to WHO criteria . CKD was defined as a persistent decrease in eGFR to below 60 mL/min/1.73 m 2 , or the presence of other abnormalities according to the definition of KDIGO . This study was approved by the local Ethical Committee in agreement with institutional guidelines. Informed consent was waived by the Ethical Committee due to the retrospective and non-interventional nature of the study. 

The study includes 156 patients who underwent allogeneic HSCT treatment in our center in the years 1998 to 2021 because of different hematologic pathologies (acute myeloid leukemia, n = 67, acute lymphoblastic leukemia, n = 31, lymphoma, n = 12 and other, n = 46) (data given in ). The other indications for HSCT were as follows: myelodysplastic syndrome ( n = 12), primary myelofibrosis, ( n = 8), aplastic anemia ( n = 6), AL amyloidosis ( n = 1), leukemia with mixed phenotype-MPAL ( n = 1), chronic myelomonocytic leukemia ( n = 6), chronic myelocytic leukemia ( n = 6), chronic lymphoblastic leukemia ( n = 3), Waldenstrom macroglobulinemia ( n = 1), multiple myeloma ( n = 1), Emberger syndrome ( n = 1), All patients were studied more than 100 days after HSCT to avoid complications caused by acute GVHD. Hemoglobin parameters in HSCT recipients are presented in . Anemia was diagnosed in 13% of women and 35% of men. Anemia was most common in people with HSCT due to acute myeloid leukemia (55% women, 30% men). In 56% of women and 17% of men, anemia was associated with chronic kidney disease as defined by KDIGO . presents the comparison between patients with and without anemia. Those with anemia had a more frequent history of acute lymphoblastic anemia. Other patients with anemia had a history of myelodysplastic syndrome-MDS ( n = 5), aplastic anemia ( n = 2), AL amyloidosis ( n = 1), primary myelofibrosis ( n = 3), leukemia with mixed phenotype-MPAL ( n = 1). Additionally, presents a comparison of patients with and without CKD. More frequently patients with CKD had a history of acute lymphoblastic leukemia and lymphoma. Patients with CKD had also a history of chronic myelomonocytic leukemia ( n = 1), chronic lymphoblastic anemia ( n = 1), primary myelofibrosis ( n = 2), myelodysplastic syndrome ( n = 1) and AL amyloidosis ( n = 1). 

As it is well known, anemia is one of the common complications of chronic kidney disease. Its main cause is insufficient production of endogenous erythropoietin, and impaired bone marrow response to erythropoietin, which is caused by uremic toxins, and inflammation. It is also worth mentioning the significant deficiencies of vitamin B12 or folic acid . It seems that macrocytic anemia may be often caused by vitamin B12 deficiency. Miligan et al.  conducted a test (Schilling test) where they found that vitamin B12 absorption was reduced in all the patients with chronic GVHD participating in their study. It is estimated that patients with end-stage kidney failure on hemodialysis lose 1–3 g of iron per year . It is caused by bleeding from uremic platelet dysfunction, blood entrapment in the dialysis machine, and impaired absorption of dietary iron. Oral iron is less effective than intravenous iron. Most patients with end-stage kidney disease receive ESAs, which increase erythropoietin and thus deplete the circulating iron concentration. Hemodialysis patients have low serum transferrin saturation and normal or high ferritin. However, it should be emphasized that a high serum ferritin level is not only typical of increased iron stores. Infections, inflammation, liver disease, and malignant tumors also affect ferritin levels . Additional causes of anemia after HSCT could be either latent viral infection reactivation or new viral infections acquired through blood transfusion. Graft vs. host disease and thrombotic microangiopathy might also contribute to the anemia after HSCT . It should be noted that isolated anemia can also be caused by drugs toxic to the bone marrow regardless of renal function . Moreover, the preparative regimen, graft source, and the presence of graft-versus-host disease (GVHD) influence the degree of myelosuppression and the time to hematopoietic recovery. In our population studied, in seven cases there was a history of CMV infection, in three cases there was a history of BKV infection in 44 cases a history of graft vs. host disease, and in one autoimmunohemolytic anemia with warm type antibodies. In our study, we examined 156 patients at least 100 days after HSCT due to various hematological diseases remaining under the care of the Department of Hematology, Transplantation, and Internal Diseases, Medical University of Warsaw, Poland. The study included only patients who survived HSCT and were discharged from the hospital. Ninety percent of patients underwent allogeneic HSCT from an unrelated donor, and 10% underwent allogeneic HSCT from a related donor. Mean creatinine was 1.12 mg/dl. 8.3% of patients had chronic kidney disease stage 3B, 14% for stage 3a. None of the patients had chronic kidney disease stage 4 or 5. The mean hemoglobin concentration was 13.2 g/dl, 26% of the population had diagnosed anemia (including 13% women, and 35% men). The mean MCV was 95.9 fl but it should be noted that 42% of the population had a macrocytic red cell. We had no data available on vitamin B2 and folic acid deficiencies. Additionally, we reviewed all the conditioning protocols, but none of them (myeloablative or nonmyeloablative, with and without total body irradiation including nephrotoxic drugs. They were mainly based on cyclophosphamide, etoposide, others were based on busulphan and cyclophosphamide, fludarabine and busulphan, busulphan and melphalan, etc. The prevalence of CKD in our population was 22. Prevalence of CKD after HSCT was reported in some studies . Three years after HSCT 2.2% of the survivors had CKD as reported by Rodrigues et al. , whereas in the study by Gutiérrez-García G et al.  the CKD prevalence in 161 living patients (out of 422 undergoing HSCT) was 10.2% at the last follow-up and in most, CKD developed 1 year after HSCT, independent of episodes of AKI. Sakaguchi et al.  found that 21.9% of patients after HSCT developed CKD. Recently, Zhou et al.  in a single-center series of 216 adult Asian patients with a long and complete follow-up reported a prevalence of 41 CKD of 19.0% at 25 years, whereas in a retrospective study of all 408 adult patients with allogenic HSCT by Pelletier et al.  the prevalence of CKD at 1 year was 19%. Higher prevalence of CKD ranging from 27% up to 34% were reported by Jo et al.  and Shimoi et al. . In the study of Touzot et al.  the prevalence of CKD in 123 allogeneic HSCT patients was 41%. In our study, we focused on the anemia prevalence in CKD population after HSCT. In none of the studies, data on the anemia prevalence in the CKD population were reported. Touzot et al.  reported that 18.5% of patients were referred to the Nephrology Department. At the time of referral, 14 (61%) had CKD and one had reached end-stage kidney disease. In our population, also one patient started hemodialysis due to biopsy-proven FSGS with nephrotic syndrome after HSCT due to acute myeloblastic anemia. As some patients with these severe hematological malignancies are cured with conventional chemotherapy without transplantation, the prevalence of chronic kidney disease in this population is variable and data are limited but data on the anemia prevalence are even more scarce. In the study by Travasso et al. , on 75 patients with hematological malignancies receiving antineoplastic treatment, the prevalence of renal disorders was 52.4% according to the CKD-EPI equation. After treatment of chronic myeloid leukemia with imatinib, CKD developed in 16% , whereas in other studies, CKD was diagnosed after therapy with tyrosine kinase inhibitors (imatinib, dasatinib, and nilotinib) in 22%, 5%, and 4% respectively and in 14% in the whole population . In chronic leukocytic leukemia leukemia, at the time of diagnosis prevalence of CKD was found to be 7.5% in the cohort of more than 2000 patients . As reported by Strati et al.  baseline CKD was observed in 10% of patients at the time of chronic leukocytic leukemia diagnosis, and a further 16% developed CKD after a median follow-up of 7 years, 2% required dialysis treatment. In patients with lymphoma, Desai et al.  reported that 14% had baseline CKD and 31% of patients developed CKD 10 years after lymphoma diagnosis. In patients with severe aplastic anemia, CKD prevalence was only 6% . As stressed by Sawinski  for a majority of patients, the exact etiology of CKD is never identified, but graft vs. host disease and thrombotic microangiopathy are important diagnoses to be considered. Therefore, it is important to stress that patients with CKD should be referred for nephrology evaluation not only to introduce and continue nephroprotection but also to look for other nephrology disorders requiring kidney biopsy and other management, drug nephrotoxicity or introduction of anemia therapy, including ESAs, HIF-PHIs, iron. However, we should be very cautious in starting ESAs in patients with a history of malignancy. In the recent paper from the KDIGO Controversy Conference on novel anemia therapies in chronic kidney disease, the conference participants agreed that no consistent signal is present across the HIF-PHIs of excess risk of malignancy-related adverse events. However, as in other nephrology trials patients with a history of recent or active malignancy were excluded. Moreover, the accrued exposure time in clinical trials and clinical practice has not been long enough to be confident of the absence of a clinically relevant risk compared with that for ESAs. It was also stated by conference participants that post-marketing surveillance would be important to confirm the safety of HIF-PHIs from the standpoint of cancer risk and to provide longer-term follow-up data. At present, it is recommended to avoid HIF-PHIs use in patients with a history of malignancy . As HSCT is the best curative treatment for severe and very severe aplastic anemia, as well as for some other nonmalignant conditions, the use of ESAs or eventually HIF-PHIs may be considered in patients with CKD and anemia after HSCT. We acknowledge limitations related to external validity and data availability being a single-center retrospective study. However, to the best of our knowledge, for the first time we focus on the anemia prevalence in the CKD population after HSCT. Concluding, anemia, is relatively common in CKD after HSCT. In both CKD and coexistent anemia, nephrology referral is to be taken into account to optimize therapy, including nephroprotection. 

