**3. Blood loss in hemodialysis patients**

dothelial stores and intestinal iron absorption via hepcidin modulation; the relationship

American and European clinical practice guidelines (KDOQI-2006 and European Best Practice Guideline-2009) warned against regular iron administration when the ferritin concentration exceeds 500 µg/L, although the former guideline allowed clinicians to make a decision on IV iron administration above this level after carefully weighing up ESA responsiveness, hemo‐ globin and transferrin saturation, and the patient's clinical status [1, 9]. It is also worthy of note that the recent KDIGO-2012 guideline proposed a trial of IV iron in dialysis patients prior to ESA use, with the aims of sparing these expensive drugs and of reaching high TSAT (30%) and ferritin (500 µg/L) target values [10]; however, these new KDIGO target values for iron biomarkers were not fully endorsed by EDTA-ERA because of the potential risk of iron overload [11]. Likewise, the Japanese Society for Dialysis recently proposed that a minimal amount of IV iron (up to 650 mg in the induction phase) should be given to dialysis patients, and only in case of true iron deficiency (ferritin <100 µg/L), while also warning against

Iron stores in healthy humans average 3 to 4 g in men and 2.2 to 3.5 g in women [13, 14]. About 60% of iron is located within the hemoglobin protein of circulating erythrocytes and, to a lesser degree, in medullary erythrocytes; 20% of iron stores are located in the liver (hepatocytes and Kupffer cells) and in the reticulo-endothelial system (mainly in spleen macrophages), in the form of the iron-storage protein ferritin (marginally in haemosiderin) whereas muscle myoglobin accounts for about 10% of body iron [8, 13, 14]. Iron-containing enzymes represent only 1% of iron stores, while plasma transferrin-bound iron represents only a small fraction (0.2%=3 mg) of total body iron [13, 14]. Each day, macrophages of the reticulo-endothelial system recycle about 30 mg of iron from senescent erythrocytes, thus providing the 20-30 mg of iron required for normal erythropoïesis [8, 13, 14]. Physiological iron losses are estimated at about 1 mg/day (urinary loss: 0.1 mg/day; gut loss secondary to enterocyte desquamation: 0.6 mg/day; skin loss: 0.3 mg/day) but are increased in women by menstruation (the main cause of iron-deficiency anemia worldwide), pregnancy and breast-feeding [14]. Therefore, recom‐ mended daily dietary iron intake to compensate for iron losses is 10 mg/day generally (because of an absorption rate of only 10%) and 30 mg/day in pregnant women and nursing mothers [14]. Hepcidin-25, a hormone synthesized in the liver, is the master regulator of iron metabo‐ lism, acting negatively on both intestinal iron absorption and iron release from reticuloendothelial macrophages and liver cells by decreasing the expression of ferroportin, a protein that regulates iron export from these cells [8]. Hepcidin-25 synthesis is increased by iron itself and by inflammation (via IL6), and decreased by anemia, hypoxia, iron deficiency, haemor‐ rhage, erythropoïetin, and increased medullary erythropoïesis [8]. The mechanism by which this latter situation down-regulates hepcidin synthesis was recently linked to a new peptide hormone, erythroferrone, secreted by erythroblasts and acting directly on the liver [15]. Defective hepcidin-25 synthesis plays a paramount pathophysiological role in genetic hemo‐

between ferritin and iron stores may therefore be blunted or skewed [4, 8].

maintenance intravenous iron therapy because of the risk of iron toxicity [12].

**2. Normal iron metabolism**

58 Updates in Hemodialysis

With the ready availability of ESA and IV iron, iatrogenic blood losses, which are major contributors to iron deficiency in dialysis patients, have often been neglected. There are three distinct and cumulative sources of blood loss in this setting: 1) the dialytic technique itself; 2) regular blood sampling for patient monitoring, and 3) occult intestinal blood loss. Traditionally estimated to be between 4 and 12 liters/year, these blood losses classically represent 2 to 6 g of iron lost per year (1 L of blood contains about 500 mg of iron, although the value may be lower in dialysis patients because of a lower hematocrit) [17]. These classical approximations clearly overestimate dialysis-related blood loss. In addition, the type of vascular access and comor‐ bidities may strongly influence both the type and magnitude of blood loss.

Two recent publications have quantified blood loss associated with modern dialysis mem‐ branes at respectively 0.3 ml/session [18] and 0.9 ml/session [19], while blood-line losses have been calculated to be about 0.2 ml/session [18]. Thus, taking a value of 1.1 ml/session, annual blood losses due to conventional hemodialysis *per se* (3 sessions/week, 150 sessions/year) would be about 165 ml/year. But the major source of blood loss in dialysis units stems from the care of tunnelized double-lumen catheters, when nurses apply the universal protocol of purging 7 to 10 ml of blood in each branch at the outset of the hemodialysis session, leading to a yearly blood loss of 2.4 L, to which should be added 288 ml for routine monthly bacterial cultures of the anticoagulant locks. Thus, the total annual blood loss related to catheter care is about 2.68 L [20]. Use of a recent protocol proposed by Prof. Bernard Canaud, based on the purge of only 2 ml of blood instead of 7-10 ml/branch, would lessen catheter-related blood loss to only 888 ml/year, representing a net 77% reduction [20].

In a recent survey in France, blood samples for regular patient monitoring were quantified in 10 dialysis centers run by the healthcare provider Générale de Santé at between 350 ml and 450 ml/year [20], a volume close to the 368 ml found by Sargent and Acchiardo in patients dialysed at the University of Tennessee in Memphis in 2004 [17]. Note that blood sampling may be far more abundant in academic hospitals conducting clinical trials or pathophysiolog‐ ical studies.

The third source of blood losses in hemodialysis patients is the gut. These losses are occult, being below the detection limit of stool tests. They are favoured by uremic enteropathy and thrombopathy, anticoagulation of the extracorporeal circuit during dialysis sessions, and also antiplatelet and antivitamin K drugs [21, 22]. Rosenblatt and coworkers, in a study performed in the 1980s using chromium 51-labelled erythrocytes, quantified faecal blood loss at 0.83 ml/ day in healthy controls, 3.15 ml/day in non dialysis chronic kidney disease (CKD) patients and 6.27 ml/day (2.2 L/year) in hemodialysis patients [21]. These occult faecal blood losses are increased by antiplatelet and antivitamin K drugs: dialysis patients thus treated require higher IV iron dosages to replenish their iron stores (e.g 703 to 961 mg/year) [22, 23]. Thus, total blood losses in a hemodialysis patient with a native arteriovenous fistulae treated in a non academic center and not receiving antiplatelet or antivitamin K drugs can be estimated at 2.85 L/year (1.425 g of iron/year), whereas a patient with the same clinical profile but a double-lumen tunnelized catheter will lose 5.5 L/year (2.765 g of iron); note that both values are far lower than the classical estimates of 2 to 6 g/year [20].
