What are the steps for performing an automated hemoglobin determination?

Hemoglobin

Hemoglobin concentration is regulated by a renal sensing mechanism that operates to maintain a balance between oxygen supply and oxygen requirement of renal tissues. A decrease in concentration or arterial oxygen saturation of hemoglobin or any increase in hemoglobin affinity for oxygen causes increased erythropoietin production through increased expression of hypoxia-inducible factor.2 The effect of erythropoietin on bone marrow is usually limited by available iron, so red blood cell production is stimulated to approximately twice its basal value of 1% of the total red blood cell mass per day. Consequently, red blood cell mass increases slowly in response to hypoxia.3 Because it increases blood viscosity, a higher hemoglobin concentration at the same total blood volume reduces blood flow, offsetting the increase in oxygen delivery. Normal cardiac output is reestablished by a proportionate increase in plasma volume (i.e., by an increase in total blood volume).4 The affinity of hemoglobin for oxygen, in association with blood flow distribution, translates oxygen flow into oxygen availability. This characteristic of hemoglobin is classically depicted in the oxygen dissociation curve (oxygen equilibrium curve). Because of its remarkable ability to combine reversibly with large quantities of oxygen, hemoglobin increases the oxygen transport capacity of blood approximately 70-fold over that of oxygen transported dissolved in plasma. For example, if the entire oxygen requirement of the maternal organism had to be met by physically dissolved oxygen, the required cardiac output would be 100 L/minute.

Anaemia174,175

Haemoglobin concentrations tend to be maintained until the GFR falls below 30 mL/min. At this time anaemia ensues. There are several reasons for the anaemia of chronic renal failure. Perhaps the most important is the failing kidney's inability to produce sufficient quantities of erythropoietin, the hormone that drives the bone marrow to produce red blood cells. Other factors, such as reduced red cell survival are also important. In addition, the uraemic environment renders the bone marrow relatively resistant to the action of erythropoietin, especially if inflammation and infection are present. Recombinant human erythropoietin is now readily available but at considerable cost. Careful monitoring of anaemia is also required so that treatment can begin early. The use of subcutaneous recombinant human erythropoietin on a regular basis can be initiated in order to achieve a haemoglobin level of 11 g/L. Normalization of haemoglobin should be avoided as this increases mortality. Adequate utilizable iron is required to minimize erythropoietin dosage and many centres in the West now administer regular intravenous iron to dialysis patients.

9.08.4.2 Hemoglobin and Erythropoietin

Hemoglobin concentration is one of the major factors influencing the delivery of oxygen to tumors. It is, therefore, not surprising that low hemoglobin concentration is, in general, a poor prognostic factor in cancer patients. In a review of 51 studies involving 17 272 patients, the prognostic relationship between hemoglobin concentration and local tumor control was analyzed. Of these, 39 studies (14 482 patients) showed a correlation, while only 12 (2790 patients) did not (Grau and Overgaard, 1998). More recent data from the Danish head and neck cancer (DAHANCA) 5 and 7 trials (Hoff, 2012; Hoff et al., 2011a,b) concluded likewise that pretreatment hemoglobin was prognostic for outcome, but that transfusion prior to and during treatment did not improve outcome. These observations indicate that the relationship between anemia and tumor hypoxia is complex. There is evidence that tumor hypoxia is redundantly influenced by structural and metabolic differences between normal tissues and solid tumors that contribute to development and maintenance of tumor hypoxia (Grogan et al., 1999; Hirst, 1986; Vaupel, 2004; Vaupel et al., 1989, 2006). In fact, pretreatment tumor oxygenation measured by electrodes and pretreatment plasma hemoglobin did not correlate by linear regression, rather by quadratic regression as low hemoglobin correlated with low median tumor pO2 and high hemoglobin likewise related with low median tumor pO2. This finding was consistent in head and neck cancer (Becker et al., 2000; Clavo et al., 2003; Nordsmark et al., 2005), carcinoma of the uterine cervix (Fyles et al., 2000; Nordsmark et al., 2006), breast, and uterine cervix and vulva (Vaupel et al., 2002, 2006). In outcome analysis in head and neck, hemoglobin was a prognostic marker for survival, and independent of tumor hypoxia in multivariate analysis. This comparison was performed based on pretreatment measurements, which may not be the optimal timing. However, measurements of tumor oxygenation before and after transfusion in 19 uterine cervix cancers showed a statistically significant improvement in tumor oxygenation after transfusion in half of the cases only (Sundfor et al., 1997).

The potential benefit of increasing hemoglobin by blood transfusion prior to radiotherapy has been investigated in a number of studies (Thomas, 2002). The first clinical investigation of this approach was in advanced squamous cell carcinoma of the uterine cervix (Evans and Bergsjø, 1965). Transfusion to patients with low hemoglobin level resulted in an increased tumor oxygen tension, as measured superficially in the tumor using first generation oxygen-consuming electrodes. The same study was also the first to show that transfusion to a hemoglobin level of 11 g dl− 1 or higher was significantly related to improved survival. A Canadian retrospective study of 605 cervix cancer patients showed that the negative influence of low hemoglobin on prognosis could be overcome by transfusion (Grogan et al., 1999). However, these observations were not supported by data from a prospective phase III trial, from the DAHANCA study group, which showed no benefit of transfusion in patients with low hemoglobin levels (Hoff, 2012; Hoff et al., 2011a,b).

The concentration of hemoglobin can also be increased by stimulation with the hormone erythropoietin (EPO). Preclinical studies have shown that anemia in animals could be corrected by serial injection with EPO and that this EPO treatment also overcame the anemia-induced radiation resistance (Stuben et al., 2003; Thews et al., 1998). The concept of using EPO to correct for anemia was tested in a number of clinical trials, and although low hemoglobin can be effectively and safely improved by EPO (Hoskin et al., 2009b; Lavey and Dempsey, 1993), a number of studies in patients undergoing treatment for head and neck cancer failed to show any benefit (Henke et al., 2003; Hoskin et al., 2009b; Machtay et al., 2007; Overgaard et al., 2007). In fact those patients that actually received EPO during radiation therapy did significantly worse than those patients that did not receive EPO and as a result all EPO and radiation trials have been stopped.

Alternative ‘hemoglobin-related’ methods for improving tumor oxygenation include the use of perfluorocarbons (Rockwell, 1985), which are small particles capable of carrying more oxygen than hemoglobin, or manipulation of the oxygen-unloading capacity of blood by modifying the oxy-hemoglobin dissociation curve. This can be achieved either by increasing the red blood cell 2,3-DPG content (Siemann and Macler, 1986), 2,3-DPG being one of the most important allosteric factors controlling the hemoglobin–oxygen dissociation curve, or by using antilipidemic drugs (Hirst and Wood, 1991). Although each of these approaches has been shown to improve the oxygenation status of experimental tumors and/or enhance radiation damage, none of them have yet reached controlled clinical testing, thus their potential usefulness in the clinic is uncertain.

Anaemia

Haemoglobin concentrations tend to be maintained until the GFR falls below 30 mL/min. There are several reasons for the anaemia of CKD. Perhaps the most important is the failing kidney's inability to produce sufficient quantities of erythropoietin, the hormone that drives the bone marrow to produce red blood cells. Other factors such as reduced red cell survival are also important. Recombinant human erythropoietin is now readily available but at considerable cost and there is evidence that it improves the quality of life. However, using erythropoietin to target higher levels of haemoglobin has now been shown to increase the risks of hypertension, stroke, vascular access thrombosis and probably the risk of death and progression to renal failure.235 In patients with CKD stages 3 and 4, normalization of haemoglobin did not reduce the risk of cardiovascular events.236 In the CHOIR study, patients randomized to a target haemoglobin of 13.5 g/dL had a significantly higher risk of cardiovascular events than patients randomized to a target haemoglobin of 11.3 g/dL with no improvement in the quality of life.237 Finally, the TREAT trial of darbepoetin alfa in patients with diabetes mellitus and CKD reported that as compared with placebo darbepoetin alfa did not reduce the risk of either of the two composite end-points of either death or a cardiovascular event or death or a renal event but was associated with an increased risk of stroke.238 Erythropoietin should be considered in patients with chronic kidney disease who are symptomatic or who have haemoglobin of <9 g/dL. Other causes of anaemia such as blood loss, iron folate and B12 deficiency should be sought for and treated. The European Best Practice Guidelines now suggest a target haemoglobin of 10–12 g/dL in patients with CKD.239 Adequate utilizable iron is required to minimize erythropoietin dosage and many centres in the West now administer regular intravenous iron to dialysis patients.

39 What are the current indications for ESA use in chemotherapy-induced anemia?

An Hb concentration that is approaching or falling below 10 g/dL. In patients with a higher risk of vascular events (elderly; those with uncontrolled hypertension, limited cardiopulmonary reserve, or underlying coronary artery disease; frail patients), watchful waiting is recommended until the Hb < 10 g/dL. ESAs should be used cautiously in patients at a high risk for venous thromboembolism such as those with pancreatic and stomach cancer, thrombocytosis, leukocytosis, and morbid obesity. ESAs should only be used in patients receiving palliative chemotherapy and not in adjuvant chemotherapy.

Rizzo JD, Somerfield MR, Hagerty KL, et al: Use of epoetin and darbopoetin in patients with cancer: 2007 American Society of Hematology/American Society of Clinical Oncology clinical practice guideline update, Blood 111:25–41, 2008.

Khorana AA, Kuderer NM, Culakova E, et al: Development and validation of a predictive model for chemotherapy associated thrombosis, Blood 111:4902–4907, 2008.

When to transfuse

Adequate hemoglobin concentration is essential for oxygen delivery. However, transfusion is associated with a number of risks in the critically ill, including increased rates of infection, thromboembolism, and death. Whilst a restrictive transfusion threshold of 7 g/dL is widely regarded as safe in most critically ill patients (Hebert et al., 1999), including those after cardiac surgery (Hajjar et al., 2010), there have been concerns that this level may be insufficient for those patients with TBI where oxygen delivery may be critical.

Outcome differences have not been demonstrated between restrictive and liberal transfusion strategies after TBI in randomized controlled trials (McIntyre et al., 2006; Robertson et al., 2014) and liberal transfusion has been associated with increased incidence of adverse events (Robertson et al., 2014). Observational studies have also signaled that transfusion may be associated with worse long-term outcome (Warner et al., 2010; Elterman et al., 2013; Leal-Noval et al., 2016). There is also some evidence to suggest that higher transfusion thresholds of 10 g/dL may predispose to progression or development of intracerebral hematomas (Vedantam et al., 2016), implicating a mechanism involving microvascular damage from transfused blood.

At the same time, higher hemoglobin concentrations are associated with improved cardiovascular stability. Furthermore, there is evidence for a detrimental influence of anemia on cerebral oxygenation. Transfusion acutely improves brain tissue oxygenation (Smith et al., 2005; Zygun et al., 2009), although this does not have a measurable effect on cerebral metabolism (Zygun et al., 2009). Increased rates of brain tissue hypoxia have been detected with transfusion thresholds of 7 g/dL compared to 10 g/dL (Yamal et al., 2015), and this was associated with an increased risk of early death, but a reduced risk of late death.

Given the lack of definitive evidence, a reasonable approach would be to individualize transfusion thresholds according to the prevailing physiology as measured by multimodality monitoring.

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