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認識腎性貧血 Understanding Renal Anemia
1. 鐵質缺乏 (Iron deficiency)。
2. 葉酸(Folic acid)及維他命缺乏。
3. 營養不良 (Malnutrition)。
4. 影響EPO治療效果不佳的原因包含：尿毒素增高、鐵質缺乏、感染/發炎、慢性血液流失、葉酸或維他命B12缺乏、營養不良等。都有可能影響身體對EPO 的效果。
Anemia in Chronic Kidney Disease
In patients with chronic kidney disease, normochromic normocytic anemia mainly develops from decreased renal synthesis of erythropoietin. The anemia becomes more severe as the GFR (glomerular filtration rate) progressively decreases. No reticulocyte response occurs, red blood cell survival is decreased, and there is an associated increased bleeding tendency due to uraemia-induced platelet dysfunction.
Iron deficiency is also common in patients with chronic kidney disease. The iron deficiency may be absolute, often due to poor dietary intake or sometimes occult bleeding, or functional, when there is an imbalance between the iron requirements of the erythroid marrow and the actual iron supply. Iron deficiency leads to a reduction in formation of red cell haemoglobin, causing hypochromic microcytic anaemia. Other causes for anaemia in chronic kidney disease include the presence of uraemic inhibitors (eg parathyroid hormone, inflammatory cytokines), reduced half-life of circulating blood cells, and deficiencies of folate or vitamin B12.
● Studies of patients with chronic kidney disease (CKD) have shown that the prevalence of anaemia (defined as a haemoglobin level less than 12 g/dL in men and postmenopausal women and less than 11 g/dL in premenopausal women) is about 12%.
● The National Health and Nutrition Examination Survey (NHANES) III study showed that the prevalence of anaemia increases as eGFR falls (1% at eGFR 60, 9% at 30 and 33% at eGFR 15 ml/min/1.73 m2).
● In patients with chronic renal failure, patients with diabetes are at a greater risk of developing anaemia earlier in the course of their disease (associated with inappropriately low levels of erythropoietin). Comparing patients with similar eGFR and erythropoietin levels, those with type 2 diabetes are generally more anemic.
● Often diagnosed by routine review blood tests.
● Renal anaemia may lead to the onset or aggravation of lethargy, cold intolerance and loss of stamina.
● Anemia increases cardiac output, therefore contributing to the development of left ventricular hypertrophy and dilatation.
Look after your kidneys
Causes of anemia in patients with chronic kidney disease (CKD), other than renal failure itself, include:
● Chronic blood loss
● Iron deficiency
● Vitamin B12 or folate deficiency
● Chronic infection or inflammation
● Aluminium toxicity
● Bone marrow infiltration
● Pure red cell aplasia
Investigate patients with chronic kidney disease (CKD) if their haemoglobin falls to 11 g/dL or less, or they get symptoms due to anaemia, such as tiredness or breathlessness.
This will involve ruling out other causes of anaemia, assessment of renal function, assessment of any cardiovascular and other complications of anaemia or chronic kidney disease.
● Renal function, eGFR and electrolytes.
● FBC, blood film, iron studies (ferritin, transferrin saturation, iron), B12 and folate. Where ferritin <100 μg/L there is iron-deficiency anaemia. If ferritin is above this level, a functional iron deficiency (and hence a requirement for iron supplementation) is defined by the percentage of hypochromic red cells >6% (if test is available) or otherwise a transferrin saturation <20%.
● Other investigations will be determined by likely alternative diagnoses and cardiovascular effects of anaemia, eg thyroid function tests, renal ultrasound, echocardiography, investigations for gastrointestinal bleeding.
● Any patient with chronic kidney disease presenting with anemia:
● Should be referred to the local specialist renal department for full assessment and management. Clinical assessment should include an assessment of nutrition, general wellbeing and other possible causes for anaemia (eg occult blood loss).
● Blood pressure should also be checked and any other factor suggesting acute on chronic renal failure, eg infection.
● The basic blood test investigations as outlined above should be sent (ensuring the results are available at the renal department).
● Management of anemia should be considered in people with anaemia of chronic kidney disease (CKD) when the haemoglobin level is less than or equal to 11 g/dL (or 10 g/dL if under 2 years of age).
● In people with anemia of CKD, treatment should aim to maintain stable haemoglobin levels between 10 and 12 g/dL for adults and children aged over 2 years, and between 9.5 and 11.5 g/dL in children aged under 2 years.
● Treatment with erythropoiesis-stimulating agents should be offered to patients with anemia of CKD who are likely to benefit in terms of quality of life and physical function. There is no evidence to distinguish between erythropoiesis-stimulating agents in terms of efficacy.
● The time taken for erythropoetin treatment to be effective will depend on individual patient factors, such as degree of anemia, degree of renal failure and presence of other adverse factors, eg iron deficiency.
● Contra-indications for erythropoetin treatment include uncontrolled hypertension.
● Potential side-effects of erythropoetin include increase in blood pressure or aggravation of hypertension, headache, increase in platelet count, influenza-like symptoms (may be reduced if intravenous injection given over 5 minutes), thromboembolic events, pure red cell aplasia, hyperkalaemia, and skin reactions.
There have been very rare reports of pure red cell aplasia in patients treated with epoetin alfa. The Commission on Human Medicines has advised that in patients developing epoetin alfa failure with a diagnosis of pure red cell aplasia, treatment with epoetin alfa must be discontinued and testing for erythropoietin antibodies considered. Patients who develop pure red cell aplasia should not be switched to another erythropoietin.
● Monitoring: in people with anemia of CKD, hemoglobin should be monitored: •Every 2-4 weeks in the induction phase of erythropoiesis-stimulating agent therapy.
● Every 1-3 months in the maintenance phase of erythropoiesis-stimulating agent therapy.
● More actively after dose adjustment of the erythropoiesis-stimulating agent.
● Epoetin alfa: ● Epoetin (recombinant human erythropoietin) is used for the anemia associated with erythropoietin deficiency in chronic renal failure. The clinical efficacy of epoetin alfa and epoetin beta is similar.
● It is also used to increase the yield of autologous blood in normal individuals and to shorten the period of anaemia in patients receiving cytotoxic chemotherapy.
● Epoetin beta is also used for the prevention of anaemia in preterm neonates of low birthweight.
● Darbepoetin: ● Is a hyperglycosylated derivative of epoetin which has a longer half-life and may be administered less frequently than epoetin.
● Other factors which contribute to the anemia of chronic renal failure, eg iron or folate deficiency, should be corrected before treatment and monitored during therapy.
● Aluminium toxicity, concurrent infection or other inflammatory disease may impair the response to erythropoietin.
● People receiving erythropoiesis-stimulating agent maintenance therapy should be given iron supplements (often requires intravenous iron) to keep their: ● Serum ferritin between 200 and 500 μg/L, and either:
● The transferrin saturation level above 20% (unless ferritin >800 μg/L); or
● Percentage hypochromic red cells less than 6% (unless ferritin >800 μg/L).
● Clinically relevant hyperparathyroidism should be treated in order to improve anaemia management in patients with anaemia of CKD.
● Where possible, blood transfusions should be avoided in patients in whom kidney transplant is a treatment option.
● Anemia is an adverse indicator for the progression of chronic kidney disease. Therefore, correcting anaemia is considered an important part of slowing or even stopping the progression of chronic kidney disease.
● Treatment with recombinant human erythropoietin in pre-dialysis patients corrects anemia, avoids the requirement for blood transfusions and also improves quality of life and exercise capacity.
Restricting the progression of chronic kidney disease, eg smoking cessation, optimal control of diabetes.