Anaemia

Approach to anaemias.

This is relatively straightforward – if the Hb is low the patient is anaemic. Then look at the mean corpuscular volume (MCV) and the red cell distribution width (RDW). If the MCV is low, the patient probably has an iron deficiency anaemia. If the MCV is high, consider a megaloblastic anaemia or haemolysis. If the MCV is normal, look at the RDW. If this is normal, the patient probably has an anaemia of chronic disorder. If the RDW is raised, consider a mixed picture.

Perspective – red cell distribution width

The RDW gives an indication of whether the MCV reflects an average from a relatively uniform cell population, or is reflecting a cell population more divergent in volume. It is calculated in two different ways, as either the RDW-CV (coefficient of variation, or standard deviation divided by MCV, which is then expressed as a percentage) or RDW-SD which is the width of the frequency distribution curve taken at a frequency of 20%). The RDW-CV, being a ratio, is susceptible to influence by the MCV itself, with low values pushing up the result)¹. Both the RDW, and its newer cousin the change in RDW over time, are of interest as markers of prognosis in cerebrovascular diseases, possibly in some malignancies² and in an array of other conditions.³

Depending on the starting haemoglobin concentration and the amount transfused, it will also change with blood transfusion, as do several other indices useful in determining the cause of an anaemia, such as the serum folate, and, transiently for 24 hours, the serum iron, although ferritin, haptoglobin, LDH and vitamin B12 levels are hardly affected.)⁴

Making sense of a peripheral smear

The various names given to individual findings on the peripheral smear sometimes seem a bit arcane, but really don’t say anything very mysterious – try correlating with the (simplified) table below (note that most of the terms apply to red cells (RBCs) but that some apply to neutrophils):

Perspective – measuring reticulocytes

About 1/120^th of the red cell mass has to be replaced each day, so about 0.5-2.0% of the circulating red cells are reticulocytes: the normal reticulocyte count is thus 0.5% to 2%. The corrected reticulocyte count compensates for anaemia by correcting to a haematocrit of 0.45. (corrected = measured retic count x (pt’s HCT/0.45))

The production index compensates for the ‘shift’ reticulocytes, which are large cells released prematurely from marrow in response to anaemia. The correction factor is based on the estimated number of days that these cells take to mature in the blood stream. Maturation time (days) is 1 for HCT of 0.45, 1.5 if 0.35, 2 if 0.25, and 2.5 if HCT is 0.15.

RPI = [(% retics) X (PCV)]/(maturation time X 0.45)

i.e. RPI = corrected retic count divided by maturation time.

The RPI will thus be > 2 or 3 in setting of normal marrow response to blood loss, and will be <1 when there is marrow failure. A high RPI will be found if there is bleeding or haemolysis with a functioning marrow. If an absolute reticulocyte count is available (normal range 0.05 to 0.1 x 10¹²/L) then this obviates the need for a haematocrit correction, and measures of mRNA density may also help with maturation time. Note that reticulocytes may continue to mature in vitro at room temperature.

Although worth looking at, evidence on RPI diagnostic accuracy in differentiating between the various causes of pancytopenia is not particularly heartening, particularly in the context of dual deficiency anaemias.⁵

Megaloblastic anaemias

B12 and folate deficiencies are discussed in detail in the section on nutrition. Megaloblastosis refers to the a condition of reduced DNA synthesis which manifests as maturation slowing or arrest at a marrow level – the peripheral blood manifestations of this are macrocytosis (raised MCV) and the presence of right shifted (hypersegmented) polymorphs.

Other causes of macrocytosis include:

• Marrow disorders such as myelodysplastic syndromes, aplastic anaemia, leukaemias.
• Drugs and toxins – alcohol, colchicine, co-trimoxazole, hydroxyurea, metformin, methotrexate, phenytoin, sulphasalazine and certain ARVs – e.g. zidovudine, stavudine and lamivudine. (Abacavir and tenofovir or not likely to be causes.)
• Lab artefact – when several RBCs are stuck together, the machine reads them as one.
• Miscellaneous – hypothyroidism, haemorrhage and haemolysis.

Normochromic and microcytic anaemias 

The simplest overall measure of iron deficiency (suspected in the setting of a microcytic anaemia) is the serum ferritin. For some reason (perhaps the number of studies available) many clinical epidemiology texts focus on this test as an example of cut-point choice influencing test performance.⁶ with a value of less than 15 micromol/l having a sensitivity of 59% (spec 99%, LR+ 51.8, LR- 0.4) whereas a value of 25 has a sensitivity of 22% (spec 96%, LR+ 4.8, LR- 0.8.)

It is important to remember that the management of iron deficiency is NOT about simply replacing iron – the critical issue is to determine why the deficiency occurred in the first place, so that a repeat event can be prevented. Common causes are:

• Heavy menses
• Occult GIT bleeding due to non-steroidal anti-inflammatory use
• Heavy worm infestations are listed as a cause, but are more of a problem in children.
• Dietary deficiencies in poor societies are commonest when the diet consists largely of starch and tea.

Remember that anaemias secondary to a chronic disorder usually are associated with a raised ferritin and should not generally be treated with iron. The Hb is usually higher than 7g%, so before ascribing an anaemia of much less than this value to the anaemia of chronic disorder, look for another cause, such as iron or B12 deficiency.)

Perspective – can iron be harmful in iron replete patients with chronic illness anaemia?

Iron supplementation is not necessarily beneficial in this group, and there has been a continuous trickle of studies and reviews addressing this issue over the years.⁷ In particular, the situation in HIV positive patients raises some concerns.⁸ Trying to correct the anaemia associated with tuberculosis by giving iron is becoming increasingly unlikely to be sensible; hepcidin is both a regulator of iron metabolism and an important component of the body’s immune response to TB.⁹ Fixing the TB is the best way of fixing the anaemia.

Pragmatically, ferrous sulphate tablets cause gastritis in many people, and in those with borderline nutrition, generating unnecessary anorexia is enough of a reason to avoid the practice, even without hypothetical concerns about infection susceptibility thresholds being changed. Don’t give iron to everyone who is anaemic – check MCV first (and ferritin if still in doubt) and look for a reasonable predisposing cause. (An exception to the general non-replacement trend is CRF patients also on erythropoietin.)¹⁰

Leukoerythroblastic anaemias

This refers to the finding of immature cells from the red and white cell lines in the peripheral smear. Causes:

• Marrow stimulation – infection, hypoxia, even trauma.
• Infiltration (malignancy, myelofibrosis)
• Megaloblastic anaemias secondary to B12 or folate deficiency.

Management – look for and treat the cause. After pulling blood for B12 and folate levels, it is not unreasonable to treat for nutritional megaloblastic anaemia while awaiting further results. A marrow is often helpful if the diagnosis isn’t obvious from physical examination and CXR and other radiology directed at identifying bony metastases or myeloma.

Sideroblastic anaemia

This is rare but can be puzzling – it is one of the causes of a hypochromic microcytic anaemia with a normal or high ferritin. The bone marrow show iron stores are adequate to excessive, and there are ring sideroblasts (early RBCs with a ring of mitochondrial iron around the nucleus). Associated with alcohol, malignancies, and the use of INH and pyrazinamide. Pyridoxine 25 mg per day may be of some benefit.

Haemolytic anaemia

In the presence of anaemia and a raised MCV, consider haemolysis particularly if the LDH is high and there seems to be evidence of free haemoglobin – increased unconjugated bilirubin, presence of ‘blood’ on urinary dipsticks. Do smear and check serum haptoglobin (will be low). Urinary haemosiderin may be seen with special staining. Causes are either immune (+ve Coombs) or due to RBC trauma (damage in transit across a prosthetic valve, microangiopathic anaemia, DIC, etc. Hereditary membrane disorders (e.g. spherocytosis) present every now and again – check by asking the laboratory to investigate for osmotic fragility. Overall, look for the cause and treat that.

HIV associated autoimmune haemolytic anaemia is quite striking, and responds to ARVs. Short term use of high dose corticosteroids may be helpful in all haemolytic anaemia, including HIV associated: prednisone 1mg/kg/day. Once Hb >10, wean slowly, and consider stopping completely when Hb stable and LDH normal. Don’t forget about drug associated haemolytic anaemia (cephalosporins, penicillins, quinolones, NSAIDs, rifampicin, sulphonamides and sulphonylureas, phenytoin, lansoprazole, and efavirenz. Possibly even paracetamol.)

Microangiopathic haemolytic anaemia

This is due to damage to red cells within the blood vessels – marked fragmentation is seen on the peripheral smear. Causal associations are with DIC (septicaemia, disseminated malignancies, pre-eclampsia, and TTP) and with arteritis (acute glomerulonephritis, renal cortical necrosis, polyarteritis nodosa, Wegener’s, SLE). Microthrombi in vessels may also be responsible (haemolytic uraemic syndrome, homograft rejection). Management is to identify and, if possible, treat the cause. The differential is particularly vexing during or immediately following pregnancy:¹¹

(APLS: antiphospholipid syndrome; AFLP: acute fatty liver of pregnancy; HUS: haemolytic-uraemic syndrome; TTP: thrombotic thrombocytopenic purpura, PET: pre-eclampsia)

Aplastic anaemia.

Background

Aplastic anaemia is a life threatening illness with a poor prognosis if untreated. The ideal therapeutic option is bone marrow transplantation ¹² from an HLA compatible sibling. This gives a 75-95% chance of long-term survival. If there is no available donor (the patient’s relatives are HLA incompatible) then there are two remaining options: do nothing except transfuse as required, or give antithymocyte globulin.

Perspective – anti-thymocyte globulin in aplastic anaemia

RCTs in this field are rare. A prospective cohort study published in 2003¹³used a combination of ATG 40 mg/kg/d for 4 days, 10 mg/kg/day of cyclosporine for 6 months and 1 mg/kg/day of methylprednisolone for 2 weeks. A 60% response rate to transfusion independence was obtained which was sustained at one year. Response was relatively prompt – a platelet count of 50 at 3 months predicted a 90% chance of surviving 5 years. A placebo controlled RCT from 1983,¹⁴ which was a partial cross-over design involving 42 patients, showed a 52% response rate to transfusion independence in the treated group, and a 0% response in the untreated group. (p=0.0005).

Several others studies of even weaker design (cohorts with or without historical controls) are available. For instance Paquette et al ¹⁵ demonstrated a 6 year survival of 49% (CI 45 – 53%), and Agarwal et al¹⁶ demonstrated a 48.6% response to one course of ATG. An earlier study¹⁷ of 150 patients demonstrated 31% transfusion independence at 3 months.

Number needed to treat – ATG.

The baseline comparator across reported studies is heterogeneous, probably reflecting different referral patterns, selection criteria, and quality of supportive care. Using a mortality rate of 90% in untreated patients with severe aplastic anaemia, ATG probably yields a 30-70% response rate; hence absolute risk reduction is from 20 to 60%. NNT thus 2 – 5.

Giving ATG

Ideally this should be done in a high care situation where close monitoring is possible. One regimen is as follows:

• ATG 40 mg/kg/d for four days (i.e. the total dose required is 160 mg/kg, or about 9.6g for a 60 kg patient). Give as an infusion of 4 hours, slowing to 6 hours if reactions develop. Premedication with an antihistamine and an opiate may be helpful.
• Corticosteroids – methylprednisolone 500 mg/day for four days
• Thereafter start prednisone 0.5 mg/kg for one month.
• If patient adherence can be assured, the addition of cyclosporin 10 mg/kg/d plus ketoconazole 50mg per day, with cyclosporin level monitoring and appropriate dosage adjustment.

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2. Hu L, Li M, Ding Y, Pu L, Liu J, Xie J, Cabanero M, Li J, Xiang R, Xiong S. Prognostic value of RDW in cancers: a systematic review and meta-analysis. Oncotarget. 2017 Feb 28;8(9):16027-16035. doi: 10.18632/oncotarget.13784. PMID: 27926498; PMCID: PMC5362543. ↩

3. Salvagno GL, Sanchis-Gomar F, Picanza A, Lippi G. Red blood cell distribution width: A simple parameter with multiple clinical applications. Crit Rev Clin Lab Sci. 2015;52(2):86–105. doi: 10.3109/10408363.2014.992064. ↩

4. Berz D, Singh H, McCormack E, Mazur E. Modification of anaemia parameters after blood transfusion. Blood 2006;108(11): 966. https://doi.org/10.1182/blood.V108.11.966.966 Poster. ↩

5. Das J, Khonglah Y, Tiewsoh I, Chowdhury Z, Barman H. Utility of reticulocyte indices in the diagnosis of pancytopenia. J Family Med Prim Care. 2022 Apr;11(4):1335-1340. doi: 10.4103/jfmpc.jfmpc_1121_21. Epub 2022 Mar 18. PMID: 35516681; PMCID: PMC9067176. ↩

6. Sackett DL, Haynes RB, Guyatt GH, et al. Clinical epidemiology. A basic science for clinical medicine. Little, Brown and Co. 1991. p 130 ↩

7. Oppenheimer SJ, Macfarlane SB, Moody JB, et al. Effect of iron prophylaxis on morbidity due to infectious disease: report on clinical studies in Papua New Guinea. Trans R Soc Trop Med Hyg. 1986;80:596-602 ↩

8. Clark TD, Semba RD. Iron supplementation during human immunodeficiency virus infection: a double-edged sword? Med Hypotheses. 2001;57:476-9 ↩

9. Kererkhoff AD, Meintjes G, Burton R, et al. Relationship Between Blood Concentrations of Hepcidin and Anemia Severity, Mycobacterial Burden, and Mortality Among Patients With HIV-Associated Tuberculosis.  J Inf Dis 2016;213:61–70 DOI: 10.1093/infdis/jiv364 ↩

10. Weiss G, Goodnough LT. Anaemia of chronic disease. NEJM. 2005;352:1011-23 ↩

11. Adapted from Scully M, Hunt BJ, Benjamin S, et al. Guidelines on the diagnosis and management of thrombotic thrombocytopenic purpura and other thrombotic microangiopathies. Br J Haematol. 2012 doi:10.1111/j.1365-2141.2012.09167.x ↩

12. Marsh JC, Gordon-Smith EC.  Treatment options in severe aplastic anaemia. Lancet. 1998:351:1830-31 ↩

13. Rosenfeld S, Follmann D, Nunez O, et al. Antithymocyte globulin and cyclosporine for severe aplastic anaemia. JAMA. 2003;289:1130-5 ↩

14. Champlin R, Ho W, Gale RP. Antithymocyte globulin treatment in patients with aplastic anaemia. N Engl J Med. 1983;308:113-8 ↩

15. Paquette RL, Tebyani N, Frane M, et al. Long-term outcome of aplastic anaemia in adults treated with anti-thymocyte globulin: comparison with bone marrow transplantation. Blood. 1995;85:283-90 ↩

16. Agarwal MB, Agarwal Um, Bhave AB, et al. Anti-thymocyte globulin therapy in acquired aplastic anaemia. J Assoc Physicians India. 1993;41:371-3 ↩

17. Young N, Griffith P, Brittain E, et al. A multicentre trial of antithymocyte globulin in aplastic anaemia and related disease. Blood. 1988;72:1861-9 ↩

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