Diagnosis and treatment of pernicious anaemia

This guide aims to provide an evidence-based approach for the diagnosis and treatment of pernicious anaemia in general practice, and is intended to help general practice nurses in the management of patients with this condition in the absence of formal guidelines

Pernicious anaemia is one of the causes of vitamin B12 deficiency and is an autoimmune condition. Most patients have IgG autoantibodies targeted against gastric parietal cells and the B12 transport protein, Intrinsic Factor. The condition is more common in women, Northern Europeans and can be familial. They may have prematurely grey hair and blue eyes, have blood group A and may develop or have already developed other autoimmune disorders, including vitiligo, thyroid disease such as autoimmune thyroiditis and hypothyroidism and Addison’s disease.

Undiagnosed and untreated B12 deficiency can cause megaloblastic anaemia and irreversible damage to the central nervous system leading to paralysis and dementia. Pernicious anaemia is also associated with an increased risk of gastric cancer.

SYMPTOMS

• Gradual onset of features of anaemia, such as shortness of breath and tiredness
• Extreme tiredness, often described as a different type of tiredness or feeling tired even on waking from a good night’s sleep
• Lethargy
• Paraesthesia in the extremities, especially the feet.
• Muscle weakness
• Depression and low mood
• Problems with memory, understanding and judgment, often described as ‘brain fog’
• Difficulty in gait
• Visual disturbance.

DIAGNOSIS

The clinical picture is the most important factor in assessing the patient as there is no gold standard test to define B12 deficiency or diagnose pernicious anaemia.

Tests to identify B12 deficiency

FBC

This is the first line test, in particular mean corpuscular volume (MCV), which may show evidence of macrocytosis. However only 60% of patients with a B12 deficiency will have enlarged blood cells (megaloblastosis),1,2 and they can also be enlarged in alcohol abuse. If the patient also has an iron deficiency this will reduce the MCV so having both will effectively cancel each other out in regards to size of the MCV.

Serum B12

This test is widely available, of low cost and automated, but lacks both sensitivity and specificity.

There is disagreement about what level should determine deficiency. It has been proposed that a level of less than 200ng/l or 148pmol/l would have a sensitivity of diagnosing 97% of cobalamin deficiency.³ However serum cobalamin measures both the inactive (transcobalamin I and III) as well as the active (transcobalamin II). So patients could have symptoms at much higher levels.

Many clinicians feel this level is too low and identify patients with levels between 148pmol/l and 300pmol/l as having subclinical cobalamin deficiency, who – if symptomatic – require further investigation and a trial of therapy. A false normal cobalamin level can be caused by high levels of intrinsic factor antibody, so testing for this antibody would be advised in patients with clinical features such as megaloblastic anaemia or sub-acute combined degeneration of the spinal cord and an apparent normal cobalamin level.

The serum cobalamin level can be affected by many variables including diet, pregnancy, vitamin supplements, contraceptive pill and metformin.⁴

Red blood cell folate and serum folate

If the patient has been taking a folic acid supplement, for example, in pregnancy, then this will prevent the red blood cells from becoming enlarged. Therefore when suspecting a B12 deficiency, folate needs to be checked, to ensure correct interpretation of the FBC.

Healthy levels of folic acid are needed for the patient to convert the injectable B12 to biologically active B12, so any low levels would need correcting or the patient will have high serum B12 levels, but be unable to access them.

The following three tests are not commonly used in general practice and are not widely available. They are more likely to be requested in secondary care.

Plasma total Homocysteine (tHcy)

Deficiency of cobalamin results in elevated levels of plasma homocysteine (tHcy). Plasma tHcy is a sensitive marker of cobalamin deficiency and increases early in the course of the diseases and rises as the deficiency worsens. However, although sensitive, it is not specific and will also rise in folate deficiency, B6 deficiency, renal failure and hypothyroidism.

Also sample collection is difficult as it must be processed within 2 hours of collection and must be kept cool during that time.

Plasma methylmalonic acid (MMA)

Plasma MMA is raised in cobalamin deficiency. Again the test is sensitive, but not specific and is a high cost test, so is not routinely used in the UK.

Holo transcobalamin (HoloTC)

HoloTC is the active fraction of plasma cobalamin, hence it is more sensitive and specific than serum cobalamin. Its use has not yet been fully evaluated in routine use, but may be used as a first line test in the future.

Tests for identifying pernicious anaemia versus other causes of vitamin B12 deficiency

Intrinsic factor antibody

Intrinsic factor antibody is positive in 40-60% of cases,5 so the finding of a negative intrinsic factor antibody assay doesn’t rule out pernicious anaemia. The positivity rate increases with age,3 and in Latino-Americans and African-Americans.⁶

Intrinsic factor antibody levels are vulnerable to false positive results if a recent cobalamin injection has been administered.⁴

Parietal Cell Antibodies

Parietal cell antibodies test positive in 80% of patients with pernicious anaemia, but are also positive in 10% of normal people, so a positive test is not definitive.⁷

DIAGNOSIS RECOMMENDATIONS

The clinical picture is the most significant factor in diagnosis.

Patients should have a FBC, TFT, U&E, B12, folate and glucose, and all patients with anaemia, neuropathy or glossitis and suspected of having pernicious anaemia should be also tested for intrinsic factor regardless of cobalamin levels.⁴

If patients already have one of the autoimmune diseases linked with pernicious anaemia or a family history of the condition, then diagnosis of pernicious anaemia is more likely. Negative results may require further investigation or referral to haematology.

TREATMENT

All patients diagnosed with pernicious anaemia will need life long therapy with replacement B12. The BNF8 recommends treatment with hydroxocobalamin intramuscular injections. Treatment frequency depends on whether the patient has neurological symptoms or not.

Without neurological symptoms

Hydroxocobalamin 1000 micrograms IM, three times a week for two weeks, followed by lifelong two-to-three monthly injections.

With neurological symptoms

Hydroxocobalamin 1000micrograms IM alternate days until there is no further improvement, reviewing after three weeks to assess progress and possible side effects, but can be administered for up to 2 years.

Patients with severe anaemia may develop a transient hypokalaemia, the significance of which is not known.⁹

Any folate or iron deficiencies will also need to be treated. There is some controversy over whether B12 levels should be normalised prior to treating folate deficiency as there is a theoretical increased risk of subacute degeneration of the cord, also known as Lichtheim’s disease, in which there is loss of myelin in the dorsal and lateral columns of the spinal cord, although the mechanism remains unclear.

Side effects

Hydroxocobalamin is generally well tolerated. Side effects include itching, rash, chills, fever, hot flushes, dizziness and rarely, anaphylaxis.

Maintenance therapy

Patients with pernicious anaemia require lifelong treatment. Alternatives to hydroxocobalamin injections are available, including high dose oral tablets, nasal sprays, sub-lingual preparations and subcutaneous methylcobalamin injections and although there is some limited research on oral therapy for general B12 deficiency, it is not conclusive and most of the other preparations have not been thoroughly researched for either their effectiveness or safety profile. High dose oral cobalamin of 1000-2000mg daily may be a reasonable alternative to those patients who cannot tolerate IM injections, provided there is good compliance.¹⁰ Most patients prefer injection therapy to ensure effective treatment.

It is important to point out that many patients will not have effective control at the recommended 3 monthly intervals and will experience a return of their symptoms, and so will require maintenance injections at more frequent intervals. There is a lack of consensus regarding the frequency how often patients truly need maintenance injections, especially in the UK. Many other countries, such as France and Spain, routinely give monthly injections, usually of cyancobalamin, which in the UK has been completely replaced by hydroxocobalamin as the drug of choice.⁸ In 1967 Tudhope et al,11 compared serum concentrations of cyancobalamin with hydroxocobalamin and found hydroxocobalamin lasted twice as long, but they found great variations between patients. They stated that ‘variation between patients makes it impossible to anticipate the duration of effect of a single injection of one of these drugs in a single patient’. They also found that ‘following injections of cyancobalamin and hydroxocobalamin, most of the excretion occurred in the first 24 hours; with hydroxocobalamin the excretion was less than cyancobalamin.’

We have to look to other countries to find reassurance if we are to provide effective treatment to all patients with pernicious anaemia.

The Dutch National Health Council12 report of 2003 does not determine a safe upper intake level of B12 replacement, echoing the findings of expert commissions from the American Institute of Medicine and the Scientific Committees for Human Food from the European Union, who had reported 3 years earlier that toxicity from high levels of vitamin B12 poses no real danger.

In 2009, the Regional Disciplinary Medical Board in Eindhoven stated clearly that an overdose is not possible: ‘There can be no question of an overdose of hydroxocobalamin, as [any] excess is excreted in urine by the kidneys and therefore can not accumulate in the body.’13

In 1999 in Japan, kidney dialysis patients received 0.5mg methylcobalamin 3 times a week IV for 6 months. Due to the lack of renal clearance serum levels rose to an average of 54,000pmol/l without adverse effects.¹⁴

There is no evidence that more frequent injections causes harm, but plenty of evidence, some of it anecdotal, that undertreatment does cause harm. Not only will a patient’s quality of life be affected, but they also risk irreversible neurological damage, dementia and death.

TREATMENT RECOMMENDATION

In conclusion some patients will be well controlled with 3 monthly injections, but many others will require more frequent treatment. This will not cause the patient harm and will need to be adjusted depending on the patients own individual response to treatment

REVIEW

It is the general practice nurse who will administer the majority of injections, making her ideally placed to monitor the patients response to therapy and liaise with the GP should there be any need to increase the frequency of injections. All patients should have their FBC and reticulocytes checked after 8 weeks to monitor progress and all patients should have yearly blood tests to check FBC and TFT. Testing of B12 levels is not required and inappropriate as following injections the serum level of B12 rises regardless of therapeutic effectiveness,15 and serum B12 does not distinguish between the active and inactive forms of cobalamin, so cannot be used to judge effective treatment. The presence or absence of symptoms is the only way to assess whether treatment is effective.

The practice nurse should also always be alert to any mention of gastric symptoms and ensure timely referral to the GP due to the higher risk of gastric cancer.

• While the advice and information in this guide is believed to be true and accurate at the time of writing, it can only be used as guidance. There is a lack of research into pernicious anaemia, including its diagnosis, treatment and long term prognosis.

REFERENCES

1. Beck WS. Neuropsychiatric consequences of cobalamin deficiency. Advanced Institute of Medicine 1991;36:33-56

2. Lindenbaum J, Heaton EB et al. Neuropsychiatric disorders caused by cobalamin deficiency in the absence of anaemia or macrocytosis. New England Journal of Medicine 1988; 318:1720-1728

3. Carmel R, Sarrai M. Diagnosis and management of clinical and subclinical cobalamin deficiency: advances and controversies. Curr Hematol Rep 2006;5:23-33

4. Devalia V, Hamilton M, Molloy A, on behalf of the British Committee for Standards in Haematology. Guidelines for the diagnosis and treatment of cobalamin and folate disorders, Br J Haematol 2014;166(4):496-513

5. Ungar B, Whittingham S, Francis CM. Pernicious Anaemia: incidence and significance of circulating antibodies to Intrinsic Factor and to Parietal Cells. Austr Ann Med 1967;16:226-229

6. Carmel R. Reassessment of the relative prevalence of antibodies to gastric parietal call and to intrinsic factor in patients with Pernicious Anaemia; influence of patient age and race. Clin Exp Immunology 1992;89:74-77

7. Khan S, Del-Duca C, Fenton E, et al. Limited value of testing for intrinsic factor antibodies with negative gastric parietal cell antibodies in pernicious anaemia. J Clin Pathol 2009;62:439-441

8. BNF. Drugs used in megaloblastic anaemias. March 2017. https://www.evidence.nhs.uk/formulary/bnf/current/9-nutrition-and-blood/91-anaemias-and-some-other-blood-disorders/912-drugs-used-in-megaloblastic-anaemias

9. Carmel R. Treatment of severe pernicious Anaemia: No Association with sudden death. Am J Clinical Nutrition. 1988;48:1443-1444

10. Stabler SP. Clinical Practice: Vitamin B12 Deficiency. N Engl J Med 2013;368:149-160

11. Tudhope GR, Swann HT, Spray GH. Patient variation in pernicious anaemia, as shown in a clinical trial of cyanocobalamin, hydroxocobalamin and cyancobalamin-zinc tannate. Br J Haematol 1967;13(2):216-228

12. Dutch National Council. Nutritional Standards: vitamin B6, folic acid, vitamin B12. The Hague: Health Council of the Netherlands, 2003;2003/04. https://www.gezondheidsraad.nl/en/task-and-procedure/areas-of-activity/healthy-nutrition/dietary-reference-intakes-vitamin-b6-folic

13. Regional Disciplinary Medical Board Eindhoven verdict, Uitspraak 15 April 2009 nr. 113b June 2011 (in Dutch).

14. Kuwabara S, Nakazawa R, Azuma N, et al. Intravenous Methylcobalamin Treatment for Uremic and Diabeteic Neuropathy in Chronic Hemodialysis Patients. Intern Med 1999;38(6):427-75.

15. Carmel R. How I treat cobalamin (vitamin b12) deficiency. Blood 2008;112:2214-21