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Little GEMs - How hot are you on H. pylori and coeliac disease?

Test your knowledge for the nMRCGP with this little GEM from the GPnotebook

Test your knowledge for the nMRCGP with this little GEM from the GPnotebook

Helicobacter pylori (formerly named Campylobacter pylori) is a gram negative S shaped or spiral bacillus, described as a Unipolar flagellate, 1 by 3 micrometres in size. It is a microaerophilic, and produces urease and other toxins. Infection with Helicobacter pylori is common in patients with peptic ulceration.

Question:

With respect to testing for H. pylori:

• which tests can be used both pre- and post-eradication treatment to determine presence of H. pylori?

• can serological testing be employed post-eradication treatment?

Answer:

The presence of H. pylori may be confirmed by:

• microscopy for characteristic rod bacilli

• culture of H. pylori on selective media

• "urea breath test" - production of radiolabelled CO2 from swallowed urea - the most accurate test for H pylori (1)

• stool antigen test

• serology

o antibodies to urease - this method cannot be used for judging eradication because antibody titres fall slowly

o some kits provide a rapid result while the patient waits ("near patient test"). Laboratory based tests with a high sensitivity are useful but much less accurate (specific) than other methods. Near patient blood tests are less accurate still and are not recommended (1)

• gastric biopsy

• assay for anti-H. pylori IgG antibodies in saliva

A review of H pylori testing suggested that (2):

• both the 13C-urea breath and stool antigen tests are accurate methods for testing for H. pylori after eradication therapy

• serological tests are of no value in confirming successful eradication, as the antibody persists long after successful eradication

• C-urea breath tests and stool antigen tests are generally more accurate than serological tests and they can be used both pre- and post-treatment

Reference:

1. BSG (2002). Dyspepsia management guidelines.

2. Drug and Therapeutics Bulletin 2004; 42(9):71-2.

Investigation for Coeliac Disease

Three different antibodies are often used in the diagnostic work-up for possible coeliac disease (antigliadin antibody, anti-endomysial, anti-transglutaminase antibody).

Question: with respect to these different antibody tests?

• which two antibody tests are the most specific?

• is immunological testing sufficient to make the diagnosis of coeliac disease

Answer:

Antibodies to components of cereals are common in the serum of patients with coeliac disease.

The sensitivity and specificity of serology in patients with suspected coeliac disease are:

Anti-gliadin antibody test:

• sensitivity: 75-95%

• specificity: 80-95%

Anti-endomysial antibody test

• sensitivity: >= 90%

• specificity: >= 97%

transglutaminase antibody test

• sensitivity: >= 90%

• specificity: >= 97%

The presently available serological tests cannot substitute for a diagnostic biopsy.

Question:

What other blood test findings might be present if a patient has possible coeliac disease?

Answer:

Haematology:

• blood film - usually dominated by effects of iron deficiency, such as hypochromia, anisocytosis - despite co-existing folate deficiency; Howell-Jolly bodies indicate splenic atrophy

• mean cell volume is often low - see above

• clotting studies may show prolonged prothrombin time from vitamin K deficiency

Biochemistry:

• liver function - hypoalbuminaemia in severely ill patients

• ferritin – often reduced

• vitamin D, calcium may be reduced

This series is based on GPnotebook Education Models (GEMs) - the full version is available via GPnotebook Plus, a service free to UK medics. Register at www.gpnotebook.co.uk

The urea breath test is the most accurate for H.pylori H-pylori

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