Wednesday, January 24, 2018

H pylori diagnosis: FAQs

Here are some key points from a recent review.

Who should be tested?

Any one with PUD, past or active.

Any patient with MALT lymphoma.

Here are some additional recommendations from the ACG guidelines:

All patients with active peptic ulcer disease (PUD), a past history of PUD (unless previous cure of H. pylori infection has been documented), low-grade gastric mucosa-associated lymphoid tissue (MALT) lymphoma, or a history of endoscopic resection of early gastric cancer (EGC) should be tested for H. pylori infection…

Patients initiating chronic treatment with a non-steroidal anti-inflammatory drug (NSAID) should be tested for H. pylori infection (strong recommendation, moderate quality of evidence)...

When upper endoscopy is undertaken in patients with dyspepsia, gastric biopsies should be taken to evaluate for H. pylori infection…

Patients with unexplained iron deficiency (ID) anemia despite an appropriate evaluation should be tested for H. pylori infection.

The guideline makes these additional statements regarding patients who should be considered for testing (softer recommendation):

In patients with uninvestigated dyspepsia who are under the age of 60 years and without alarm features, non-endoscopic testing for H. pylori infection is a consideration…

In patients taking long-term low-dose aspirin, testing for H. pylori infection could be considered to reduce the risk of ulcer bleeding…

Adults with idiopathic thrombocytopenic purpura (ITP) should be tested for H. pylori infection. Those who test positive should be offered eradication therapy (conditional recommendation, very low quality of evidence).

How should testing be carried out?

If an EGD is not being done, from the review:

Helicobacter pylori infection can be diagnosed using noninvasive and invasive methods. In general, both noninvasive and invasive tests are equally accurate.13 Noninvasive tests include the urea breath test, fecal antigen test, and serologic test. The preferred noninvasive tests in the outpatient setting are the urea breath test and fecal antigen test given their excellent accuracy and ability to diagnose active infection. The fecal antigen test relies on identifying H pylori antigens in the stool using an enzymatic immunoassay.13 In the urea breath test, urea labeled with 13C or 14C is given to patients. Urease, if present, converts urea into ammonia and labeled CO2 that is exhaled, indicating a positive result.13 Before testing, proton pump inhibitors (PPIs) and antibiotics should be discontinued at least 2 and 4 weeks, respectively, as these can interfere with the urea test.10 Pretreatment sensitivity and specificity of both these tests are approximately 95%.13 Although the cost of testing varies by location and laboratory, the estimated cost of the urea breath test and fecal antigen test is $102.80 and $19.70, respectively.14 Serologic testing is not recommended to detect active infection, as it cannot distinguish between active disease and previous exposure. Antibodies to H pylori can remain elevated for a long time even after treatment, potentially increasing the number of false-positive results.13 The 1 positive aspect of serologic testing is that it is the only test for H pylori that is not affected by PPI therapy, antibiotics, or by the presence of blood in the stomach.

If EDG done, again from the review:

Invasive testing strategies require upper endoscopy and include the biopsy urease (campylobacter-like organism) test, histologic assessment, and culture. The biopsy urease test is a good first-line test, as it is accurate, rapid, and inexpensive. This test relies on H pylori urease to convert urea into ammonia, increase the pH, and change the color of the pH indicator.15 Although the specificity is excellent with this test (greater than 95%), the sensitivity can vary from 75% to 98%.15 The urease test is preferred in patients without recent use of PPIs and antibiotics, as outlined above.10 However, in patients with recent PPI or antibiotic use, histologic assessment of biopsy samples is the better choice, although these medications can interfere with bacterial density.

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