How to Critically Appraise A Diagnostic Article

Sandy De Groote

Clinical Situation

A doctor comes to you. She has a 21 year old male patient she suspects has an ulcer and wants to do a test for H. pylori infection. She has heard of a new stool antigen test that she hopes will be less invasive and less expensive than other tests. The doctor wants to know more about this test.

PICO

P: Young adult with possible H Pylori I: How accurate is stool antigen test C: In comparison with other tests O: Diagnosis H. Pylori Infection

Search

PubMed Clinical Queries (diagnosis, specificity) – Helicobacter pylori AND stool antigen AND

non-invasive

The Article Selected

Diagnosis of Helicobacter Pylori infection with a new non-invasive antigen-based assay

Lancet 1999; 354:30-33

Methods Design: Prospective Setting: Multicentre study (11) in Europe Patients: 501 (276 male, 255 women); Age range 17-

88 years; Undergoing gastroscopy at endoscopy Description of diagnostic tests: Presence of H. Pylori

was invasively confirmed if histology (antrum, corpus, or both) and urease test were positive, or if culture was positive. (Gold Standard – proven method)

Presence of H. Pylori was non-invasively confirmed if antigens were found in stool samples using the HpSA (Meridian Diagnostics) (new diagnostic test)

Patients classified as having H Pylori infection received an eradication regimen; 107 were reassessed 4 weeks after therapy

Issues of Validity

Was there an independent, blind comparison with a reference (“gold”) standard of diagnosis? – Yes

Was the diagnostic test evaluated in an appropriate spectrum of patients? Yes

Was the reference standard applied regardless of the diagnostic test result? Yes

Results

Look at results in paper– -examined urea breath test– Stool antigen test (what we will examine)– Table 1 (pg 31)

Use 2X2 Diagnostic Test Calculator found at ebm.peds.uic.edu

Crunch in the numbers – various approaches

Applicability

Stool antigen tests could be used reliably to diagnosis H.pylori