Diagnostic Tests I

A urine culture is the "gold standard" test for urinary tract infection (UTI). Unfortunately, cultures take about 24 hours for results and it would be desirable to have a quicker test in order to start treatment immediately.

An "enhanced" urinalysis (EU) has been developed for the early detection of UTI in febrile children less than 2 years old withou an obvious focus of infection. In the study that evaluated this test, 102 children with UTI were evaluated. A positive UA was defined as > 10 WBC/mm3 + bacteria on gram stain. 91 of the children had a positive EU using this criterion. 2079 children with negative urine cultures (no UTI) were evaluated, and 2067 of them also had negative EU results.

Based on these data, answer the questions below. You may find the online diagnostic test calculator helpful.

  1. What is the sensitivity of the EU test? (e.g. 0.99)
  2. What is the specificity of the EU test? (e.g. 0.99)
  3. What is the probability that a child with a positive EU really has UTI? (e.g. 0.99)
  4. What is the prevalence of UTI in the study sample? (e.g. 0.10)
  5. What is the likelihood ratio for a positive EU test? (e.g. 4)
  6. What is the likelihood ratio for a negative EU test? (e.g. .1)