The Lateral Flow Test has been used in developing countries

The Lateral Flow Test has been used in developing countries as a low cost way to diagnose patients with human immunodeficiency virus (HIV). The Lateral Flow Test is more cost effective and portable than the gold standard assessment. The validity of this test was assessed in 1176 patients by comparing the screening result with a gold standard procedure, the enzyme-linked immunosorbent assays (ELISAs). The results are displayed in the table below.

Table. Comparison of Test Results: Lateral Flow Test vs. Gold Standard ELISA

Gold Standard Assessment of HIV Status with Enzyme-Linked Immunosorbent Assays (ELISAs)

Lateral Flow Test

HIV Diagnosis

No HIV Diagnosis

Total

HIV Positive Screening Result

323

17

340

HIV Negative Screening Result

178

658

836

Total

501

675

1176

Calculate the sensitivity & specificity of the Lateral Flow screening test. (3)

Calculate the false positive and false negative rates. Which one would worry you the most in practice and why? (4)

What is the probability of having the disease (as evidenced by the gold standard test) if a patient screens positive for HIV with the Lateral Flow screening test? What is this type of probability called? (3)

Solution

Sensitivity is the probability that a test will indicate \'disease\' among those with the disease:

Specificity is the fraction of those without disease who will have a negative test result:

therefore according to the data a ,b,c,d are 323,17,178,658 respectively.

so according to the formula sensitivity will be 0.025

specificity = 0.355

b)false positive will be 17

false negative will be 178

c) probability will be 327/340 = 0.96 , this is called definite probability