{"id":166,"date":"2020-11-29T12:52:57","date_gmt":"2020-11-29T18:52:57","guid":{"rendered":"https:\/\/betterpathology.com\/?p=166"},"modified":"2022-09-17T16:01:22","modified_gmt":"2022-09-17T21:01:22","slug":"sensitivity-and-specificity","status":"publish","type":"post","link":"https:\/\/betterpathology.com\/?p=166","title":{"rendered":"Sensitivity and Specificity"},"content":{"rendered":"\n

We want tests that are highly sensitive and highly specific for the condition being tested, but that is not always possible.\u00a0\u00a0Often, we must sacrifice one for the other.\u00a0\u00a0Simply stated, negative results can be trusted when there is high sensitivity, and positive results can be trusted when there is high specificity.\u00a0\u00a0So, we have to ask: is it better not to miss negatives or positives?\u00a0\u00a0<\/p>\n\n\n\n

There is not usually a neat separation between healthy patients and patients with disease.  Instead, patient populations exist in overlapping distributions, which can be illustrated as follows:<\/p>\n\n\n\n

\"\"<\/figure><\/div>\n\n\n\n

The vertical blue line represents the cutoff between positive and negative test results.  In this illustration, the cutoff is placed in a compromise position between the two populations, creating a group of false negatives (FN) and false positives (FP).  <\/p>\n\n\n\n

\"Diagram\n\nDescription<\/figure><\/div>\n\n\n\n

If a test is highly sensitive<\/em><\/strong>, the cutoff is shifted to the left, eliminating false negative results, but increasing the number of false positive results.<\/p>\n\n\n\n

\"Diagram\n\nDescription<\/figure><\/div>\n\n\n\n

If a test is highly specific<\/em><\/strong>, the cutoff is shifted to the right, eliminating false positive results, but increasing the number of false negatives.  As we have discussed previously, this is the situation with antigen tests<\/a> for SARS-CoV-2. <\/p>\n\n\n\n

When screening large populations for disease, it is important not to miss possible positives, so we choose a test that highly sensitive.  We do not want any false negatives.  False positives can be sorted out later; this is just a screen after all.  On the other hand, it is important that confirmatory tests have high specificity.  When we are confirming disease in a population selected by a screen, we want to eliminate false positives.<\/p>\n\n\n\n

If the goal of testing for SARS-CoV-2 is to avoid false negative results, favor sensitivity over specificity.  But this trade-off is not necessary with all test systems.  PCR tests<\/a> increase sensitivity by amplification and increase specificity with detection probes unique to the virus.  The result is a separation between populations, increasing specificity and sensitivity at the same time:<\/p>\n\n\n\n

\"Diagram\n\nDescription<\/figure><\/div>\n\n\n\n

Are sensitivity and specificity the only considerations when evaluating a test?  No, it is more complicated, but I am sure you guessed that.  We will talk about other measures of test systems and the results they produce next time.<\/p>\n","protected":false},"excerpt":{"rendered":"

We want tests that are highly sensitive and highly specific for the condition being tested, but that is not always possible.\u00a0\u00a0Often, we must sacrifice one for the other.\u00a0\u00a0Simply stated, negative results can be trusted when there is high sensitivity, and positive results can be trusted when there is high specificity.\u00a0\u00a0So, we have to ask: is […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[12,5,4],"tags":[],"class_list":["post-166","post","type-post","status-publish","format-standard","hentry","category-12","category-statistics","category-testing"],"jetpack_publicize_connections":[],"jetpack_likes_enabled":true,"jetpack_sharing_enabled":true,"jetpack-related-posts":[{"id":150,"url":"https:\/\/betterpathology.com\/?p=150","url_meta":{"origin":166,"position":0},"title":"Choosing Tests","author":"Kevin Homer, MD","date":"November 28, 2020","format":false,"excerpt":"The limits of my language mean the limits of my world.-Ludwig Wittgenstein, 1918. Throughout the pandemic of 2020, the vocabulary of laboratory medicine has been used indiscriminately and imprecisely, resulting in muddled communication and poor decisions.\u00a0\u00a0Today we will discuss basic terms used to evaluate laboratory tests so that you can\u2026","rel":"","context":"In "2020"","block_context":{"text":"2020","link":"https:\/\/betterpathology.com\/?cat=12"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/betterpathology.com\/wp-content\/uploads\/2020\/11\/SARS-CoV-2-Result-vs-Infection-matrix.png?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":180,"url":"https:\/\/betterpathology.com\/?p=180","url_meta":{"origin":166,"position":1},"title":"Accuracy, Precision and Predictive Value","author":"Kevin Homer, MD","date":"December 2, 2020","format":false,"excerpt":"We want accurate tests, don\u2019t we?\u00a0\u00a0By that, don\u2019t we mean that we want precise test results?\u00a0\u00a0Well, not exactly.\u00a0\u00a0Before we leave the subject of laboratory statistics, there are a few more words we need to learn. Accuracy\u00a0is the ability of a test to aim for the target.\u00a0\u00a0Visually, accuracy looks like this:\u2026","rel":"","context":"In "2020"","block_context":{"text":"2020","link":"https:\/\/betterpathology.com\/?cat=12"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/betterpathology.com\/wp-content\/uploads\/2020\/11\/Target-accurate-imprecise.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/betterpathology.com\/wp-content\/uploads\/2020\/11\/Target-accurate-imprecise.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/betterpathology.com\/wp-content\/uploads\/2020\/11\/Target-accurate-imprecise.png?resize=525%2C300&ssl=1 1.5x"},"classes":[]},{"id":110,"url":"https:\/\/betterpathology.com\/?p=110","url_meta":{"origin":166,"position":2},"title":"Antigen Tests","author":"Kevin Homer, MD","date":"November 14, 2020","format":false,"excerpt":"Elon Musk\u00a0recently tweeted that he was tested four times in the same day.\u00a0\u00a0Two tests were positive, and two tests were negative.\u00a0\u00a0How can this be?\u00a0 Mr. Musk was tested with the\u00a0BD Veritor\u00a0Plus rapid antigen test for SARS-CoV-2.\u00a0\u00a0BD Veritor is one of several SARS-CoV-2\u00a0antigen tests\u00a0made available in the United States by an\u2026","rel":"","context":"In "2020"","block_context":{"text":"2020","link":"https:\/\/betterpathology.com\/?cat=12"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":132,"url":"https:\/\/betterpathology.com\/?p=132","url_meta":{"origin":166,"position":3},"title":"Antibody Tests","author":"Kevin Homer, MD","date":"November 22, 2020","format":false,"excerpt":"There is no test for\u00a0COVID-19.\u00a0\u00a0Instead, testing focuses on detection of SARS-CoV-2, the virus known to cause COVID-19 or the body\u2019s response to infection.\u00a0\u00a0Today we will discuss antibody tests, the blood tests used to detect past infections. 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