Specificity Information and Courses from MediaLab, Inc.

These are the MediaLab courses that cover Specificity and links to relevant pages within the course.

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Chemical Screening of Urine by Reagent Strip
Semi-automated and automated reagent strip readers:	View Page

CLIA Blood Banking Review
To detect the presence of blocking antibodies fixed on the red cells of a newborn infant:	View Page

CLIA General Laboratory Review
Which of the following best defines "specificity":	View Page
The term analytical specificity refers to:	View Page

Confirmatory and Secondary Urinalysis Screening Tests

Reasons for Performing Confirmatory or Secondary Macroscopic Urine Tests

Urine reagent strips are normally adequate for urine screening, but occasionally, it may be necessary to perform a secondary procedure to ensure the accuracy of the test result. Confirmatory or secondary procedures are usually performed for one or more of these reasons: To confirm a result that has been obtained on the reagent strip. To obtain a result from a highly pigmented urine that masks the result on the reagent strip. To test for a specific analyte (or analytes) that are not included in the specificity of the reagent strip test. For example, the glucose reagent strip test is specific for glucose, but you want to test for other reducing substances.

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Introduction to the ABO Blood Group System

"Immune" ABO Antibodies

A person exposed to a specific immunizing event may produce “immune” ABO antibodies of the same specificity as the “naturally” occurring antibody, but with different biological behavior. Such immunizing events include pregnancy with an ABO incompatible fetus or transfusion of ABO incompatible red cells. After immunization, the subject’s antibody may increase in titer and/or avidity, develop powerful hemolyzing properties, or become more active at 37ºC.

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Quality Control
Calculating Specificity A test's specificity measures the percentage of individuals without the condition being tested for, who will have a negative test. To calculate specificity, use the following formula: True Negatives (TN) Divided by True Negatives (TN) plus False Positives (FP) Times 100 or (TN ÷ (TN + FP)) x 100 The result is a percentage.	View Page
Specificity Example Let’s say that a company is developing a new testing procedure that has one-third the turn around time of the present “Tried and True” method. The company runs both methods on 1,000 individuals suspected of having the condition being tested for.	View Page
Specificity Example: Test Results In the pool of 1,000 tested individuals, 600 actually had the condition. The experimental method detected 875 positives, of which 275 were false. Of the 125 negatives detected by the experimental method, 25 were false.The tried and true method detected only 625 positives, 25 of them false. 375 negatives were found as well, of which 50 were false negatives.The experimental method detected far more positives, but a great number of these were false. The tried and true method, however, did generate more false negatives than the experimental method.	View Page
Specificity Example: Calculations (1) Determining the specificity of the experimental method will help show if the test is worthwhile.Using the equation for specificity, we insert the following numbers: 100 True Negatives Divided by (100 True Negatives + 275 False Positives) Times 100 or (100 ÷ (100 + 275)) x 100. The specificity for the “Experimental” method is 26.6%.	View Page
Specificity Example: Comparison We have determined that the specificity of our experimental method is approximately 27% and our tried-and-true method is almost 93%. Specificity reflects the ability of a test to categorize those individuals without the condition as negative. A highly specific test will be negative in most individuals without the condition. Conversely, those individuals who test positively with a highly specific test are likely to have the condition.	View Page
Specificity vs. Sensitivity To review, specificity is “disease focused”. The more specific a test is, the fewer false positive results will occur. Remember that a false positive result can possibly lead to a misdiagnosis with the possible consequence of unnecessary diagnostic procedures and therapies. Sensitivity, on the other hand, is “wellness or normal focused”. The more sensitive a test is, the fewer false negative results it produces.	View Page
Specificity Example: Calculations (2) To calculate the specificity of the tried-and-true method, we'll use these numbers: 325 True Negatives Divided by (325 True Negatives + 25 False Positives) Times 100 or (325 ÷ (325 + 25)) x 100. The specificity for the tried-and-true method is 92.8%.	View Page
Using the data and formula to the right, we can calculate specificity of the West Nile Virus test to be:	View Page
Based on the test results to the right, what is the specificity of this test?	View Page