Specificity Information and Courses from MediaLab, Inc.

Immune antibodies occur in the serum of individuals who become sensitized to foreign antigens through pregnancy or transfusion. IgM predominates in the primary response, IgG in the secondary response. Most react at 37°C and are considered clinically significant. Examples include antibodies in the Kell, Rh, Duffy, and Kidd systems. Immune antibodies can be classified as alloantibodies or autoantibodies.Alloantibodies Produced by exposure to foreign red cell antigens which are non-self antigens but are of the same species. They react only with allogenic cells. Exposure occurs through pregnancy or transfusion. Examples include anti-K and anti-E. Autoantibodies Produced in an autoimmune process and directed against one's own red cell antigens. React with patient's own cells and all cells tested. Can possibly mask the presence of other significant antibodies. It is very important to make sure that no underlying significant antibodies are present if an autoantibody is suspected. A positive direct antiglobulin test (DAT) or auto control could indicate the presence of an autoantibody. Examples include cold auto (P or I) or warm auto (Rh specificity).

A molecular method may be the test method of choice for a variety of reasons, including the following: Organisms of interest, especially in microbiology or virology, may be extremely slow growing, fastidious or extremely limited in quantity. Other technologies lack the necessary sensitivity or specificity Patient population requirements

Hereditary hemochromatosis (HH) is frequently discovered only during management of associated illness or routine health evaluations. It has been estimated that only a small percentage of all affected persons are actually diagnosed. Individuals with HH may be symptomatic for several years prior to diagnosis and may have consulted multiple health care providers.Under-diagnosis of HH is thought to occur due to:• Lack of specificity of early signs and symptoms• Asymptomatic status of some patients until damage to organs and tissues has occurred• Confusion with liver disease due to other causes• Insufficient awareness and knowledge of HHEarly identification of persons with HH is essential to prevent serious and irreversible complications associated with severe iron overload. A classic triad of skin hyperpigmentation (bronzing), type 2 diabetes, and hepatic cirrhosis has long been recognized as evidence of advanced iron overload. However, persons with HH may present with a much wider variety of signs and symptoms, particularly if they are seen before significant iron accumulation has occurred. Age of presentation and disease severity are highly variable. A diagnosis of HH is based on laboratory evidence of iron overload, genetic mutations associated with HH, and presence of clinical signs and symptoms consistent with HH.(10)

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.

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.

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.

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.

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%.

Once an antibody has been identified and other clinically significant antibodies have been excluded, the case must be looked at as a whole to confirm the logical consistency of all results and data.This process includes assessing any inconsistencies.For example:1. Is the patient negative for the corresponding antigen? Yes: The patient is Jk(a-).2. Is the antibody specificity consistent with the typical phase(s) of reactivity for the antibody? Yes: Kidd antibodies are IgG and react in the antiglobulin phase.