Several serological developers report PPA and NPA values for several patient collection time intervals, with better performance on samples collected later after the onset of symptoms. Antibodies are estimated to form 10 to 14 days after infection, peak at about 28 days and then remain in circulation for months. Therefore, this index expresses the probability that a given test result will be expected in a patient with a particular disease in relation to the likelihood that the same result will occur in a patient in the absence of the disease. For example, positive CT LR scan scan for acute appendicitis (94% sensitivity and 95% specificity) is considered to be about 18.8 euros; This suggests that a person is about 19 times more likely to have a CT scan if they have acute appendicitis than if they do not have acute appendicitis. For example, a positive scan in a patient with clinical signs and symptoms suggesting acute appendicitis indicates a very high probability (each LR> 10 is considered to be a high probability that the diagnosis is correct). On the other hand, LR is – for CT scanner in case of acute appendicitis 0.06, indicating that there is a minimum probability that the disease will be present if the test is negative. For ultrasound (USG) at the diagnosis of acute appendicitis (sensitivity 86% and specificity 81%) LR and LR values are 4.5 and 0.17, respectively. Note that the decision to order a test is also based on the first assessment of the probability of the disease in question and the extent of a normal or normal disease. For example, a CT scanner might have a good LR for decision in (or out) appendicitis in a child with abdominal pain, but if the doctor thinks the child has simple abdominal colic and appendicitis is very unlikely, CT should not be controlled given the cost and exposure to radiation.
Therefore, it is a more prudent option to start with ultrasound and receive TDD only if the results remain uncertain or if the patient does not improve. The question of the prior probability of a disease and its contribution to final clinical interpretation in combination with LR information deserves a full discussion that we will leave for the future. An example is the microbiological smear of the larynx used in patients with sore throats. Usually, publications that indicate the APA of a larynx indicate the likelihood that this bacterium is present in the throat instead of being infected with the bacteria found. If the presence of this bacterium has always resulted in sore throats, then the APP would be very helpful. However, bacteria can colonize individuals in a harmless manner and never cause infection or disease. The sore throat that occurs in these people is caused by other medications such as a virus. In this situation, the gold standard used in the evaluation study represents only the presence of bacteria (which could be harmless), but no bacterial caustic sore throats. It can be shown that this problem influences positive predictive value much more than negative predictive value.  To evaluate diagnostic tests in which the gold standard examines only the possible causes of the disease, an extension of the predictive value called etiological predictive value can be used.   Although sometimes synonymous is used, a positive predictive value generally refers to what is determined by the control groups, while a probability after the test refers to a probability for a person. However, if the probability of pre-testing of the person`s target condition is the same as the prevalence in the control group used to determine the positive forecast value, both are numerically identical.
Abbreviations: ROC, characteristic of the receiver`s operation; AUC, an area below the ROC curve; IC, confidence interval; LRTI, lower respiratory tract infection; NPA, negative approval rate; NPV, negative predictive value; AAE, positive percentage agreement; The APA, positive forecast value; ROC, the operating characteristic of the receiver; RPD, retrospective medical diagnosis; SIRS, systemic inflammatory reaction syndrome Infrequent, only one part of the pre-reference area