There is no such thing as 100% sensitive serological test.

Based on the diction " sometimes serological tests fail to give real positive results" I suppose that these unexpected results could regard some patients whit clinical features of infection in progress who resulted negative for IgM or IgG avidity Alternatively I have to think that you observed some IgG negativity in previously IgG positive women. Under what conditions did you observe these false negativities?

Each lab method has its own sensitivity, specificity, -PV, +PV, & accuracy. Check the leaflet of the kit.

I'm sorry but I think in this case analytical specifications such as sensitivity, specificity, positive and negative predictive value cannot be evoked. Only the knowledge of the actual serological status of the patient or the comparison with other analyzers on the same samples can affirm that actually the results of the analytical system used (instrument + reagents) must be considered as false negatives. Lacking this information there is no answer to the question of Dr Hiba Riyadh Jameel

Nobody has corrected my false claim so I have to do it myself. Of course there are 100% sensitive tests, those that always give a positive reaction.

Without controversy: to calculate the diagnostic sensitivity (SE) of a test you need to know the "true" results: true positives (TP) and false negatives (FN) by using the formula SE = TP/(TP + FN)x100. So a test has a specificity of 100% if the FNs are equal to 0. The state of TP and FN can be asserted if you know the true serological state only. This last information is missing in the Dr Hiba question.

why Dr. Jukka Salminen ? please explain

becouse i read in some references about

serological tests fail to give positive real results in diagnosis

due to depended on antibodies

I mean sometimes serological tests fail to give positive real results (((( in diagnostic )))) because the antibodies appear in the body after several weeks from infection, or in some cases the host's body fails to form antibodies against this parasite . Antonio La Gioia Jukka Salminen i speak about the diagnostic in some cases

example :

If you have a fatal disease with no treatment (such as for early cases of AIDS), optimize specificity

If you are screening to prevent transmission of a preventable disease (such as screening for HIV in blood donors), optimize sensitivity

Sensitivity and specificity are functions of the screening test

if you use a given screening test on a low prevalence population, you will have a low positive predictive value and potentially many false positives

example 2

Suppose a patient exhibits symptoms that make her physician concerned that she may have a particular disease. The disease is relatively rare in this population, with a prevalence of 0.2% (meaning it affects 2 out of every 1,000 persons). The physician recommends a screening test that costs $250 and requires a blood sample. Before agreeing to the screening test, the patient wants to know what will be learned from the test, specifically she wants to know the probability of disease, given a positive test result, i.e., P(Disease | Screen Positive).

The physician reports that the screening test is widely used and has a reported sensitivity of 85%. In addition, the test comes back positive 8% of the time and negative 92% of the time.

The information that is available is as follows:

• P(Disease)=0.002, i.e., prevalence = 0.002
• P(Screen Positive | Disease)=0.85, i.e., the probability of screening positive, given the presence of disease is 85% (the sensitivity of the test), and
• P(Screen Positive)=0.08, i.e., the probability of screening positive overall is 8% or 0.08. We can now substitute the values into the above equation to compute the desired probability,

http://www.scientificamerican.com/article.cfm?id=what-is-bayess-theorem-an

So, Jukka Salminen Antonio La Gioia

Sensitivity, Specificity, PPV, NPV. A diagnostic test with 100% sensitivity can have maximum of 99% specificity, never 100%., as well as There is no test up till now to be sensitive &specific 100%. This is a bias. However, the molecular-based methods investigate the genetic material of any organism such as PCR the most recent method Real time PCR has a high sensitivity and specificity dependent on the DNA of the organism regardless of how low concentration or at that time was,,

Thank you for your opinion

Great discussion and apologize for the late reply Antonio La Gioia Jukka Salminen

I exclude that an immunocompetent subject does not produce antibodies against a parasite or a bacterium or a virus. This does not mean that the antibody response is always effective. Furthermore, I agree with the fact that the immune response may be delayed. This depends on many factors of both the parasite and the host. Therefore, if there are unambiguous clinical signs of disease or a history of a certain exposure, a negative result may be a "false" negative result since it is obtained in the "window period" of the infection. The poor quality of the diagnostic test can be evoked only if the negativity persists over time. The "window period" is the time from contact with the antigen to the appearance of the first IgM and depends, as already mentioned, on both characteristics of the infectious agent and the host.

Dear Hiba I agree with your observations on the specificity and sensitivity of a screening test. I disagree on your example 2 because the considerations made for a screening are not valid in the individual case of symptomatic patients for whom no screening test is to be used but diagnostic tests that, as you rightly pointed out, must Be more specific

thank you very much Dr. Antonio La Gioia

we used of Enzyme-Linked Immuno Sorbent Assay (ELIZA) for investigate of the parasite by depending on antibodys IgG and IgM, but sometimes serological tests fail to give positive real results, so we depending on molecular methods .

https://www.researchgate.net/profile/Shaban_A_A_Abdel-Raheem thank you