Is it normal to have a negative disease screening result

In most cases, a negative disease screening result is normal, which means that the test did not detect positive indicators related to the screened disease, and can temporarily rule out the risk of infection or incidence of related diseases. This is the result that everyone wants to get when doing screening.

But don’t just ignore it when you see a negative result. Clinically, there are indeed a few special cases where “negative results are not normal”, the most common of which is false negatives. Not long ago, I met a girl in the outpatient clinic who came to be tested for HIV because she had had unprotected high-risk sexual contact. The first screening result was negative. She was happy to leave. I asked about the exposure time and found out that it had only been 2 weeks. It happened to be during the window period of HIV infection. The antibody concentration in the body had not yet reached the threshold that can be detected by the screening reagent. I hurriedly asked her to come back for a retest when she was 4 weeks or 6 weeks old. After the 6-week retest was still negative, the infection was truly ruled out.

In addition to the window period, if the lesion is not taken during sampling, the detection reagent is not sensitive enough, and the subject has recently taken drugs that affect the test results, it may lead to a situation where there is clearly a problem but the screening shows a negative result. There was a heavy smoker who had been smoking for 30 years. Every year, the low-dose CT lung cancer screening showed negative results. But last year, he suddenly coughed with blood. After a contrast-enhanced CT, it was found that he had central lung cancer. When he looked back at the previous low-dose CT film, he found that the lesion was just blocked by the ribs, so the diagnosis was missed.

To put it bluntly, the screening itself is just a preliminary screening process, a bit like the security check we go through at the train station. If the security check does not detect contraband (negative), it most likely means that you did not bring it with you. However, it may also be that the contraband is hidden too concealed and the security inspection machine happened to scan the blind spot and failed to detect it. If you know that you have been exposed to high risk, or have symptoms corresponding to the screened diseases, you cannot take any chances even if you pass the security check.

If you do not feel any discomfort and have no history of high-risk exposure to the corresponding disease, you can basically rest assured after getting a negative result and conduct regular screenings according to the frequency of routine physical examinations; but if you have recently had clear high-risk contacts, or have symptoms that are highly related to the screened disease such as repeated coughing, abnormal bleeding, and long-term pain, don’t be careless even if you get a negative result.