视频：为什么试剂盒有时候不管用？

researchers around the world are hustling to create this test kit

a rapidly spreading corona virus has put the test kit at the center of how patients are diagnosed 

so they can get treatment quickly

but there is one issue with these nose and throat swabbing tests

the results aren't always accurate

at the center of the epidemic in Wuhan

some people tested negative

only later to find out that they actually have the disease

in the US, the CDC sent out test kits to public-health la bs that gave inconclusive results in verification process  

the unreliability of these tests even forced Chinese health officials to expand how they classify patients

which results in a surge of more than 14,000 cased in one day 

they are now including results from test kits and other diagnostic methods like chest scans

so how do these test kits exactly work and why are there so many problems

this government lab in Singapore has produced test kits for the country's public hospitals

it's also shipped over 10,000 tests to China

Dr. Sydney Yi leads a team that developed them

she says most doctors use a type of lab test called RTPCR

which can be used to test small amounts of pathogens 

including viruses like HIV

so this is the gold standard that's been used

what it does is that it actually directly detects the presence of the pathogen

it is pretty easy to use

a doctor collects samples from a patient by swabbing the nose or throat for mucus

those swabs are then sent to a lab for a test that detects the genetic material of a pathogen 

the sample is first mixed with reagents in a tube

then put into a machine that duplicates the genetic material

though the virus exists, these copies will amplify its presence 

confirming that a patient has tested positive for the corona virus

Dr. Yi says the first place for error could be at the swabbing stage

most of the time, the sampling for Covid-19 comes from throat swab

Covid-19 is actually a lung-infection disease

so, the throat swab really depends on how much of the pathogen you are able to capture

another place for error is the time it takes for the sample to reach the lab

pathogen on the swab is not going to last for many many hours

so, the transportation, the logistics are so important

transportation is a huge hurdle in Wuhan

where the city has been on lock-down since mid January

when the sample gets to the lab

what is the infrastructure of the lab? 

that is -able to deal with running tests

as well as the expertise and experience of the lab technicians that are running these tests

Dr. Yi says the most critical moment for human error

is when doctors decide to use a test kit

for instance, many people have been showing mild symptoms

but that doesn't mean they don't have the pathogen

it's very hard to make the direct correlation 

between what our test kits can be used on which stage of the disease's progression

with respect to how much the pathogen is present in the patients

just how accurately these test kits are being used is on trial in Wuhan

here, hospitals have been overstretched with limited resources

there are not enough staff to swab the patients 

and labs are inundated with a backlog of samples waiting to be tested

there are many many different steps and different processes involved

in just running a test

it's not just with respect to the test kit itself