system
Given the following post, respond as if you're commenting on Reddit:
human
Why has early detection of diseases via dogs not found widespread use in medicine?

I have heard how dogs can detect diseases such as cancer or now covid with a surprisingly high accuracy. However I have not seen widespread use of dogs in such a manner.
gpt
Consistency issues.

In some cases, researchers don't know exactly what chemical compounds the dogs are detecting.  That remains a hurdle for training better sniffer dogs but also for designing better detection devices.

Competition with AI detection devices.  Robots are pretty good at this stuff too, plus they work 24/7 and can usually do high-throughput.

Difficult to move dogs around - easy to move tiny vials of samples.  Standard clinical or pre-clinical testing is very robust and efficient. 
 Compare to that it's more difficult to collect/store/analyze samples of breath, sweat, smelly socks or whatever the dogs are smelling.

Trained service dogs cost anywhere from $20k-$50k each.  Sometimes higher still.  For them to work, a patient needs to visit a clinic that owns a dog or present a dog with a sample.  There will be a limit to number of patients per day, per dog.  That means cost per test gets very high.

Reject dogs and test-on-demand.  Ethical questions are breeding dogs do tasks like this.  Usually a lot of dogs fail training, and then what?  OR how long per day can the dog do tests before it gets fatigued.  False positives and false negatives.

Skepticism remains high in medical community.  Historically, everything is moving to robots and controlled lab testing.  Moving back to animals seems like an odd quirk that will quickly be replaced by an AI sensor.