Amniotic Fluid Question...

Idk if anyone can answer this, but I've noticed a trend amongst other women:

What is the point of doing a swab test of fluids to check if amniotic fluid is leaking when the majority of the time the test comes back negative (or inconclusive), when in fact it IS amniotic fluid? If that makes sense...

So many women say this and it happened to me in the ER last pregnancy when I lost my son at 17+3 weeks. They said I peed myself (which I didn't.) And when I went to ultrasound, they confirmed that I had oligohydramnios (no fluid left.)

Shouldn't there be a better test? What's the point in even checking if they have to double check via ultrasound to confirm?

Just curious 😊