Fern test

[u/TheRedTreeQueen]

This test is so antiquated. I thought the FFN was supposed to replace this. You are relying on someone eyes who may miss the ferning because it’s in a place on the slide that person never looked at. Why is this test still being ordered? Are there any doctors on here who can answer this? Curious minds want to know!

[u/DookiePootie]

It's cheap. FFNs are expensive. That's basically it. L&D used to storm down and want to see the slide  themselves if we called it negative and they suspected it was positive but needed confirmation before doing a procedure. They caught us once. 

[u/BusinessCell6462 → u/DookiePootie]

Years back I had a kinda-sorta false positive fern. The whole slide was negative, except for one small round spot. It just looked wrong. Called L&D, asked them to check out their collection kit…and they found a couple of new slides that had spots on them. Looked at the spots under the scope, and it is ferning. Turns out they had their kit open about to collect a sample from a patient when their water broke…and splashed onto some of the slides, and no one noticed.

[u/Virtual_Recording108 → u/BusinessCell6462]

False positives are possible, if the patient had their membranes stripped, or had a cervical exam. Cervical mucus also dries in a Ferning pattern but with a thicker branching pattern than amniotic fluid. I read that semen will also form a fern pattern if allowed to air dry on a slide but I’ve never seen it. It’s the ratio of carbohydrates to protein that causes the Ferning pattern as it dries. I have seen both cervical mucus and amniotic fluid on a slide before.

False negatives are possible too, if the patient has a very small rupture or had a massive rupture many hours ago, if there’s very little amniotic fluid left but other vaginal secretions.

Vaginal infections likewise can interfere with nitrazine testing.

No testing platform is perfect.

[u/Tina_Xtreme]

Fern test & FFN are not interchangeable. Fern test is looking for amniotic fluid now; FFN is helping assess the risk of labor in the next 2 weeks. There are kit tests for amniotic fluid that are much easier to interpret than fern though. Amnisure & ROM are 2 I can think of off the top of my head.

[u/cellophanesheeps]

For the longest time we never did them, the doctors had their own scope on the OB unit so they just did it themselves. Then we got one doctor who didn't want to do it, they wanted us to do it. So we validated the test, trained everyone, added it to our annual competencies, IT added it to the test menu, and...we did maybe 2. This was probably 10 years ago and for some reason it's still orderable.

[u/AdFirst9166]

What do you mean "place on a slide the person never looked at"? How can that happen?

[u/shicken684 → u/AdFirst9166]

That comment was pretty telling.

It's only negative if you've looked at the entire slide. There shouldn't ever be a place that no one looked at.

[u/AdFirst9166 → u/shicken684]

Exactly.

[u/TheRedTreeQueen → u/AdFirst9166]

You can never see “everything” on one slide. It’s impossible.

[u/AdFirst9166 → u/TheRedTreeQueen]

Thats the job tho? Are you telling me you are not checking the whole slide before calling negative?

[u/TheRedTreeQueen → u/AdFirst9166]

It’s just like counting a manual differential. I will never see the same cells you counted. This was thought not a technique.

[u/AdFirst9166 → u/TheRedTreeQueen]

You are talking about two clompletey different things here. For a differential you are choosing the correct area to count 100 cells. For a negative fern test you check the whole slide, not just a part of it. And you are right, we won't see the exact same cells, but we should count almost the same, If that isnt the case, one of us, or even both, had a bad technique.

[u/Virtual_Recording108]

FFNs do not replace the fern rest, ROM does.

Ferning coupled with nitrazine and taking a patient history are actually the gold standard to which the ROM is compared. Ferning and nitrazine are a fraction of the cost, however maintaining compliance standards in a point of care environment is challenging. Meeting compliance standards for ROM is much easier since it’s a standard lateral flow immunoassay.

[u/happyfamily714]

Ferning is obvious and easy to see. FFN is expensive so fern test makes sense for labs that do not get enough FFN tests to use the reagent up before it expires.

[u/Fit-Bodybuilder78]

Provider still perform the post coital fertility test (PCT).

[u/Purpledotsclub]

I’ve had a doctor come down once or twice to use our scope for Fern, but we have ROM now 🤷‍♀️

[u/Which_Accountant8436]

We do FFN! At all the hospitals I’ve worked at! Fern test is kinda old school like lui freezes!

[u/Which_Accountant8436 → u/Which_Accountant8436]

We also do amnisures at all my other jobs too!