I've used Trace Analytics (airchecklab.com) and Lawrence Factor (X-Zam Labs)
The Lawrence Factor kit to test for OCA $134.00 (single test). You pay for shipping back.
The Trace Analytics kit to test for OCA is $110.97 (single test). Prepaid shipping label is included.
They both give you discounts if you sign up for quarterly testing{/quote]
If testing to the OCA standard (which isn't really a recognized standard. It's just something the scuba industry made up) costs more then it's not worth the extra money. The method is the same for OCA, CGA Grade E, whatever.
I can't speak on the accuracy of either testing method but the Lawrence Factor kit is easier to use although neither are particularly difficult.
The accuracy for what our industry needs is adequate from both labs.
I test the right before my filter changes to in theory see the worst quality air I am producing. I've never not met OCA. From my understanding most compressors will produce this (at least for a short period of time) out of the box.
They will, for a long period of time. My compressors have filters that are rated for 50 hours. Just for fun I tested one of them every 10 hours (because I could) to see when the filters starting to go off. I got up to 120 hours before the moisture started to fail but I was still meeting OCA ( just like RJack said, test for moisture to see when your filters are going off because if the moisture is failing, your filters are failing)