Co-Diagnostics (NASDAQ:CODX) might be the strongest growth stock in the market right now, with third-quarter revenue up about 50,000%. This is a bit of a misleading statistic, as the company had only $41,000 in revenue at this time last year. Nonetheless, to drive sales from such a tiny base to $21 million is really impressive. And while companies in hypergrowth mode are rarely profitable, Co-Diagnostics is an exception. Indeed, the company reports net margins of 63% so far in 2020.

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So here's a company with amazing 50,000% revenue growth, and profit margins superior to Visa. It's not surprising that early investors have enjoyed a beautiful 11-bagger so far in 2020. In fact, we might ask why the stock hasn't gone a lot higher.

Co-Diagnostics has a price-to-sales ratio under 6, and a forward P/E of 6 as well. That's incredibly cheap for a company with skyrocketing sales growth. Why is the stock market unwilling to give this diagnostic company a higher multiple?

Co-Diagnostics has diagnostics for multiple diseases, including one for tuberculosis bacteria, and another test for the Zika virus. But of course in 2020, what's driving all the revenue growth is COVID-19 testing.

The stock market appears skeptical about how much of the company's revenue growth is sustainable. What happens to the COVID-19 testing market if we're all vaccinated against this virus?

Key questions for investors are whether COVID-19 testing will start to decline, and whether Co-Diagnostics can successfully market other products. For now, I'm staying on the sidelines. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.