There's no foolproof way to know the future for Martek Biosciences (Nasdaq: MATK) or any other company. However, certain clues may help you see potential stumbles before they happen -- and before your stock craters as a result. Rest assured: Even if you're not monitoring these metrics, short-sellers are.

A cloudy crystal ball
I often use accounts receivable (AR) and days sales outstanding (DSO) to judge a company's current health and future prospects. It's an important step in separating the pretenders from the market's best stocks. Alone, AR -- the amount of money owed the company -- and DSO -- days worth of sales owed to the company -- don't tell you much. However, by considering the trends in AR and DSO, you can sometimes get a window onto the future.

Sometimes, problems with AR or DSO simply indicate a change in the business (like an acquisition), or lax collections. However, AR that grows more quickly than revenue, or ballooning DSO, can also suggest a desperate company that's trying to boost sales by giving its customers overly generous payment terms. Alternately, it can indicate that the company sprinted to book a load of sales at the end of the quarter, like used-car dealers on the 29th of the month. (Sometimes, companies do both.)

Why might an upstanding firm like Martek Biosciences do this? For the same reason any other company might: to make the numbers. Investors don't like revenue shortfalls, and employees don't like reporting them to their superiors.

Is Martek Biosciences sending any potential warning signs? Take a look at the chart below, which plots revenue growth against AR growth, and DSO:

Matk


Source: Capital IQ, a division of Standard & Poor's. Data is current as of last fully reported fiscal quarter. FQ = fiscal quarter.

The standard way to calculate DSO uses average accounts receivable. I prefer to look at end-of-quarter (EOQ) receivables, but I've plotted both above.

Watching the trends
When that red line (AR growth) crosses above the green line (revenue growth), I know I need to consult the filings. Similarly, a spike in the blue bars (DSO) indicates a trend worth worrying about. As another reality check, it's reasonable to consider what a normal DSO figure might look like in this space.

Company

LFQ Revenue

DSO

 Martek Biosciences $119 53
 Procter & Gamble (NYSE: PG) $20,122 26
 Archer-Daniels-Midland (NYSE: ADM) $16,799 39
 Monsanto (NYSE: MON) $1,953 114


Source: Capital IQ, a division of Standard & Poor's. DSO calculated from average AR. Data is current as of last fully reported fiscal quarter. LFQ = last fiscal quarter. Dollar figures in millions.

Differences in business models can generate variations in DSO, so don't consider this the final word -- just a way to add some context to the numbers. But let's get back to our original question: Will Martek Biosciences miss its numbers in the next quarter or two?

The numbers don't paint a clear picture. For the last fully reported fiscal quarter, Martek Biosciences' year-over-year revenue grew 36%, and its AR grew 57%. That's a yellow flag. End-of-quarter DSO increased 15.4% over the prior-year quarter, but it was up just 3% versus the prior quarter. That still demands a good explanation. Still, I'm no fortuneteller, and these are just numbers. Investors putting their money on the line always need to dig into the filings for the root causes and draw their own conclusions.

What now?
I use this kind of analysis to figure out which investments I need to watch more closely as I hunt the market's best returns. However, some investors actively seek out companies on the wrong side of AR trends in order to sell them short, profiting when they eventually fall. Which way would you play this one? Let us know in the comments below, or keep up with the stocks mentioned in this article by tracking them in our free watchlist service, My Watchlist.

The Fool owns shares of and has written covered calls on Procter & Gamble, which is a Motley Fool Income Investor choice. Motley Fool Options has recommended a synthetic long position on Monsanto. Try any of our Foolish newsletter services free for 30 days.

Seth Jayson had no position in any company mentioned here at the time of publication. You can view his stock holdings here. He is co-advisor of Motley Fool Hidden Gems, which provides new small-cap ideas every month, backed by a real-money portfolio. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.