While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a closer look at particularly stock-shaking analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Hologic (NASDAQ:HOLX) sank 3% this morning after BTIG downgraded the medical diagnostics company from buy to neutral.

So what: Along with the downgrade, analyst Sean Lavin reiterated his price target of $26, almost exactly where the stock closed this past Thursday. So while momentum traders might be attracted to Hologic's price strength in recent months, Lavin's call could reflect a sense on Wall Street that the risks surrounding its growth trajectory are being largely overlooked.

Now what: According to BTIG, Hologic's risk/reward trade-off isn't too attractive at this point. "Several months ago, HOLX traded ~3 points below the group on an earnings basis. Now, the company trades with or above peers and has reached our $26 PT," said Lavin. "HOLX trades at ~17.6x NTM EPS vs. peers at 18.2x and due to debt has an EV/Sales of 4.3x vs. an average of 2.9x. While we do not feel shares are overvalued, we do not see valuation metrics that make sense here to offer the 15% upside required for a BUY rating." When you couple that seemingly stretched valuation with Hologic's still-hefty debt load, it's tough to disagree with BTIG's cautiousness.