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 upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Thermo Fisher Scientific (NYSE:TMO) gained about 1.5% in pre-market trading, and the stock remains in positive territory after Goldman Sachs upgraded the health care instrument company from neutral to buy.

So what: Along with the upgrade, analyst Isaac Ro boosted his price target to $153 (from $114), representing about 26% worth of upside to yesterday's close. While contrarians might be turned off by Thermo's share-price strength over the past year, Ro believes there's plenty of room to run given the long-term growth tailwinds continuing to work in the company's favor.

Now what: Goldman sees significant positives ahead for Thermo:

"Catalyst (1) Better than expected organic growth: Outsized scale and pricing power should help drive long-term organic growth of 5%, 100bps ahead of consensus. ... (2) Better than expected EPS growth: Our bottom-up analysis leads us to model cost synergies that are 40% above guidance. ... (3) End markets improving as TMO emerges better positioned: Government funding is improving as US austerity fades, EU has stabilized, and Japan Stimulus buttresses demand," noted Ro.

When you couple those positive trends with Thermo's still-reasonable forward P/E of 15, it's tough to disagree with Goldman's bullishness. 

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Brian Pacampara has no position in any stocks mentioned. The Motley Fool recommends Thermo Fisher Scientific. Try any of our Foolish newsletter services free for 30 days. 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.