The past three years have been a roller coaster for Abbott Laboratories (ABT -0.33%). The healthcare giant dealt with a slowdown in its medical device business caused by the pandemic, fluctuating sales of its coronavirus diagnostic tests, and a recall of some of its baby formula products. Abbott's financial results haven't been consistent, partly explaining why it has lagged the market this year.

However, there remain excellent reasons to buy shares of the company. Let's consider why Abbott Labs is an outstanding "forever" stock. 

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The core business is performing well

Abbott's top-line growth rates have been negative all year long. In the third quarter, net sales declined 2.6% year over year to $10.1 billion. However, these are apples-to-oranges comparisons. COVID-19 cases -- and the need for diagnostic tests -- fell in the third quarter compared to last year's parallel period. It's more important to look at Abbott's performance minus its coronavirus diagnostic testing unit.

On that front, the company is doing well. In the third quarter, its sales grew by 13.8% organically, not including sales of COVID-19 testing kits. Further, out of its four major reporting segments, three of them saw sales increases: nutrition, established pharmaceuticals, and medical devices. Predictably, the company's diagnostics segment was the only exception to the rule.

Medical devices, Abbott's largest segment by revenue, saw the most significant sales growth at 16.6% year over year. The company's earnings per share of $0.82 was just barely better than the $0.81 reported in the year-ago period. Still, Abbott's overall results were solid, especially if we focus on the most important aspects of its business. 

Abbott's key growth driver still looks exciting 

Abbott's portfolio of medical devices is vast and spans multiple therapeutic areas, from heart failure and rhythm management to electrophysiology. However, the company's most important product line comes from its diabetes care unit. Abbott's FreeStyle Libre franchise has been its most important for some time now. The FreeStyle Libre is a series of continuous glucose monitoring devices that allow people with diabetes to track their blood sugar levels in real-time.

FreeStyle Libre sales in the third quarter jumped by 28.5% organically to $1.4 billion -- representing almost 14% of the company's net sales. There have been concerns that highly popular weight-loss drugs such as Wegovy -- developed by Novo Nordisk -- could decrease the need for CGM devices, thereby harming Abbott's business. It doesn't seem like that happened during the third quarter.

Management has downplayed those fears, highlighting that the percentage of patients taking weight-loss medicines represent a tiny percentage of the vast global diabetes market. Further, Abbott is preparing to launch a new franchise of wearables called Lingo. While not specifically designed for the management of diabetes, these new devices build on the technology that powers Abbott's FreeStyle Libre.

Lingo will help people make more informed decisions about their health by allowing them to track such metrics as glucose, ketones, and lactate. The healthcare giant has estimated that this franchise could be as big as the FreeStyle Libre line of products. Abbott Laboratories is initially launching Lingo in the U.K. and plans to request clearance in the U.S. by year-end.

A steady and reliable dividend-payer

Be it with the FreeStyle Libre franchise, the newer Lingo, or some other product lines -- of which there are many -- Abbott Laboratories has proven time and time again that it is an innovator, a key reason it can continue to deliver excellent financial results for a while.

Here's another indicator of the company's ability to deliver over the long run. Abbott Laboratories is a Dividend King currently on its 51st consecutive year of dividend increases. The company's dividend yield of 2.20% is higher than the S&P 500's average of 1.62%, while its cash payout ratio of 63% is reasonable.

Abbott Laboratories' dividend is just one more reason the company's shares are a buy today, especially as its stock has significantly lagged the market this year. And given the strength of its core operations, excellent track record of earnings growth, and ability to develop innovative devices, the stock still looks like an excellent buy for long-term investors.