We’ve known for decades that a small fraction of Americans incurs the bulk of health care costs. A report released last month by the National Institute for Health Care Management (NIHCM) analyzes 2009 data to shed light on the patients we should worry about most. Their findings take on special relevance in the wake of Massachusetts lawmakers passing an ambitious health care cost control bill.

As health care spending increases across the board, the cost distribution is becoming a bit less skewed – probably because more Americans are developing risk factors like obesity that lead to chronic and costly conditions like diabetes and heart disease, according to the NIHCM report. Still, in 2009, 1% of the U.S. civilian patient population ran up more than 20% of the nation’s health care bill at a cost of $90,000 per patient while 5% of the population accounted for nearly 50% of spending at a cost of $41,000. In contrast, the lowest spending 50% of the population spent an average of $236 that year, they found.

Here’s what they learned about the highest cost patients: Not surprisingly, they were more likely to be older and have more chronic conditions and functional limitations than the rest of the population. Their most common ailments were high blood pressure, high cholesterol, and diabetes. In the 65+ set, joint problems were among the top four conditions, whereas in the non-elderly, mood disorders made the cut.

The authors also found that the highest cost patients were a moving target. Of the top decile (highest 10%) of spenders in 2008, only 45% remained in that group the next year; 25% of patients in the original group lowered their spending to count among the bottom 75% of spenders the next year. The report doesn’t mention the fate of the other 30% of patients who were in the top decile in 2008, but I’d expect (and other analysis suggests) that a good portion of them (particularly the elderly) passed away.

So high cost patients are not all the same. The way I see it, we can think about these patients in three broad categories that have implications for their care:

The patients who remained top spenders from year to year are the ones with chronic conditions and disabilities. Say, a 60-something woman with asthma and congestive heart failure who lands in the hospital multiple times a year with exacerbations of the same. She and others like her have been poorly served by the traditional health care system. These are the patients profiled in Atul Gawande’s The Hot Spotters, those who would do much better (and require fewer hospitalizations) with the help of visiting nurses to sort their medications, case managers to navigate them through the health care system, and social workers to address the struggles with food and housing that are so closely intertwined with health.

The patients that bounced back from the highest spending category (who were younger, by the authors’ calculation) may have been completely healthy before they were hit by a catastrophic event. Imagine the 30-something guy who has a skiing accident that requires multiple orthopedic surgeries. The next year he’s back to life as usual. These patients may benefit (and their costs might decrease) from efforts to make hospital processes more efficient and reduce surgical complications, for example.

Patients who were top-spenders at the end of their lives deserve special consideration, both from a cost and a humanistic perspective. This is the 90-something man who comes in for an acute worsening of his leukemia and gets a barrage of chemotherapy and intensive-level care in the moments before his death. Which interventions truly improve quality of life for these patients? Are doctors doing them a service by pulling out all the stops? Such discussions enter politically and ethically challenging territory, but are all the more important to broach with patients and at a systems level.

The more we understand about the patients we care for and target our interventions to meet their needs, the better our chances of providing quality health care that won’t cripple our economy.

Ishani Ganguli is a journalist and an internal medicine-primary care resident who blogs at The Boston Globe’s Short White Coat, where this article originally appeared.