(Center for the Advancement of Health) -- A new study shows that the percentage of outpatient mastectomies increased dramatically between 1990 and 1996, particularly in certain states.

"While clinical factors remain important, the state in which a women undergoes a complete mastectomy and her primary payer greatly influence the choice of outpatient location for a complete mastectomy," says senior author Claudia Steiner, M.D., M.P.H. of the Agency of Healthcare Research and Quality in Rockville, Maryland.

Researchers reviewed hospital discharge records for all women who were treated with an excisional breast procedure for cancer in the states and years for which consistent inpatient and outpatient surgery data were available (between 1990 and 1996 in Colorado, Maryland, New Jersey and New York and between 1993 and 1996 in Connecticut).

Excisional procedures included lumpectomy, subtotal mastectomy and complete mastectomy. In addition to looking at geographic location, researchers evaluated the influence of severity of illness, insurance coverage, extent of procedure and hospital characteristics on the decision to treat the surgeries as outpatient or inpatient procedures.

The study appears in the October issue of Health Services Research.

Most lumpectomies were performed as outpatient surgeries throughout the study period. By 1996, 78 percent to 88 percent of women undergoing lumpectomy were sent home without an overnight stay.

The incidence of subtotal mastectomies performed on an outpatient basis increased from a range of approximately 10 percent to 50 percent in 1990 to 43 percent to 72 percent in 1996, depending on the state where the surgery was performed. While the rate increased in all locations, it was much more dramatic in some states. The percentage of outpatient subtotal mastectomies in Colorado, for example, increased from only 10 percent in 1990 to 67 percent in 1996.

The incidence of outpatient total mastectomy was barely above zero in any state in 1990. However, by 1996 the incidence had increased to 3 percent in New Jersey and 4 percent in New York, but was 8 percent in Connecticut, 12 percent in Maryland, and 22 percent in Colorado.

Insurance coverage also influenced whether a complete mastectomy was followed by a hospital stay. Among Medicaid patients, 97 percent were kept in the hospital after their surgery, while 94 percent of Medicare patients stayed in the hospital. By comparison, 89 percent of HMO patients were kept in the hospital. .

Women who were more seriously ill were more likely to remain hospitalized. The incidence of outpatient surgery was lower for patients who also had other illnesses, needed breast reconstruction, or whose cancer had spread.

Study results also show that women were less likely to have outpatient surgery if the procedure was performed at a publicly funded or teaching hospital.

"Although direct costs of outpatient surgery compare favorably, the indirect costs of additional outpatient visits, home health care, which may not be a covered benefit for many patients, and family caretakers providing additional support have not been fully studied," says Steiner.

"Decreases in the length of stay have rekindled concerns that the gains in health care savings may be at the expense of health care quality," says Steiner. "Quality must continue to be monitored."