Mammography is the best tool for doctors to find breast cancer. A mammogram captures crisp, digital X-ray images of the breasts that can help radiologists locate anything from benign cysts to cancer.

There are two types of mammogram appointments: screening and diagnostic. They are both used to detect cancer, but there are distinctions. We break down the differences between a screening mammogram versus a diagnostic mammogram — and when you should act to potentially catch breast cancer early.

What is a screening mammogram?

Screening mammograms are routine X-rays used to spot signs of breast cancer early.

"A screening mammogram is for an asymptomatic patient — someone who doesn't have any problems with their breasts, who is just coming in for annual screening," says Dr. Kelli Ha, a breast radiologist with Houston Methodist. "We do them approximately once every 12 months."

The American College of Radiology and U.S. Preventive Services Task Force recommend that women start screening mammograms at age 40 unless there's a first-degree family history — a mom or sister diagnosed with premenopausal breast cancer.

"If your mom or sister was diagnosed in their 40s or even in their 30s, we start mammograms 10 years before these family members were diagnosed," Dr. Ha says.

For any women having breast cancer symptoms such as nipple discharge, breast lump, focal breast pain (pain in one spot of the breast), or any changes to the size, shape or skin of the breast before age 30, Dr. Ha says that radiologists will start with a breast ultrasound first since younger patients are more sensitive to radiation.

(Related: 5 Things to Know About the Recent Updates to Mammogram Guidelines)

What is a diagnostic mammogram?

"If you're over the age of 30, and you have a breast lump, focal pain, nipple discharge, or you have had an abnormal mammogram, these issues get addressed with a diagnostic mammogram," Dr. Ha says.

Some patients will get called back to have a diagnostic mammogram after a screening mammogram. However, if you are over the age of 40 and have symptoms, you should contact your primary-care doctor before scheduling a mammogram. They can order a diagnostic mammogram first — which can help you get answers sooner.

"We try to tell patients not to schedule a screening mammogram unless you are truly asymptomatic," Dr. Ha says. "If you have a lump or nipple discharge, we want you to have a diagnostic mammogram, so we can evaluate the area of concern more thoroughly.

"We have a marker that we put on the breast, and this calls attention to the area where the patient is feeling something," she adds. "We still look at both sides, but the marker is put on the breast to help hone in on what the problem is that day."

Differences between screening versus diagnostic mammograms

"They're similar but different," Dr. Ha says. "We start with the same four views — squishing the breast from top to bottom and from side to side on both sides. However, the difference is that we can take additional views if needed with the diagnostic mammogram as the radiologist is looking at the mammogram real-time."

Screening mammograms can take anywhere from 10 to 15 minutes to complete the four views. In contrast, diagnostic mammograms can take longer since technicians may take additional spot compression or magnification views for any areas of concern. Patients then get a diagnostic ultrasound which can further evaluate the problem during a diagnostic appointment as well.

Diagnostic mammograms will be read and interpreted the same day — results are typically available as the radiologist looks at the images while the patient is in the breast center. Screening mammogram results take longer to get back, though Dr. Ha emphasizes that's because preference is given to reading diagnostic mammograms first.

"The idea is that screening mammograms are read in between diagnostic mammograms," Dr. Ha said. "With diagnostic mammograms, we're trying to solve a problem and let the patient know results before they leave the breast center."

The scoring system for screening and diagnostic mammograms is the same

In both cases, radiologists use the Breast Imaging Reporting and Data System (BI-RADS) system to score the exams.

"They are both scored the same — they go from a zero to a five," Dr. Ha says. "If we see something on a screening mammogram, and we want patients to come in for additional images, they are given a BI-RADS zero."

This means that they will come in for a diagnostic mammogram to evaluate the area of concern. For "normal" mammograms that don't show any abnormal or questionable findings, a BI-RADS 1 or BI-RADS 2 is given.

"Essentially, a zero is indeterminate; the patient is brought back for additional imaging," says Dr. Ha. "A one or two means it is normal, with no additional work-up needed. Three means we would like to follow something — it is literally called a 'probably benign' category. It means that the finding has a 98% likelihood of being benign."

For mammograms scored with a BI-RADS 3, Dr. Ha says that doctors will ask for a six-month follow-up appointment. Probably benign findings are usually followed for two years.

"BI-RADS 4 means the findings are indeterminate and that a biopsy is recommended. BI-RADS 5 means it is almost definitely cancer and needs a biopsy," Dr. Ha says.

Got a call to schedule a diagnostic mammogram? Don't panic

If you have a screening mammogram and get called back, it can be easy to start worrying. While easier said than done, try not to let anxiety take over. As Dr. Ha says, just because you get called back doesn't mean you have breast cancer.

"I think it is scary regardless, especially if you're an anxious person," Dr. Ha says. "But [a callback] means we want to look at something more closely. There are a few things that can show up on a mammogram that are benign and not cancerous, but they still need to be evaluated. Unfortunately, a percentage of those patients will have cancer; but the majority of patients that are called back actually do not have cancer. A diagnostic mammogram and ultrasound can help clarify which is which."