E arly detection is critical to good health. Many diseases are curable in their early stages. And proper diet, not smoking, exercise and other healthful habits are important in preventing disease.

First step: Find out if a disease runs in your family, especially in parents, grandparents and siblings. If any of these relatives have suffered from diabetes, heart disease, stroke, breast cancer, colon cancer or other disorders, consult your doctor to see if you are a candidate for special testing or precautions.

Even people from the healthiest families require routine medical tests. These first, routine steps are the ones that could end up saving your life:

DO-IT-YOURSELF TESTS

Women: Examine your breasts once a month. Use the pads, not the tips, of your fingers to feel for lumps or other abnormalities.

Men: Examine your testicles once a month, checking for lumps or enlargements. Testicular cancer is the most common form of cancer in young adult men.

Tests for everyone to do regularly:

Inspect your skin. Look over your moles for changes in size, color or shape. Watch for new moles, especially those larger than the diameter of a pencil eraser. Enlarging moles or those with an irregular border or uneven coloring should be brought to your doctor’s attention immediately.

Thyroid self-exam. Look in the mirror, focusing on the lower part of your neck below your voice box. If the area appears enlarged or irregular, or if there’s a visible lump when you swallow, see a doctor for further examination.

ROUTINE SCREENING TESTS

Every adult should have a physical in a doctor’s office once every one to two years before age 40, and once a year after that. Here’s what needs to be checked:

Blood pressure. An optimal reading is 120/80, but a blood-pressure level less than 140/90 is within normal range.

Cholesterol: Should be monitored at least once every five years during adulthood, more frequently if it’s elevated. If your reading is over 200, then you should also take what’s called a fasting total cholesterol test (taken after not eating for 12 hours), which includes LDL ("bad" cholesterol) and HDL ("good" cholesterol) and triglycerides (a type of fat in your blood). Recommended levels:

LDL should be under 130.

HDL over 45.

Triglycerides should generally be less than 150.

Blood glucose: Diabetes is the sixth-most-deadly disease in America. Starting at age 45, a fasting blood sugar test should be repeated every three years, more often if a person is obese or has a family history of diabetes.

Rectal exam: Recommended for people after they turn 40. The doctor will most likely also give you a fecal occult blood test. The presence of blood in your stool can mean a number of things, including colon cancer, so it needs to be investigated further.

Sigmoidoscopy or colonoscopy: Many health-care professionals now recommend one or the other, usually with stool card testing, starting at age 50, or age 40 or even earlier if there is a family history of colon cancer.

During a sigmoidoscopy the doctor examines the lower portion of your colon, where polyps or tumors are most likely to occur.

A colonoscopy covers the entire length of the colon and is usually recommended for people at higher-than-average risk for colon cancer.

Skin screening: Consists of a visual examination of your skin, in a search for abnormal lesions that suggest melanoma or other skin cancer. See a dermatologist once a year if you have a history of skin cancer, dysplastic skin lesions (a precursor to melanoma), or a family history of melanoma.

Thyroid blood test: A malfunctioning thyroid is relatively common and easily treated. Untreated, it can lead to serious complications including increased risk for heart disease. Some experts recommend testing every three to five years.

Eye exam: Every one to two years to screen for glaucoma and other eye disorders.

FOR WOMEN ONLY

Pap smear for cervical cancer: Should be done every year, starting at age 20, or even earlier if a woman is sexually active. Risk of cervical cancer is increased with exposure to certain viruses that can be sexually transmitted.

Clinician breast exam and mammogram: The clinician breast exam should be done at the time of the physical.

The mammogram X ray reveals abnormalities in the breasts, and is indicated every one to two years for women age 40 to 49, and annually for women over 50. Have a baseline test done between ages 35 and 40.

Bone-density scan: Women should have this done beginning at age 65, or earlier if there’s a family history or other risk factor for osteoporosis, or to help make a decision about hormone-replacement therapy.

FOR MEN ONLY

Digital prostate exam: While performing the rectal exam, your doctor will also feel for any enlargement of your prostate, which could signal cancer.

Examination of the testicles: The doctor will search for lumps or nodules, which could indicate testicular cancer.

Prostate-specific antigen (PSA) blood test: It identifies proteins that can signal the presence of prostate cancer. Some experts recommend this test every year, beginning at age 50, or earlier if there is any family history of the disease.