Most injuries and aches don’t need an X-ray right away. For the majority of common complaints, like a tweaked ankle or a sore back, doctors use specific physical signs to decide whether imaging will actually change your treatment. Understanding those signs helps you know when to push for an X-ray and when rest and time are the better first step.
Ankle and Foot Injuries
A swollen, painful ankle after a misstep feels serious, but most ankle injuries are sprains that don’t involve a broken bone. Emergency physicians use a well-validated set of criteria called the Ottawa ankle rules to decide who actually needs an X-ray. You likely need one if you have pain near the bony bumps on either side of your ankle and at least one of the following: tenderness when pressing directly on those bones, tenderness along the back edge of the lower leg bones, or an inability to put weight on the foot for four steps both right after the injury and when you’re being examined.
For the midfoot (the area between your toes and ankle), the same logic applies. An X-ray is warranted if you have midfoot pain plus tenderness on specific bones in that zone or you can’t bear weight. If none of these criteria are met, the chance of a fracture is extremely low, and skipping the X-ray saves you time, cost, and a small dose of radiation.
Knee Injuries
Similar decision rules exist for the knee. A knee X-ray is recommended if you meet at least one of five criteria: you’re 55 or older, you can’t bear weight for four steps right after the injury and again at the clinic, you have tenderness only over the kneecap, you have tenderness at the head of the smaller bone on the outside of your lower leg (the fibula), or you can’t bend your knee to a 90-degree angle. If none of those apply, your injury is very unlikely to involve a fracture, and your doctor will typically recommend ice, compression, and follow-up instead.
Lower Back Pain
Back pain is one of the most common reasons people want an X-ray, and it’s also one of the situations where imaging is least likely to help early on. Acute low back pain lasting less than six weeks is considered self-limiting in most cases, and guidelines from the American College of Radiology recommend against routine imaging during that window unless red flags are present.
Red flags that do justify early imaging include:
- Signs of possible cancer: a history of malignancy, unexplained weight loss, pain that doesn’t improve with rest, fatigue, fever, or reduced appetite
- Signs of infection: intravenous drug use, recent urinary infection, immunosuppression, or prolonged steroid use
- Signs of fracture: significant trauma, or even a minor fall or heavy lift in someone who is elderly or has osteoporosis
- Signs of nerve compression: sudden loss of bladder or bowel control, numbness in the groin area, or progressive weakness in the legs
If you don’t have any of those warning signs, the standard recommendation is four to six weeks of conservative care (movement, over-the-counter pain relief, physical therapy) before considering imaging. Plain X-rays of the spine are generally only useful when fracture is the specific concern. For suspected disc problems or nerve issues, an MRI is far more informative than an X-ray anyway.
Chest and Lung Concerns
A chest X-ray is one of the most commonly ordered imaging studies, and it’s most useful when there’s a specific clinical suspicion to confirm or rule out. A persistent cough is the single most common reason doctors order one, accounting for about half of chest X-ray referrals in primary care. When pneumonia is suspected, a chest X-ray changes the treatment plan roughly 68% of the time, making it a high-value test in that scenario.
Your doctor is most likely to recommend a chest X-ray if you have a cough lasting several weeks, a cough with fever, shortness of breath that’s new or worsening, or abnormal lung sounds during a physical exam. For a simple cold or brief respiratory infection, imaging rarely adds useful information.
Dental X-Rays
The frequency of dental X-rays depends on your cavity risk. If you have active decay or a high risk for it, guidelines developed by the American Dental Association and the FDA recommend bitewing X-rays (the small images that show your back teeth) every 6 to 18 months. If you have no history of cavities and low risk, that interval stretches to every 18 to 36 months for adults and adolescents, and every 12 to 24 months for children with baby teeth.
A full-mouth series is typically reserved for new patients who show signs of widespread dental disease or who have had extensive past dental work. Your dentist shouldn’t be taking a full set of X-rays at every routine visit. If you’re cavity-free and your gums are healthy, asking whether you can extend the interval between imaging is reasonable.
Children and X-Rays
Children are more sensitive to radiation than adults because their cells are dividing more rapidly and they have more years ahead in which any damage could potentially matter. The FDA recommends that pediatric X-rays be performed only when they’re necessary to answer a specific clinical question or guide treatment, and that the lowest effective radiation dose be used every time. The guiding principle, supported by the Image Gently Alliance, is that doses should be adjusted based on the child’s size and age rather than using adult settings.
In practice, this means the same injury criteria that apply to adults (like the Ottawa rules for ankles and knees) apply to children too. A swollen wrist after a fall in a child who can still move it and has no point tenderness over the bone may not need immediate imaging. But children’s growth plates are vulnerable, so if there’s localized bone tenderness or significant loss of motion, X-rays are appropriate and the small radiation exposure is well worth it.
X-Rays During Pregnancy
X-rays of the arms, legs, chest, or head deliver almost no radiation to the uterus and are generally considered safe during pregnancy. The concern is with imaging that directly exposes the abdomen or pelvis. Even then, the risk is lower than most people assume. According to the American College of Radiology, radiation doses under 100 milligray cause no identifiable developmental effects, and that threshold is well above what a single diagnostic X-ray delivers. A standard chest X-ray, for example, exposes you to about 0.02 millisieverts, which is thousands of times below the concern threshold.
Higher-dose procedures like CT scans of the pelvis are managed more carefully, with a goal of keeping the dose to the fetus below 50 milligray. For procedures expected to exceed that level, a pregnancy test within 72 hours beforehand is standard practice. But a necessary X-ray should not be delayed or refused simply because of pregnancy if the clinical need is real.
How Much Radiation Are You Getting?
The natural background radiation you absorb just from living on Earth, breathing radon in your home, and eating food averages about 3.0 millisieverts per year. A single chest X-ray adds 0.02 millisieverts, roughly equivalent to two and a half days of that natural exposure. A dental X-ray (four bitewing images) adds just 0.004 millisieverts. An X-ray of a limb or joint delivers about 0.06 millisieverts. These are small numbers. The concern with radiation is cumulative and dose-dependent, so individual diagnostic X-rays pose very little risk when they’re clinically justified.
What to Expect at Your Appointment
Metal, thick fabric, and certain fasteners can block or scatter X-ray beams and create shadows on the image. What you need to remove depends on the body part being imaged. For a chest X-ray, you’ll remove necklaces and bras and change into a gown. For a knee X-ray, wear loose pants that can roll above the knee. For hand or wrist imaging, take off rings, watches, and bracelets. Cervical spine X-rays require removing earrings, hair clips, and necklaces. A simple rule: wear a plain T-shirt and avoid metal accessories if you know what’s being imaged.
The X-ray itself takes only a few minutes. A radiologic technologist positions you and captures the images, but they don’t interpret them. A radiologist reviews the images afterward and sends a report to the doctor who ordered the test. On weekdays, that radiologist report is typically available within a few hours. Studies done on weekends may not be read until the following Monday, with a median turnaround of about two and a half days. Your own doctor then reviews the report and contacts you, which can add additional time. If you’re in an emergency department, results usually come back much faster because the workflow is designed for urgent reads.