If you have back pain, the odds are strongly in your favour. The large majority of low back pain is what clinicians call non-specific: painful, sometimes very limiting, but not caused by anything dangerous. Serious underlying causes such as fracture, infection, cancer or cauda equina syndrome account for a small percentage of the back pain seen in primary care.1
But "small" is not "zero," and the consequences of missing one of those cases can be severe. So every good assessment starts with a set of questions designed to pick up the warning signs. This article walks through those signs in plain language, explains why each one matters, and tells you what to do if you recognise one. It is written for patients, and it is not a substitute for being examined.
Why red flags exist
Red flags are symptoms or features in your history that raise the probability of a serious cause enough to justify closer investigation. No single flag is a diagnosis. Many are individually weak predictors, and most people with one red flag turn out to have nothing serious.2 What matters is the combination, the trajectory, and the judgment of the person examining you. The international framework published by Finucane and colleagues in 2020 is the clearest modern guide, and it emphasises exactly this: red flags are prompts for closer attention, not automatic alarms.3
The symptoms that mean go to the emergency department today
These are the cauda equina symptoms. The cauda equina is the bundle of nerve roots at the bottom of the spinal cord, and compression of it, usually from a large disc herniation, is a surgical emergency. Delay can mean permanent loss of bladder, bowel or sexual function.4
- New difficulty starting urination, a weak stream, or a feeling that you cannot fully empty your bladder
- Loss of bladder or bowel control, or not being able to feel when you need to go
- Numbness or altered sensation in the area that would touch a saddle: the inner thighs, genitals, and around the anus
- New sexual dysfunction, including loss of sensation
- Progressive weakness or numbness in both legs
If you have back pain and any of these symptoms are new, do not wait for a clinic appointment. Go to the emergency department. Many of these early signs are subtle, and people often feel awkward mentioning bladder or sexual changes. Please mention them anyway. Early cauda equina symptoms are the ones that are most treatable.
The symptoms that mean see a doctor soon
These do not usually need the emergency department, but they warrant a same-day or next-day medical assessment rather than a wait-and-see approach.
Possible fracture. Back pain after a significant fall or collision; a new, sudden onset in anyone over about 65 or 70; or pain after even minor strain in someone with osteoporosis or long-term steroid use. Vertebral compression fractures can happen with surprisingly little force when bone is weak.
Possible cancer. A history of cancer is the strongest single predictor here, particularly cancers known to spread to bone such as breast, prostate, lung, kidney and thyroid.2 Combine that history with back pain that is new, with unexplained weight loss, with pain that is constant and not relieved by rest or position change, or with pain that is markedly worse at night, and the picture needs investigating. We have written about night pain and when to worry in more detail.
Possible infection. Fever or chills with back pain; a recent bacterial infection, surgery or spinal procedure; intravenous drug use; or a suppressed immune system. Spinal infections are uncommon but can be slow to declare themselves and easy to miss.
Progressive neurological deficit. Leg weakness that is getting worse over days, a foot that drags or slaps, or numbness that is spreading rather than settling. Nerve root irritation from a disc is common and usually improves on its own. A deficit that is clearly worsening is a different matter and needs a medical opinion.
Pain that is not behaving like mechanical back pain. Most back pain changes with position and movement. Pain that is constant, unaffected by anything you do, and steadily worsening over weeks without a clear reason is worth a closer look even when no other flag is present.
What this means in practice
If you read that list and recognised nothing, you are in the large group whose back pain is painful but safe. The right approach for you is staying active, understanding that hurt does not mean harm, and getting good advice on graded movement. A thorough first visit for back pain at any good clinic should include these screening questions before anything else happens, and should repeat them if your symptoms change.
If you did recognise something, do not panic, but do not sit on it either. Most people with a red flag still turn out to have nothing serious. The point of asking is to make sure that the few who do are found quickly. Call your family doctor, go to a walk-in clinic, or, for the cauda equina symptoms above, go directly to the emergency department. Tell them your back hurts, and tell them exactly which symptom worried you.
References
- Hartvigsen J, Hancock MJ, Kongsted A, et al. What low back pain is and why we need to pay attention. Lancet. 2018;391(10137):2356-2367.
- Downie A, Williams CM, Henschke N, et al. Red flags to screen for malignancy and fracture in patients with low back pain: systematic review. BMJ. 2013;347:f7095.
- Finucane LM, Downie A, Mercer C, et al. International Framework for Red Flags for Potential Serious Spinal Pathologies. J Orthop Sports Phys Ther. 2020;50(7):350-372.
- Lavy C, James A, Wilson-MacDonald J, Fairbank J. Cauda equina syndrome. BMJ. 2009;338:b936.