Low back pain is the leading cause of disability worldwide, primarily affecting the working population (ages 35-55). In fact, back pain is in the top five most common reasons people seek emergency care, and 50-80 percent of people will experience a bout of back pain at least once in their lives.
In primary care, about one to five percent of patients who present with back pain are considered to have a serious condition, either stemming from fracture, malignancy, infection, inflammation, neurological causes (such as, cauda equina, radiculopathy, or spinal stenosis), or vascular conditions, such as ruptured aortic aneurysm.
“Red Flags” to Look for During Clinical Assessment of Acute Low Back Pain
It is crucial to identify serious causes of acute low back pain during the history and physical exam to more quickly identify conditions that require urgent attention or additional workup. Clinical practice guidelines typically recommend looking for warning signs (“red flags”) as a reasonable way to help accomplish this. The table below shows the likelihood of specific etiologies based on commonly used findings.
| Findings | Possible Etiologies | +Likelihood Ratio | |
| Red flags recommended by most clinical practice guidelines | History of malignancy | Cancer | 14.7 |
| Unexpected weight loss | Cancer | 2.7 | |
| Significant trauma relative to age | Fracture | 10 | |
| Prolonged use of corticosteroids | Fracture | 48.5 | |
| Fever | Infection | Not calculated | |
| Other commonly used red flags | Age > 70 years | Fracture, cancer, vascular disease, infection | 11.2 |
| Failure to improve after 1 month | Varied; Refer to specialist recommended | 3 | |
| Motor neurological deficit | Cord or nerve root compression | Not calculated | |
| Urinary retention or bowel incontinence, saddle anesthesia | Cauda equina syndrome | Not calculated | |
| Contusion, abrasion | Fracture | 31 | |
| Known history of AAA | Ruptured AAA | Not calculated | |
| History of recent spinal procedure | Infection | Not calculated | |
| Immunocompromise, HIV, IV drug use | Epidural abscess, metastatic disease, osteomyelitis, discitis | Not calculated | |
| Abbreviations: AAA = Abdominal Aortic Aneurysm; HIV = Human Immunodeficiency Virus; IV = Intravenous | |||
In addition to these warning signs, consider other factors that, while they may not make it into the red flag list above, still increase the risk of experiencing serious back pain. Such risk factors include a history of osteoporosis (think: fracture), having constant unrelenting back pain that is not affected by one’s positioning (think: cancer or other internal disorder), nocturnal pain (think: cancer), anticoagulant use (think: internal bleed), and morning stiffness which improves with activity or exercise (think: an autoimmune condition).
Distinguishing between mechanical and inflammatory back pain
Because mechanical back pain (injury to the spine, disks, or surrounding soft tissue) can sometimes mask inflammatory back pain, which is treated differently, it is important to differentiate between the two. The table below illustrates crucial differences.
| Feature | Mechanical back pain | Inflammatory back pain |
| Onset | Variable, may be acute | Insidious |
| Age | Any; most commonly middle age, working adults | Typically < 40 years |
| Response to exercise | May worsen pain | Improves pain |
| Response to rest | Improves pain | No improvement in pain |
| Nocturnal symptoms | Mild | Moderate (improves after getting up) |
| Systemic disease | No | Yes |
| References: Rheumatol Ther. 2020 Dec; 7(4): 667-684, American College of Physicians (ACP) 2024 conference presentation in Boston, MA by Dr. Kimberly A. Lyn Shue. | ||
When to Obtain Imaging Studies and Lab Work
Acute low back pain typically resolves within six weeks of the initial onset; therefore, imaging is not routinely recommended for these patients. However, if a serious condition is suspected, such as when red flags are identified or if imaging findings will change management, then imaging should be performed.
X-ray is indicated in patients with a history of trauma, osteoporosis, chronic corticosteroid use, suspicion of spondylolysis, or inflammatory arthritis.
Magnetic resonance imaging (MRI) is preferred for patients with red flags, neurological conditions, and persistent or progressive symptoms following conservative management where diagnostic uncertainty exists.
For patients with suspected cauda equina syndrome or progressive neurological decline, MRI without contrast is indicated. For patients with a history of intravenous drug use, concern for infection, malignancy, or immunosuppression, MRI with and without contrast is indicated.
Computed tomography (CT) is helpful in the diagnosis of fractures, dislocations, spondylolisthesis, scoliosis, stenosis, and tumors. For patients who cannot have MRI imaging, CT myelography is useful as a second choice, such as in cases of progressively worsening neurological function and suspicion of cauda equina syndrome.
Laboratory assessment is indicated if there is a concern for systemic disease and should be guided by the history and physical exam. Erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and complete blood count (CBC) are helpful to assess for inflammatory and infectious disease. Urinalysis, liver function tests, and lipase are helpful to evaluate extraspinal back pain etiologies. Calcium and alkaline phosphatase elevations are associated with higher bone turnover and may be an indication of spinal malignancy.
To identify potentially life-threatening and serious causes of back pain, it is vital to rule out red flags and risk factors during the history and physical exam. Imaging should then be performed for red flags or if imaging findings will change management. Perform laboratory testing based on suspicion of systemic disease from the history and physical exam. Following these steps will improve the odds of diagnosing serious causes of back pain.
