CRPS (complex regional pain syndrome) is diagnosed primarily through a clinical evaluation, not a single lab test or scan. Doctors use a standardized set of criteria called the Budapest Criteria, which require a specific pattern of symptoms you report and signs they can observe during an exam. Because no blood test or imaging study can confirm CRPS on its own, getting the right diagnosis often depends on seeing a clinician who knows what to look for.
The Budapest Criteria: The Diagnostic Standard
The Budapest Criteria are the internationally accepted framework for diagnosing CRPS. They were developed to replace older, less precise guidelines and remain the current standard endorsed by the International Association for the Study of Pain (IASP). To meet the criteria, you need to check four boxes.
First, you must have ongoing pain that is out of proportion to whatever injury or event triggered it. A minor sprain causing months of burning, searing pain in the entire hand, for example, would qualify. Second, you must report at least one symptom in each of four categories:
- Sensory: heightened pain sensitivity, or pain from things that shouldn’t hurt (like a light touch or a breeze on the skin)
- Vasomotor: skin color changes, temperature differences, or the affected limb feeling noticeably warmer or cooler than the other side
- Sudomotor/edema: swelling, or changes in sweating patterns on the affected limb
- Motor/trophic: reduced range of motion, weakness, tremor, or changes in hair, nail, or skin growth
Third, the clinician must be able to observe at least one physical sign in two or more of those same four categories during the exam. This is what separates a clinical diagnosis from a research one: research criteria require signs in three or more categories, making them stricter. Fourth, and critically, no other diagnosis can better explain what’s happening. CRPS is partly a diagnosis of exclusion.
What the Physical Exam Looks Like
During the exam, your doctor will compare the affected limb to the unaffected one. They’re looking for visible and measurable differences. Skin color is one of the first things assessed: the affected side may appear red, blue, or mottled compared to the other. They’ll feel both limbs to check for temperature differences. A gap of more than 1°C (about 1.8°F) between limbs is considered a positive finding, and some research suggests that a 2°C difference yields even stronger diagnostic accuracy, with 73% sensitivity and 94% specificity.
To test sensory changes, the clinician will lightly touch the skin, apply a pinprick, or press on deeper tissues and joints. They’re checking for two things: allodynia (pain from stimuli that normally don’t hurt, like a cotton swab brushed across the skin) and hyperalgesia (an exaggerated pain response to something mildly painful, like a pinprick). They’ll also measure range of motion in the affected joints, look for swelling, and note any changes in how hair or nails are growing on that limb. Nails may appear ridged, brittle, or grow at a different rate. Skin may look shiny or thin.
Type 1 vs. Type 2 CRPS
CRPS is classified into two types based on whether a specific nerve was injured. Type 1, which accounts for about 90% of cases, develops after an illness or injury that didn’t directly damage a nerve. A fracture, surgery, or even a sprain can trigger it. Type 2 occurs after a confirmed nerve injury, but the symptoms must spread beyond the territory of the damaged nerve. If pain and other signs stay limited to the area that one nerve supplies, that’s more likely neuropathic pain from the nerve injury itself rather than CRPS.
A 2019 expert workshop also introduced a third classification: “CRPS with Remission of Some Features.” This applies to people who previously met full diagnostic criteria but now show fewer signs, even though their pain and functional limitations may not have improved. This distinction matters because it prevents those patients from losing their diagnosis entirely when some visible signs fade.
Tests That Support the Diagnosis
While no single test confirms CRPS, several can provide supporting evidence and help rule out other conditions.
Triple-Phase Bone Scan
This imaging study tracks blood flow and bone metabolism in the affected limb across three phases. It’s highly specific for CRPS, meaning that when it’s positive, it strongly supports the diagnosis. Specificity ranges from 83% to 100% in studies of upper extremity CRPS. The catch is low sensitivity: only 31% to 50% of people with CRPS will show a positive result. So a negative bone scan does not rule CRPS out.
Sweat Testing (QSART)
Quantitative sudomotor axon reflex testing measures how your sweat glands respond to a mild electrical stimulus. It evaluates the part of the nervous system that controls sweating, which is often disrupted in CRPS. The test compares sweat output between the affected and unaffected limbs. Asymmetry in sweat production provides objective evidence of autonomic nervous system dysfunction.
Infrared Thermography
This uses a thermal camera to map skin temperature across both limbs with precision. It can detect temperature asymmetry more accurately than a clinician’s hand, and it creates a visual record that can be tracked over time.
X-rays or MRI may also be ordered, not to diagnose CRPS directly, but to look for bone density changes (patchy osteoporosis can develop in the affected limb) or to rule out fractures, infections, or other structural problems.
Conditions That Must Be Ruled Out
Because the Budapest Criteria require that no other diagnosis better explains the symptoms, your doctor needs to consider several conditions that can mimic CRPS. Deep vein thrombosis can cause limb swelling, warmth, and pain. Cellulitis, a skin infection, produces redness, heat, and tenderness. Lymphedema causes chronic swelling. Peripheral neuropathy, both small-fiber and large-fiber types, can produce burning pain and sensory changes. Raynaud phenomenon causes color changes and temperature shifts in the extremities. Vascular insufficiency and vasculitis can also overlap with some CRPS features.
Blood tests, nerve conduction studies, ultrasound for clots, and other targeted investigations help eliminate these possibilities. The process can feel frustrating, but ruling out mimics is what makes a CRPS diagnosis reliable.
Why Early Diagnosis Matters
CRPS treatment is most effective when started early. The National Institute of Neurological Disorders and Stroke emphasizes that anyone with new, disproportionate limb pain should be evaluated as soon as possible, even if there’s no known trauma. Early intervention with physical therapy, pain management, and psychological support can significantly improve outcomes. Delays in diagnosis, which are common because many clinicians rarely encounter CRPS, allow the condition to become more entrenched and harder to treat.
If you suspect CRPS, seeking out a pain specialist, neurologist, or rehabilitation physician with experience in the condition can shorten the path to diagnosis. Bringing a written timeline of your symptoms, noting which categories they fall into, can help the evaluation go more smoothly.