Straight leg raise test: what it checks and what a positive result means

The straight leg raise test (SLR), sometimes called straight leg raising, is a standard part of the examination when someone has pain running from the lower back or buttock down the leg. NICE Clinical Knowledge Summaries (CKS) describe sciatica as radiating leg pain caused by compression or irritation of the lumbosacral nerve roots that form the sciatic nerve. Lifting the leg with the knee straight puts a stretch on those nerve roots, so if one is irritated the movement may bring on the familiar pain.

Nothing is injected and no scanner is involved. It is carried out by a clinician as part of a physical examination.

You are asked to lie flat on your back on an examination couch and relax. The clinician then lifts one leg, keeping the knee straight, and gradually bends the hip. CKS describes this as flexing the hip gradually with the knee extended, with the person lying supine.

You are asked to say when you feel pain and where it travels, because the useful finding is whether your familiar leg pain is brought on.

• Lie on your back with both legs straight.

• The clinician raises one leg slowly, knee straight.

• You report when pain starts and where it spreads.

• The clinician notes the angle at which your usual pain is brought on.

CKS states the test is positive if pain is reproduced below 60 degrees of hip flexion on the side being tested. In other words, pain that travels down the leg when the leg is lifted only a short way suggests irritation of a nerve root, most commonly from a disc problem. CKS notes a herniated disc causes about 90% of cases of sciatica.

The wording matters: the test is positive when the person's leg pain is reproduced, not simply when the movement feels tight or uncomfortable. That is why you are asked to describe what you feel and where it goes. The result is then read together with the history and the rest of the examination.

The straight leg raise is rarely used alone. CKS recommends a focused musculoskeletal and neurological examination: looking at the spine and posture, observing gait, checking range of movement, and testing for numbness, tingling, weakness or reduced reflexes in the area served by one nerve root. It also mentions other tests that may be considered, such as the femoral stretch test for upper lumbar disc problems and checking for an extensor plantar response.

CKS says investigations are not usually required unless there is diagnostic uncertainty or a serious underlying cause is suspected, and it advises not to routinely offer imaging to confirm the diagnosis. Most people with sciatica improve with conservative management within a few weeks to a few months, according to CKS, though recurrence is common. CKS says tests such as blood tests may be considered if infection, cancer or inflammatory conditions are suspected.

CKS lists red flags that suggest a serious condition: bowel or bladder dysfunction, severe or progressive weakness, saddle numbness, sudden bilateral nerve symptoms, immunosuppression, unexplained weight loss, a history of cancer and incapacitating or unrelenting night pain. The NHS tells people with sciatica on both sides, severe or worsening weakness or numbness in both legs, numbness around the genitals or bottom, or difficulty controlling the bladder or bowel to go to A&E or call 999.

For ordinary sciatica the NHS advises carrying on with normal activities where possible, gentle exercise and seeing a GP if symptoms have not improved after a few weeks, are getting worse or are stopping normal activity.