When should the straight leg raise (SLR) test be performed?

When to Perform the Straight Leg Raise Test

Perform the straight leg raise (SLR) test when evaluating any patient presenting with low back pain, leg pain, or combined back and leg pain to screen for lumbar disc herniation and nerve root compression. 1

Primary Clinical Indications

The SLR test should be performed in the following clinical scenarios:

• Suspected sciatica: When patients report pain radiating down the leg below the knee in the sciatic nerve distribution, suggesting nerve root compromise 1
• Low back pain with radicular symptoms: Any patient with back pain accompanied by leg symptoms that could indicate nerve root involvement 1
• Evaluation for lumbar disc herniation: As part of the initial assessment when disc herniation is in the differential diagnosis 1

Performing the Test as Part of Comprehensive Neurological Examination

The SLR should not be performed in isolation but rather as one component of a focused neurological assessment that includes:

• L4 nerve root evaluation: Test knee strength and knee reflexes 1
• L5 nerve root evaluation: Assess great toe and foot dorsiflexion strength 1
• S1 nerve root evaluation: Test foot plantarflexion and ankle reflexes 1
• Sensory distribution mapping: Document dermatomal sensory changes 1

Understanding Test Characteristics Before Ordering

Be aware of the test's diagnostic performance when deciding to use it:

• Standard SLR sensitivity: 91% (meaning it catches most cases of disc herniation with nerve root compression) but specificity is only 26% (many false positives) 1
• Crossed SLR test: Consider adding this variation, which has lower sensitivity (29%) but much higher specificity (88%), making it more confirmatory when positive 1
• Age-related limitation: Sensitivity decreases significantly with age, dropping below 50% in patients over 60 years old 1

When NOT to Rely Solely on SLR

Critical caveat: A negative SLR does not rule out sciatica or disc herniation, particularly in older patients. The diagnosis can be established by the combination of radicular pain pattern, dermatomal sensory changes, and motor weakness in a nerve root distribution even without a positive SLR. 1

Enhanced Testing Approach

Consider performing extended variations for improved diagnostic accuracy:

• Extended SLR (ESLR): Add hip internal rotation or ankle dorsiflexion at the point where symptoms first emerge during standard SLR to better differentiate neural from musculoskeletal causes, which shows almost perfect inter-rater reliability (Cohen's Kappa 0.85) 2
• Slump test: Use this seated variant when standard SLR is negative but clinical suspicion remains high, as it has higher sensitivity (84% vs 52%) for detecting disc herniations 3

Timing Relative to Imaging Decisions

The SLR test helps determine imaging urgency:

• Positive SLR with red flags: Proceed immediately to MRI if severe or progressive neurological deficits, suspected cauda equina syndrome (check for urinary retention), or other serious pathology indicators are present 4, 5
• Positive SLR without red flags: Manage conservatively initially; reserve imaging for persistent symptoms after 4-6 weeks 4, 5
• Persistent positive SLR at 4-6 weeks: This is an indication for delayed imaging and potential specialist referral 4, 5

Common Pitfalls to Avoid

• Over-reliance on the test: Do not use SLR as the sole diagnostic criterion; it must be interpreted alongside the complete clinical picture and imaging when treatment decisions are being made 1, 5
• Ignoring false negatives: Remember that 9-48% of true sciatica cases may have negative SLR, especially in elderly patients 1
• Misinterpreting positive results: With only 26% specificity, many positive tests are false positives; confirm with other clinical findings 1
• Missing crossed SLR: Failing to perform the crossed SLR test means missing a highly specific (88%) finding that strongly indicates disc herniation and predicts poor response to conservative management 1, 6