Lachman test: technique, grading and accuracy

For physical therapists and other clinicians examining knee injuries: the Lachman test checks the anterior cruciate ligament by pulling the tibia forward on a stabilized femur at 20 to 30 degrees of knee flexion. Grade the side-to-side translation and the endpoint; pooled studies put its sensitivity near 0.81 and specificity near 0.85.⁠^1,2

What does the Lachman test assess and when is it used?

It assesses the anterior cruciate ligament by measuring anterior tibial translation and the quality of its endpoint, and it is recommended whenever an ACL injury is suspected.⁠^5,8 Wroble and Lindenfeld called it the clinical standard for assessing increased anterior tibial translation, and Mulligan and colleagues describe it as the most direct and definitive technique for the ACL.⁠^1,8

Timing matters. The test is best performed before the patient’s pain, swelling and guarding develop.⁠¹ In a meta-analysis of acute complete ACL ruptures, the Lachman test’s sensitivity was 0.81 in the office and 0.91 under anesthesia, and a later review found lower accuracy in post-acute presentations.⁠^2,9

Who should examine an ACL injury with the Lachman test?

A clinician trained in the knee examination, physical therapists among them: in the endpoint and prone Lachman studies on this page, physical therapists performed every test.⁠^1,6

How do you perform the Lachman test step by step?

With the patient supine on a firm table, the knee flexed 20 to 30 degrees and the hamstrings relaxed, stabilize the distal thigh with one hand and pull the proximal tibia forward with the other, testing the uninvolved knee first.⁠¹ The steps below follow the protocol two physical therapists used in a 2015 diagnostic accuracy study.⁠¹

1. Position the patient. Supine on a firm examination table, both knees flexed to 20 to 30 degrees, and the same angle on each side.⁠¹
2. Start with the uninvolved knee. It sets the baseline against which the injured knee is judged.⁠¹
3. Stabilize the femur. The upper hand holds the unsupported distal thigh.⁠¹
4. Place the tibial hand. The lower hand grips the proximal tibia with the thumb on the anterior joint line and the fingers feeling that the hamstrings are relaxed.⁠¹
5. Apply the anterior pull. Pull the tibia forward on the fixed femur; the study examiners used approximately 30 pounds of force.⁠¹
6. Judge translation and endpoint. Note the amount of forward movement and whether it stops suddenly (firm) or not (soft, absent or ill-defined).⁠¹
7. Repeat on the injured knee and compare. Grade the side-to-side difference and record the endpoint before any other ligament test, so later findings do not bias the grade.⁠¹

How much force and knee flexion does the Lachman test use?

Twenty to 30 degrees of knee flexion and, in the 2015 endpoint study, approximately 30 pounds of anterior pull.⁠¹ The same study measured instrumented translation with a KT-1000 arthrometer at 15, 20 and 30 pounds, and the drop leg version uses 25 degrees of flexion.⁠^1,7 Instrumented testing has its own accuracy: in a meta-analysis of acute ACL ruptures, the KT-1000 with maximum manual force had a sensitivity and a specificity of 0.93.⁠¹⁰

How is the Lachman test graded for translation and endpoint?

By two separate judgments: the amount of anterior translation compared with the other knee, and the quality of the endpoint, firm or soft.⁠^1,3 The form of the International Knee Documentation Committee (IKDC), founded in 1987 by knee surgeons from Europe and America, qualifies each examination finding as normal, nearly normal, abnormal or severely abnormal, and the ligament examination is one of its four evaluated problem areas.⁠¹¹

The letters A to D for the four IKDC categories follow published reports of the IKDC objective score.⁠⁴ Some studies use a different, absolute scale instead. The 2015 endpoint study graded translation as I (less than 5 mm), II (5 to 10 mm) or III (more than 10 mm), and the endpoint as A (firm, sudden) or B (absent, ill-defined or softened).⁠¹ The two systems both use the letter A, so a note should say which scale it uses.

What does a soft or absent endpoint mean on the Lachman test?

A soft or absent endpoint points to loss of the ACL’s restraint, while a firm endpoint signifies a normal ACL in the view Mulligan and colleagues summarize.⁠¹ A firm endpoint with increased translation may represent a partial tear or a tear of the posterolateral bundle.⁠¹ Their rule of thumb is to give more weight to the quality of motion and the distinctness of the endpoint than to the amount of laxity, especially when the uninvolved knee is itself lax.⁠¹

How reliable is the Lachman endpoint between examiners?

In the 2015 study, two physical therapists agreed on a firm or soft endpoint 91% of the time (kappa 0.72), but on the amount of translation only 65% of the time (weighted kappa 0.52).⁠¹ Earlier work the authors reviewed found wider spread: physical therapists’ intertester kappa ranged from 0.02 to 0.69.⁠¹ The endpoint grade alone had a sensitivity of 0.81 with perfect specificity in that study’s 45 patients, 17 of whom had a torn ACL.⁠¹

What are the Lachman test sensitivity and specificity?

The most recent pooled estimate is a sensitivity of 81% and a specificity of 85%, from a 2022 bivariate meta-analysis of ACL tears without other ligament injury.⁠² Earlier reviews reported higher figures, and the estimate falls for complete tears and for post-acute presentations.⁠^2,5

"Calc." marks likelihood ratios calculated from the published pair as sensitivity / (1 − specificity) and (1 − sensitivity) / specificity; "rep." marks the study’s own.⁠¹² The special test interpretation guide shows how to turn these ratios into a post-test probability for a given patient.

Why is the Lachman test less accurate in newer meta-analyses?

Because the 2022 review excluded tears with other ligament injuries and used a bivariate model, and its authors argue that earlier pooling methods ignored the link between sensitivity and specificity and so overestimated accuracy.⁠² They conclude that the test’s accuracy, particularly after the acute phase and for complete tears, is lower than previously reported.⁠² The 2006 review’s own studies were heterogeneous, which is a second reason to prefer the narrower, newer estimate when the patient matches it.⁠⁵

How does Lachman compare with pivot shift and drawer?

In the 2022 review, the anterior drawer had a sensitivity of 83% and a specificity of 85%, and the pivot shift 55% and 94%, so the pivot shift is the stronger test for ruling a tear in.⁠² For acute complete ruptures examined in the office, the Lachman test had the highest sensitivity of the three, and all three had comparable specificity.⁠⁹

What are the prone, drop-leg and stabilized Lachman variations?

They are positions that change how the examiner holds the thigh, each proposed to make the test easier to perform or to read.⁠^6,7,8 Only the prone version has its own published diagnostic accuracy against arthroscopy and clinical consensus among the sources cited here.⁠⁶

When is the prone or drop leg Lachman the better choice?

When the examiner cannot stabilize the thigh well, as with a large limb and small hands, which is the rationale the prone study gives.⁠⁶ Adler and colleagues describe the drop leg version as physically easier to perform than the standard test and sensitive for anterior laxity.⁠⁷ Because the prone test’s sensitivity was 70%, a negative prone result should be paired with other findings rather than used alone to exclude a tear.⁠⁶

What are the most common Lachman test pitfalls?

Guarding, a late examination, uneven knee angles, ignoring the other knee’s laxity and missing a posterior cruciate injury account for most misleading results.⁠^1,9 Each has a fix in the protocols cited on this page:

• Hamstring guarding. The fingers of the tibial hand check that the hamstrings are relaxed before the pull.⁠¹ In acute ruptures, sensitivity rose from 0.81 in the office to 0.91 under anesthesia.⁠⁹
• Testing late. The test reads best before pain, swelling and guarding develop.⁠¹
• Different angles on each side. Both knees should be at the same degree of flexion.⁠¹
• Skipping the uninvolved knee. Testing it first sets the baseline, and it matters most when the uninvolved knee is itself lax.⁠¹
• Missing a posterior cruciate injury. The endpoint study excluded suspected posterior cruciate involvement and screened for it with a tibial sag sign at 90 degrees of flexion before the Lachman test.⁠¹
• Small hands, large thigh. An unstable grip on the femur is the problem the prone and drop leg versions address.⁠^6,7
• Reading a negative test as a rule-out. With a pooled negative likelihood ratio near 0.22, a negative Lachman lowers the probability of a tear without excluding it.⁠^2,13

How do you screen for a PCL injury before the Lachman test?

Look and feel for a posterior tibial sag with the knee at 90 degrees, then use the quadriceps active drawer if the step-off looks reduced, as the 2015 endpoint study did before every Lachman test.⁠¹ In that protocol, a tibial plateau less than one centimeter anterior to the femoral condyle prompted the quadriceps active drawer, in which the patient gently contracts the quadriceps with the foot stabilized on the table.⁠¹ The study cites a sensitivity of 0.90 and a specificity of 0.99 for palpable loss of the step-off, and a specificity of 96% with a sensitivity of 53% for the quadriceps active drawer.⁠¹

Can a partial ACL tear give a firm Lachman endpoint?

Yes. A firm endpoint in the presence of increased translation may represent a partial tear or a tear of the posterolateral bundle.⁠¹ The 2022 review called for more research on the test in partial tears and acute presentations.⁠²

How do you interpret a positive Lachman test for one patient?

Start from the patient’s pretest probability, choose the accuracy figures from the study population that matches the presentation, and apply the likelihood ratio; post-acute presentations call for the lower post-acute figures.⁠^2,13 Post-test odds are the pretest odds multiplied by the likelihood ratio.⁠¹³

The sensitivity and specificity are the 2022 review’s post-acute and overall estimates; the patient and the pretest estimate are invented inputs.⁠² The special test interpretation guide sets out the same arithmetic step by step.

Does a positive pivot shift add to a positive Lachman test?

It adds the stronger evidence for ruling a tear in: in the 2022 review the pivot shift’s specificity was 94%, against 85% for the Lachman test, and its authors named the pivot shift the best test overall for ruling a tear in.⁠² The 2006 review likewise recommended doing both, the Lachman test for its accuracy and the pivot shift for its specificity.⁠⁵

How should Lachman test findings be documented?

Record the position and knee angle, the side tested first, the translation grade with the scale named, the endpoint, any guarding and the impression, so a later examiner can repeat the test the same way.⁠^1,3 Instrumented values belong in the note with the device and the force used, since the arthrometer’s accuracy changes with force.⁠¹⁰

What should be repeated at a follow-up examination?

The same version of the test, at the same angle and on the same scale, so any change reflects the knee and not the method.⁠¹ For progress documentation in a plan of care, the PT reassessment guide covers what Medicare expects in a progress report.

How does the Lachman test fit with the rest of the knee exam?

As the most sensitive of the three manual ACL tests in office examinations of acute ruptures, read alongside the more specific pivot shift and the history.⁠^2,9 The 2006 review recommended performing the Lachman test when an ACL injury is suspected, and the pivot shift as well because of its high specificity.⁠⁵ Instrumented laxity testing adds a measured side-to-side difference where the device is available.⁠¹⁰

Can the Lachman test be used with children and adolescents?

It is used with them, but the accuracy studies cited here enrolled adults and older teenagers, aged 16 to 57 and 20 to 64 in the two physical therapist studies.⁠^1,6 A pediatric outcome study graded Lachman results by the IKDC bands after surgery in a cohort whose fracture-fixation group was aged 7 to 15, which shows the grading in use rather than its diagnostic accuracy in children.⁠³

For patients and families who need a clinic after the examination, the ACL reconstruction guide is written for them. The clinical resources library holds the other examination references.

Sources

1. Mulligan EP, McGuffie DQ, Coyner K, Khazzam M. The reliability and diagnostic accuracy of assessing the translation endpoint during the Lachman test (Int J Sports Phys Ther 2015;10(1):52-61; PMID 25709863; PMC4325288; full text as shown on PubMed Central). Checked October 30, 2026.
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   “The Lachman test is characterized as the most direct and definitive evaluative technique used to determine the status of the ACL and is best performed prior to the onset of the patient’s pain, swelling, and guarding.”; “Traditionally, a grade of A is given when the endpoint is perceived to be “firm” while a grade of B is given if the endpoint is felt to be soft, absent, or ill‐defined.”; “A firm endpoint in the presence of increased translation may represent a partial tear or a tear of the ACL’s posterolateral bundle.”; “Callaghan et al 12 suggest that an absent or soft endpoint indicates the lack of anterior restraint, whereas a firm endpoint signifies a normal ACL.”; “17 of the 45 patients had a torn ACL.”; “This classification was determined prior to testing for a pivot shift so as to not bias the findings of the examiners.”; “For all patients the uninvolved knee was evaluated first in order to establish a baseline by which the contralateral knee could be judged.”; “This is an important element of the evaluative process particularly in cases where there is significant inherent laxity of the uninvolved extremity.”; “The general “rule of thumb” for interpreting ligamentous stability is to place more value on the quality of motion and endpoint distinctiveness as compared to the amount of laxity present.”; “When analyzed by discipline, physical therapists had an intertester kappa coefficient range of 0.02 to 0.69 with 53‐84% agreement.”; “suspicion of posterior cruciate ligament (PCL) involvement”; “PCL injury evaluation was conducted via visual and palpatory assessment of a tibial sag sign with knee flexed at 90 degrees.”; “If the tibial plateau did not appear to be at least one centimeter (cm) anterior to the femoral condyle, a quadriceps active drawer test was applied to rule in PCL injury.”; “The palpatory loss of the tibia‐femur step‐off relationship has been shown to be a sensitive (0.90) and specific (0.99) means by which to detect the presence of a PCL injury.”; “The quadriceps active drawer test is performed by the patient gently contracting the quadriceps with the knee flexed at 90° and foot stabilized on the treatment plinth.”; “The specificity of this maneuver has been reported to be 96% and the sensitivity 53%.”; “record the millimeters of anterior translation at 15, 20, and 30 pounds (6.8, 9.1, and 13.6 kg) of force”; “The test was performed with the patient lying supine on a firm examination table and the knee flexed to 20‐30 degrees. Care was taken to ensure the both knees were in the same degree of flexion during the physical examination procedure.”; “The examiner’s upper hand stabilized the unsupported distal thigh, while the lower hand, with the thumb on the anterior joint line, and the fingers feeling to ensure that the hamstrings were relaxed, pulled the tibia forward with approximately 30 lbs of force.”; “I < 5 mm translation II 5 – 10 mm translation III > 10 mm translation”; “Forty‐five consecutive patients with a complaint of knee pain were independently evaluated for the endpoint classification during a Lachman test by two physical therapists before any other diagnostic assessment.”; “The 21 men and 24 women ranged in age from 20 to 64 years”; “The agreement between examiners on A versus B endpoint classification was 91% with a kappa coefficient of 0.72. In contrast, classification agreement based on the translational amount had an agreement of 65% with a weighted kappa coefficient of 0.52.”; “The sensitivity of the endpoint grade alone was 0.81 with perfect specificity resulting in a positive likelihood ratio of 6.2 and a negative likelihood ratio of 0.19.”.
2. Sokal PA, Norris R, Maddox TW, Oldershaw RA. The diagnostic accuracy of clinical tests for anterior cruciate ligament tears are comparable but the Lachman test has been previously overestimated: a systematic review and meta-analysis (Knee Surg Sports Traumatol Arthrosc 2022;30(10):3287-3303; DOI 10.1007/s00167-022-06898-4; PMID 35150292; PMC9464183; full text as shown on PubMed Central). Checked October 30, 2026.
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   “The aim of this study was to report the diagnostic accuracy of clinical tests for anterior cruciate ligament tears (partial and complete) without concomitant knee ligament injury.”; “Meta-analyses have also been performed using methods that do not account for the non-independence of sensitivity and specificity, potentially overestimating diagnostic accuracy.”; “anterior drawer test 83% [95% CI, 77–88] and 85% [95% CI, 64–95]; Lachman test 81% [95% CI, 73–87] and 85% [95% CI, 73–92]; pivot shift test 55% [95% CI, 47–62] and 94% [95% CI, 88–97]”; “complete tears 68% [95% CI, 54–79] and 79% [95% CI, 51–93]; post-acute injuries 70% [95% CI, 57–80] and 77% [95% CI, 53–91]”; “The diagnostic accuracy of the Lachman test, particularly in post-acute presentations and for complete tears, is lower than previously reported.”; “The pivot shift and Lever sign were the best tests overall for ruling in or ruling out an anterior cruciate ligament tear, respectively.”; “Further research is required to establish more accurate estimates for the Lachman test in acute presentations and partial ligament tears using bivariate analysis.”.
3. Melugin HP, Desai VS, Camp CL, Milbrandt TA, Dahm DL, Levy BA, Stuart MJ, Krych AJ. Do tibial eminence fractures and anterior cruciate ligament tears have similar outcomes? (Orthop J Sports Med 2018;6(12):2325967118811854; DOI 10.1177/2325967118811854; PMID 30547044; PMC6287315; full text as shown on PubMed Central; methods section). Checked October 30, 2026.
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   “Examination results were reported based on the IKDC criteria. For Lachman testing, compared with the contralateral knee, grading was as follows: 0, normal (–1 to 2 mm); 1+, nearly normal (3 to 5 mm); 2+, abnormal (6 to 10 mm); and 3+, severely abnormal (>10 mm).”; “20 patients (11 male, 9 female; mean age, 11.9 years [range, 7-15 years]) who underwent surgical fixation for a TEF were matched to a group of 40 patients”.
4. Ferretti A, Monaco E, Wolf MR, Guzzini M, Carli A, Mazza D. Surgical treatment of Segond fractures in acute anterior cruciate ligament reconstruction (Orthop J Sports Med 2017;5(10):2325967117729997; DOI 10.1177/2325967117729997; PMID 29051899; PMC5637969; full text as shown on PubMed Central; methods section). Checked October 30, 2026.
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   “The International Knee Documentation Committee (IKDC) evaluation system was included to assess the patients’ subjective evaluation of knee function, such as symptoms and activity level, as well as objective measures such as knee laxity and range of motion (ROM) examinations”; “The results of the IKDC objective score were graded as A (normal), B (nearly normal), C (abnormal), or D (severely abnormal).”.
5. Benjaminse A, Gokeler A, van der Schans CP. Clinical diagnosis of an anterior cruciate ligament rupture: a meta-analysis (J Orthop Sports Phys Ther 2006;36(5):267-288; DOI 10.2519/jospt.2006.2011; PMID 16715828; abstract as shown on Europe PMC). Checked October 30, 2026.
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   “compared the performance of the clinical examination of the knee with a reference standard, such as arthroscopy, arthrotomy, or MRI”; “Twenty-eight studies that assessed the accuracy of clinical tests for diagnosing ACL ruptures met the inclusion criteria. Study results were, however, heterogeneous.”; “The Lachman test is the most valid test to determine ACL tears, showing a pooled sensitivity of 85% (95% confidence interval [CI], 83-87) and a pooled specificity of 94% (95% CI, 92-95).”; “The pivot shift test is very specific, namely 98% (95% CI, 96-99), but has a poor sensitivity of 24% (95% CI, 21-27).”; “The anterior drawer test shows good sensitivity and specificity in chronic conditions, respectively 92% (95% CI, 88-95) and 91% (95% CI, 87-94), but not in acute conditions.”; “In case of suspected ACL injury it is recommended to perform the Lachman test. Because the pivot shift test is very specific both in acute as well as in chronic conditions, it is recommended to perform the pivot shift test as well.”.
6. Mulligan EP, Harwell JL, Robertson WJ. Reliability and diagnostic accuracy of the Lachman test performed in a prone position (J Orthop Sports Phys Ther 2011;41(10):749-757; DOI 10.2519/jospt.2011.3761; PMID 21891874; abstract as shown on Europe PMC). Checked October 30, 2026.
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   “An alternative position for evaluating the integrity of the ACL has been proposed as a means for examiners with smaller hands to adequately stabilize the thigh of a larger individual”; “Direct arthroscopic visualization and a consensus of clinical findings, including joint arthrometry and magnetic resonance imaging, were used as the reference standards.”; “Fifty-two consecutive patients with a complaint of knee pain were independently evaluated in a prone position for the status of their ACL by 2 physical therapists”; “The 31 men and 21 women ranged in age from 16 to 57 (mean ± SD, 34.3 ± 4.2) years”; “The agreement between examiners was 90%, with a kappa coefficient of 0.81.”; “The sensitivity of the prone Lachman test was 70% and the specificity was 97%, resulting in a positive likelihood ratio of 20.17 and a negative likelihood ratio of 0.32.”; “the test should not be used as the sole criterion to rule out the presence of the injury.”.
7. Adler GG, Hoekman RA, Beach DM. Drop leg Lachman test. A new test of anterior knee laxity (Am J Sports Med 1995;23(3):320-323; DOI 10.1177/036354659502300312; PMID 7661260; abstract as shown on Europe PMC). Checked October 30, 2026.
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   “This test is performed with the patient supine and the leg to be examined abducted off the side of the table and flexed 25 degrees.”; “The thigh is stabilized to the examining table with one of the examiner’s hands, and the patient’s foot is held between the examiner’s legs.”; “A prospective study of 52 patients who were identified as unilaterally anterior cruciate ligament deficient was conducted.”; “In the conscious group, the drop leg Lachman test resulted in 1.8 mm greater average excursion than the Lachman test.”; “In the anesthetized group, the drop leg Lachman test resulted in 2.4 mm more average translation than the Lachman test.”; “The drop leg Lachman test is physically easier to perform than the Lachman test, and it is a sensitive method of demonstrating anterior laxity in an anterior cruciate ligament-deficient knee.”.
8. Wroble RR, Lindenfeld TN. The stabilized Lachman test (Clin Orthop Relat Res 1988;(237):209-212; PMID 3191631; abstract as shown on Europe PMC). Checked October 30, 2026.
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   “While the Lachman test is the clinical standard for assessing increased anterior tibial translation, it has some drawbacks.”; “Problems remain with quantitation, reproducibility, and execution. The authors report on modifications designed to solve these problems.”; “The modifications are comfortable for patients, reliable, and can be performed on limbs of all sizes.”.
9. van Eck CF, van den Bekerom MP, Fu FH, Poolman RW, Kerkhoffs GM. Methods to diagnose acute anterior cruciate ligament rupture: a meta-analysis of physical examinations with and without anaesthesia (Knee Surg Sports Traumatol Arthrosc 2013;21(8):1895-1903; DOI 10.1007/s00167-012-2250-9; PMID 23085822; abstract as shown on Europe PMC). Checked October 30, 2026.
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   “All cross-sectional and cohort studies comparing one or more physical examination tests for diagnosing acute complete ACL rupture to an accepted reference standard such as arthroscopy, arthrotomy and MRI were included.”; “Twenty studies were identified and included. The overall sensitivity of the Lachman test was 0.81 and the specificity 0.81; with anaesthesia, the sensitivity was 0.91 and the specificity 0.78.”; “For the anterior drawer test, the sensitivity was 0.38 and the specificity 0.81; with anaesthesia, the sensitivity was 0.63 and the specificity 0.91.”; “The sensitivity of the pivot shift test was 0.28 and the specificity 0.81; with anaesthesia, the sensitivity was 0.73 and the specificity 0.98.”; “In the office setting, the Lachman test has the highest sensitivity for diagnosing an acute, complete ACL rupture, while all three tests had comparable specificity.”.
10. van Eck CF, Loopik M, van den Bekerom MP, Fu FH, Kerkhoffs GM. Methods to diagnose acute anterior cruciate ligament rupture: a meta-analysis of instrumented knee laxity tests (Knee Surg Sports Traumatol Arthrosc 2013;21(9):1989-1997; DOI 10.1007/s00167-012-2246-5; PMID 23073818; abstract as shown on Europe PMC). Checked October 30, 2026.
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    “The sensitivity of the KT 1000 Arthrometer with 69 N was 0.54. With 89 N, the sensitivity was 0.78 and the specificity 0.92, and with maximum manual force, the sensitivity was 0.93 and the specificity 0.93.”; “The KT Arthrometer performed with maximum manual force has the highest sensitivity, specificity, accuracy and positive predictive value for diagnosing ACL rupture.”.
11. Hefti F, Müller W, Jakob RP, Stäubli HU. Evaluation of knee ligament injuries with the IKDC form (Knee Surg Sports Traumatol Arthrosc 1993;1(3-4):226-234; DOI 10.1007/BF01560215; PMID 8536037; abstract as shown on Europe PMC). Checked October 30, 2026.
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    “For evaluation there are four problem areas (subjective assessment, symptoms, range of motion and ligament examination).”; “a group of knee surgeons from Europe and America met in 1987 and founded the International Knee Documentation Committee (IKDC).”; “Each parameter is qualified as "normal", "nearly normal", "abnormal" or "severely abnormal".”.
12. Pewsner D, Battaglia M, Minder C, Marx A, Bucher HC, Egger M. Ruling a diagnosis in or out with “SpPIn” and “SnNOut”: a note of caution (BMJ 2004;329(7459):209-213; DOI 10.1136/bmj.329.7459.209; PMID 15271832; PMC487735; full text as shown on PubMed Central). Checked October 30, 2026.
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    “Sensitivity —The proportion of people with the disease who are correctly identified by a positive test result (“true positive rate”)”; “Specificity —The proportion of people free of the disease who are correctly identified by a negative test result (“true negative rate”)”; “Likelihood ratio of a positive test result (LR +)—The ratio of the true positive rate to the false positive rate: sensitivity/(1-specificity)”; “Likelihood ratio of a negative test result (LR -)—The ratio of the false negative to the true negative rate: (1-sensitivity)/specificity”; “Pretest probability (prevalence) —The probability that an individual has the target disorder before the test is carried out”; “Pretest odds —The odds that an individual has the target disease before the test is carried out (pretest probability/[1-pretest probability])”; “Post-test odds —The odds that a patient has the target disease after being tested (pretest odds×LR)”; “Two mnemonics that capture the properties of such tests have been coined: SnNOut (high sensitivity, negative, rules out) and SpPIn (high specificity, positive, rules in).”; “Studies quoted as showing SpPIn or SnNOut properties may be affected by spectrum bias, partial verification bias, or incorporation bias. Others may be too small to define test characteristics with sufficient precision”; “The power of a test to rule a diagnosis out does not depend exclusively on its sensitivity, as suggested by the SnNOut rule, but is reduced by low specificity. Similarly, the power to rule in depends on both specificity and sensitivity”; “post-test probabilities (with 95% confidence intervals) should be calculated when evaluating potential SnNOut or SpPIn tests”; “Assuming that a diagnosis can be ruled in or out with confidence, when in reality it cannot, could have serious consequences for patients”; “Positive predictive value (PPV) —The proportion of individuals with positive test results who have the target condition. This equals the post-test probability given a positive test result”.
13. Deeks JJ, Altman DG. Diagnostic tests 4: likelihood ratios (BMJ 2004;329(7458):168-169; DOI 10.1136/bmj.329.7458.168; PMID 15258077; PMC478236; full text as shown on PubMed Central). Checked October 30, 2026.
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    “Each test result has its own likelihood ratio, which summarises how many times more (or less) likely patients with the disease are to have that particular result than patients without the disease.”; “A likelihood ratio greater than 1 indicates that the test result is associated with the presence of the disease, whereas a likelihood ratio less than 1 indicates that the test result is associated with the absence of disease.”; “Likelihood ratios above 10 and below 0.1 are considered to provide strong evidence to rule in or rule out diagnoses respectively in most circumstances.”; “The post-test odds that the patient has the disease are estimated by multiplying the pretest odds by the likelihood ratio.”; “Likelihood ratios provide a solution as they can be used to calculate the probability of abnormality, while adapting for varying prior probabilities of the chance of abnormality from different contexts.”.

Medical disclaimer. This page is for general educational purposes and does not constitute medical advice, diagnosis, or treatment. It is a written reference for licensed clinicians and does not replace hands-on training in the examination. Published accuracy figures come from the study populations named beside them and may not match a given patient.