Diagnostic evidence: how good is the test?

Ask whether a test or a rule changes the diagnosis. Vero answers with the sensitivity, specificity, and likelihood ratios the studies measured, each one linked.

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Sensitivity and specificity
Likelihood ratios
Pre-test and post-test probability
Decision rules
Imaging choices
Lab tests

Put a test to the question. Pick one.

D-dimer for PE

Ruling out PE at low pretest probability

The hematology guideline, and a prospective study of 2,017 outpatients.

Low pretest probability of PE. D-dimer or CT first?

Sensitivity97%Specificity39%LR−0.08ashpublications

D-dimer first. If it is negative, PE is excluded without imaging. ashpublications

Of 1,325 outpatients ruled out by pretest probability and D-dimer, none had VTE at 3 months. pubmedL2

American Society of Hematology 2018 guidelines for management of venous thromboembolism: diagnosis of venous thromboembolismClinical guideline · ASH 2018ashpublications
Diagnosis of pulmonary embolism with d-dimer adjusted to clinical probabilityProspective cohort · 2,017 patientspubmedL2

Minor head injury, GCS 15. Which rule decides on CT?

Sensitivity100%Specificity76.3%New Orleans specificity12.1%pubmedL2

The Canadian CT Head Rule. It and the New Orleans Criteria both caught every patient who needed neurosurgery. pubmedL2

The Canadian rule was far more specific: CT for 52% of patients, against 88% with New Orleans. pubmedL2

It was derived in 3,121 adults at ten Canadian hospitals. pubmedL2

The Canadian CT Head Rule for patients with minor head injuryProspective cohort · 3,121 patientspubmedL2
Comparison of the Canadian CT Head Rule and the New Orleans Criteria in patients with minor head injuryProspective cohort · 2,707 patientspubmedL2

Thunderclap headache, CT normal at 4 hours. Still need an LP?

Sensitivity98.7%Specificity99.9%LR−0.010pubmedL1

Usually not, if the patient is neurologically intact and a modern CT, read by a radiologist, was done within 6 hours of onset. pubmedL2 pubmedL1

Within 6 hours, CT found all 121 hemorrhages among 953 patients. pubmedL2

Sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage: prospective cohort studyProspective cohort · 3,132 patientspubmedL2
Sensitivity of early brain computed tomography to exclude aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysisMeta-analysis · 8,907 patientspubmedL1

How accurate is a single FIT for colorectal cancer?

Sensitivity79%Specificity94%LR+13.1pubmedL1

It finds about 4 in 5 cancers, at 94% specificity. A cutoff under 20 µg/g raises sensitivity to 89%, with lower specificity. pubmedL1

Screen all adults 45 to 75; FIT is one of the options. uspreventiveservicestaskforce

Accuracy of fecal immunochemical tests for colorectal cancer: systematic review and meta-analysisMeta-analysis · 19 studiespubmedL1
Screening for colorectal cancer: US Preventive Services Task Force recommendation statementRecommendation · USPSTF 2021uspreventiveservicestaskforce

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Pre-test to post-test, worked once with real numbers.

Ask Vero to show the working. Odds in, likelihood ratio applied, probability out.

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Child with a sore throat. What does a rapid strep test change?

Pre-test probabilityChildren with a sore throat37%pubmedL1
SensitivityRapid antigen test vs culture85.6%pubmedL1
Specificity95.4%pubmedL1

Likelihood ratiosLR+ 0.856 ÷ 0.046 · LR− 0.144 ÷ 0.95418.6 · 0.15
Pre-test odds0.37 ÷ 0.630.59
Test positive0.59 × 18.6 = 10.9 odds92%
Test negative0.59 × 0.15 = 0.089 odds8%

Probability of strep

8%Test negative37%Before the test92%Test positive

0%100%

Positive: treat, no culture needed. Negative: still about 8%, so back it up with a throat culture in children. idsociety

Decision rules, and what each one rules out.

Six rules Vero cites, with the studies behind them. Several were built in Canadian emergency departments.

Ottawa ankle rules

Adults with an acute ankle injury. Stiell, JAMA 1993.

Canadian CT Head Rule

Minor head injury, GCS 13 to 15. Stiell, Lancet 2001.

Canadian C-Spine Rule

Alert, stable trauma patients. Stiell, JAMA 2001.

Ottawa SAH Rule

Alert adults with a headache that peaked within an hour. Perry, JAMA 2013.

Wells score for PE

Suspected pulmonary embolism. Wells, Thromb Haemost 2000.

PERC rule

Only when pretest probability is already low. Kline, J Thromb Haemost 2004.

Evidence at the point of the decision.

Ask mid-visit, with the patient attached

Vero reads the chart, so a rule is applied to the patient in front of you.

Upload the report

Attach a lab result or an imaging report, up to 50 MB, and ask what it changes.

Your department’s pathways

Add them to a library the team shares. Answers name the pathway they used.

Clear about thin evidence

When studies are small or disagree, the answer says so, with the sources.

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Ask the way you would ask a colleague in the corridor.

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Questions about diagnostic evidence.

What is diagnostic evidence?

Studies of how well a test, a sign, or a decision rule finds or excludes a condition, and the guidelines built on them. Vero cites them in one answer.

What do sensitivity and specificity mean?

Sensitivity is the share of people with the condition who test positive. Specificity is the share of people without it who test negative.

What is a likelihood ratio?

How far a result shifts the odds of disease. Ratios above 10 or below 0.1 shift them a lot; ratios near 1 barely move them.

How do I get from pre-test to post-test probability?

Turn the probability into odds, multiply by the likelihood ratio, and turn the odds back into a probability. Ask Vero to show each step.

Which clinical decision rules can Vero cite?

Published rules such as the Ottawa ankle and knee rules, the Canadian CT Head and C-Spine rules, the Ottawa SAH Rule, Wells, and PERC, with the studies that derived and validated them.

Can I attach a lab result or an imaging report?

Yes. Upload files up to 50 MB each, such as lab results or imaging reports, and ask about them. Images are read as extracted text.

Can I check a decision rule mid-visit?

Yes. Vero Scribe keeps recording while you type, and the cited reply comes back in the chat.

Is there a free plan?

Yes. Vero Evidence is part of every plan, including Free, with 10 actions a month and no credit card. Pro is unlimited.

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From the diagnosis to the rest of Vero Evidence.

Treatment evidence

The options for a condition, and the evidence for each.

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PICO questions

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Clinical guideline search

The current recommendation, from the body that issued it.

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Contextual evidence

Answers that account for the patient in front of you.

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Know what the result means before you order the next test.

Accuracy figures and decision rules, cited from the studies that measured them.

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