Temporal Arteritis

Diagnostics and Likelihood Ratios, Explained

Positive Findings (Patient Has This)

Finding (Sign/Symptom/Lab/Study)Number Needed to Diagnose
(Positive Likelihood Ratio)
Beaded temporal artery 4.6×
Prominent or enlarged temporal artery 4.3×
Jaw claudication 4.2×
Diplopia 3.4×
Absent temporal artery pulse 2.7×
Tender temporal artery 2.6×
Any temporal artery abnormality 2.0×
ESR > 100 mm/h 1.9×
Scalp tenderness 1.6×
Optic atrophy or ischemic optic neuropathy 1.6×
Anemia 1.5×
Temporal headache 1.5×
Weight loss 1.3×
Any headache 1.2×
ESR > 50 mm/h 1.2×
Fatigue 1.2×
Fever 1.2×
Anorexia 1.2×
ESR abnormal 1.1×
White Race 1.1×
Any visual symptom 1.1×
Arthralgia 1.1×
Any funduscopic abnormality 1.1×
Polymyalgia rheumatica 0.97×
Myalgia 0.93×
Unilateral visual loss 0.85×
Male se× 0.83×
Vertigo 0.71×
Synovitis 0.41×

Negative Findings (Patient Doesn't Have This)

Finding (Sign/Symptom/Lab/Study)Number Needed to Diagnose
(Negative Likelihood Ratio)
ESR abnormal 0.2×
ESR > 50 mm/h 0.35×
Any temporal artery abnormality 0.53×
Prominent or enlarged temporal artery 0.67×
Any headache 0.7×
Absent temporal artery pulse 0.71×
Jaw claudication 0.72×
Anemia 0.79×
Optic atrophy or ischemic optic neuropathy 0.8×
ESR > 100 mm/h 0.8×
Temporal headache 0.82×
Tender temporal artery 0.82×
Anorexia 0.87×
Weight loss 0.89×
Fever 0.92×
Scalp tenderness 0.93×
Beaded temporal artery 0.93×
Fatigue 0.94×
Diplopia 0.95×
Any visual symptom 0.97×
Polymyalgia rheumatica 0.99×
Arthralgia 1.0×
Any funduscopic abnormality 1.0×
Myalgia 1.1×
Vertigo 1.1×
Synovitis 1.1×
Unilateral visual loss 1.2×


  • Data derived from a highly selected (referral) population.
  • Prevalence: 39% overall in 21 studies (prevalence of TA in general Population:1%)
  • Outcome: Positive temporal artery biopsy
  • The authors' analysis suggests that there are only a few signs, symptoms, or tests that have significant predictive value for this preselected population.
  • The rest of the signs, symptoms or tests have little or no predictive value for this preselected population.


It is unclear how these LR's are generalizable to the population at large.


Rodrigo Kong, MD


February 22, 2012

What are Likelihood Ratios?

LR, pretest probability and posttest (or posterior) probability are daunting terms that describe simple concepts that we all intuitively understand.

Let's start with pretest probability: that's just a fancy term for my initial impression, before we perform whatever test it is that we're going to use.

For example, a patient with prior stents comes in sweating and clutching his chest in agony, I have a pretty high suspicion that he's having an MI – let's say, 60%. That is my pretest probability.

He immediately gets an ECG (known here as the "test") showing an obvious STEMI.

Now, I know there are some STEMI mimics, so I'm not quite 100%, but based on my experience I'm 99.5% sure that he's having an MI right now. This is my posttest probability - the new impression I have that the patient has the disease after we did our test.

And likelihood ration? That's just the name for the statistical tool that converted the pretest probability to the posttest probability - it's just a mathematical description of the strength of that test.

Using an online calculator, that means the LR+ that got me from 60% to 99.5% is 145, which is about as high an LR you can get (and the actual LR for an emergency physician who thinks an ECG shows an obvious STEMI).

(Thank you to Seth Trueger, MD for this explanation!)