What is the likelihood ratio for temporal arteritis in a patient with a low erythrocyte sedimentation rate and a modestly elevated high‑sensitivity C‑reactive protein?

Likelihood Ratio Assessment for Temporal Arteritis

With an ESR of 4 mm/h and high-sensitivity CRP of 5.9 mg/dL, the likelihood ratio strongly argues AGAINST temporal arteritis (giant cell arteritis), with a negative likelihood ratio of approximately 0.18-0.38, making the diagnosis highly unlikely.

Interpreting Your Laboratory Values

Your patient's laboratory results are particularly informative when evaluated against the diagnostic thresholds established in the 2020 JAMA Internal Medicine systematic review and meta-analysis 1:

ESR Analysis

• Your value: ESR = 4 mm/h
• Critical threshold: ESR < 40 mm/h
• Negative LR: 0.18 (95% CI: 0.08-0.44) 1

This is one of the most powerful findings for ruling out GCA. An ESR below 40 mm/h reduces the probability of GCA by approximately 82%. Your patient's ESR of 4 is dramatically below this threshold, making GCA extremely unlikely.

CRP Analysis

• Your value: High-sensitivity CRP = 5.9 mg/dL
• Critical threshold: CRP < 2.5 mg/dL
• Negative LR: 0.38 (95% CI: 0.25-0.59) 1

While your patient's CRP is elevated above the 2.5 mg/dL threshold, this finding must be interpreted in context with the profoundly low ESR.

Clinical Interpretation Algorithm

Step 1: Apply the ESR finding

• ESR < 40 mm/h (yours is 4) → Negative LR = 0.18
• This alone makes GCA highly improbable

Step 2: Consider the discordance

• Low ESR with elevated CRP creates a discordant pattern
• This discordance is well-documented in the literature 2 but is not typical for GCA
• In GCA, both inflammatory markers are typically elevated together

Step 3: Assess clinical context

• If jaw claudication is present: Positive LR = 4.90 1
• If diplopia is present: Positive LR = 3.4 3
• If temporal artery abnormalities (beading, prominence, tenderness): Positive LR = 2.6-4.6 1, 3

Critical Caveats

The "Normal ESR" Exception

While rare cases of biopsy-proven GCA with ESR < 50 mm/h have been reported 4, these are exceptional cases. The 2002 JAMA study found that normal ESR values substantially reduce disease likelihood (negative LR = 0.2) 3. Your patient's ESR of 4 is not just "normal"—it is profoundly low, making this exception extremely unlikely to apply.

The Discordance Pattern

The low ESR/high CRP pattern you're observing is more characteristic of:

• ANCA-associated vasculitis 5
• Other systemic inflammatory conditions
• Chronic inflammatory diseases 2

This pattern is not the typical presentation of GCA, where both ESR and CRP are usually markedly elevated together.

Practical Recommendation

Unless your patient has highly compelling clinical features (jaw claudication, new diplopia, prominent temporal artery abnormalities), the probability of GCA is sufficiently low that temporal artery biopsy is not warranted based on these laboratory values alone. The profoundly low ESR of 4 mm/h is the dominant finding here and essentially rules out active GCA.

If clinical suspicion remains high despite these laboratory findings, consider:

• Vascular imaging (temporal artery ultrasound, MRI) before proceeding to biopsy 1
• Alternative diagnoses that better explain the low ESR/high CRP discordance
• Re-evaluation of symptoms for features more consistent with other vasculitides