Investigations

• ESR or plasma viscosity ^c

Note:

• A normal ESR or plasma viscosity does not rule out giant cell arteritis. ^{a c}

An elevated ESR or plasma viscosity helps diagnose giant cell arteritis

Patient c	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
suspected giant cell arteritis (pre-test probability: 48%)	giant cell arteritis (positive temporal artery biopsy)	ESR ≥ 60 mm/hr	6.9 (1.9 to 26)	87%	0.16 (0.041 to 0.56)	13%
		plasma viscosity ≥1.8 units	5.3 (1.3 to 13)	81%	0.16 (0.044 to 0.61)	13%

• Around 20% of patients with GCA have a normal ESR when first seen. ^a