Table 2.

Rate ratios (RR) and 95% confidence intervals (CI) of ischemic stroke according to quintiles of protein C, ARIC, 1987–2005

	Protein C Percentiles
	<20^th	20^th–39^th	40^th–59^th	60^th–79^th	≥80^th	P for trend
Range, μg/mL	<2.6	2.7–2.9	3.0–3.2	3.3–3.6	≥3.7
No. at risk	2,705	2,650	2,899	2,871	2,754
No. of cases	142	109	124	123	115
Person-years of follow-up	41,829	41,897	46,014	45,524	43,955
Incidence rate/1000 person-years	3.4	2.6	2.7	2.7	2.6
Age-, race-, and sex-adjusted RR (95% CI)	1.26 (0.98–1.61)	0.99 (0.76–1.29)	1.04 (0.80–1.34)	1.02 (0.79–1.31)	1.0	0.13
Multivariate-adjusted^* RR (95% CI)	1.38 (1.07–1.77)	1.08 (0.83–1.41)	1.13 (0.88–1.47)	1.11 (0.86–1.44)	1.0	0.03
Multivariate-adjusted^† RR (95% CI)	1.52 (1.17–1.98)	1.18 (0.90–1.55)	1.22 (0.94–1.58)	1.16 (0.90–1.50)	1.0	0.004

Adjusted for age, race-field center, sex, systolic blood pressure, use of antihypertensive medication, smoking status, diabetes mellitus, and education.

^†

Further adjustment for LDL cholesterol, HDL cholesterol, fibrinogen, and von Willebrand factor.