Consent for long-term storage of blood samples by Indigenous Australian research participants: the DRUID Study experience

Table 3 Relationship of consent to store blood samples with selected biochemical measurements. Among 854 urban Indigenous Australian research participants who completed a questionnaire and provided a fasting blood sample in 2003–2005.

		Did not agree to long-term storage (n = 356)		Agreed to long-term storage (n = 498)
	n	Geometric mean	95% CI	Geometric mean	95% CI
Fasting glucose (mmol/L)
All participants	854	5.5	5.3, 5.6	5.6	5.5, 5.7
Participants with diabetes†	149	8.7	7.8, 9.7	8.4	7.8, 9.0
Participants without diabetes†‡	548	5.0	4.9, 5.0	5.0	4.9, 5.0
Fasting insulin (mU/L)
All participants	853	9.4	8.7, 10.2	9.8	9.1, 10.4
Participants with diabetes†	148	13.8	11.0, 17.3	15.0	12.8, 17.6
Participants without diabetes†‡	548	8.3	7.6, 9.1	8.0	7.5, 8.7
Total cholesterol (mmol/L)	849	4.9	4.8, 5.1	4.9	4.8, 5.0
HDL cholesterol (mmol/L)	849	1.1	1.1, 1.1	1.1	1.1, 1.2
LDL cholesterol (mmol/L)	813	3.0	2.9, 3.1	2.9	2.8, 3.0
Triglycerides (mmol/L)	849	1.5	1.4, 1.6	1.5	1.4, 1.5
Homocysteine (umol/L)	854	9.5	9.1, 9.9	9.4	9.1, 9.7
Fibrinogen (g/L)	829	3.7	3.5, 3.8	3.6	3.5, 3.8
Haemoglobin A1c (%)	843	5.5	5.4, 5.6	5.6	5.5, 5.7
C-reactive protein (mg/L)	848	3.2	2.8, 3.7	3.0	2.7, 3.4

	Estimated percent difference in the mean associated with consent to store blood sample*
	Crude		Adjusted for age and sex
	% difference	95% CI	% difference	95% CI
Fasting glucose (mmol/L)
All participants	2.2	-1.4, 5.9	0.6	-2.8, 4.0
Participants with diabetes†	-4.0	-15.0, 8.3	-1.3	-12.8, 11.6
Participants without diabetes†‡	0.2	-1.3, 1.7	0.1	-1.4, 1.5
Fasting insulin (mU/L)
All participants	3.6	-6.7, 14.9	1.7	-8.3, 12.8
Participants with diabetes†	9.1	-16.6, 42.7	8.7	-17.3, 42.8
Participants without diabetes†‡	-3.5	-14.2, 8.4	-4.0	-14.4, 7.8
Total cholesterol (mmol/L)	-1.7	-4.4, 1.2	-2.1	-4.7, 0.6
HDL cholesterol (mmol/L)	2.5	-1.4, 6.6	3.1	-0.7, 7.1
LDL cholesterol (mmol/L)	-2.1	-6.0, 2.1	-2.4	-6.3, 1.6
Triglycerides (mmol/L)	-3.6	-10.9, 4.3	-6.4	-12.9, 0.5
Homocysteine (umol/L)	-1.0	-5.8, 4.1	-2.7	-7.2, 2.0
Fibrinogen (g/L)	-0.1	-4.8, 4.8	-0.9	-5.5, 4.0
Haemoglobin A1c (%)	0.7	-1.9, 3.3	-0.7	-3.0, 1.6
C-reactive protein (mg/L)	-6.4	-21.3, 11.3	-9.7	-23.1, 6.1

* Calculated as 100(e^β -1), using the relevant regression coefficient from a linear regression model with the dependent variable measured on the log scale.
† Participants were classified as having diabetes if they met any of the following criteria: 1) fasting plasma glucose ≥ 7.0 mmol/L; 2) 2-hour post-glucose load plasma glucose ≥ 11.1 mmol/L; or 3) previously diagnosed as having diabetes and currently taking tablets and/or insulin for diabetes. Among participants who were not currently taking tablets and/or insulin for diabetes, impaired glucose tolerance (IGT) was considered present if fasting glucose was < 7.0 mmol/L and 2-hour glucose was ≥ 7.8 and < 11.1 mmol/L; impaired fasting glucose (IFG) was considered present if fasting glucose was ≥ 6.1 and < 7.0 mmol/L, and 2-hour glucose was less than 7.8 mmol/L.
‡ Excludes those with impaired fasting glucose or impaired glucose tolerance, or whose diabetic status could not be classified.