Table 1.

Summary of the preanalytical variable assessments in this study

Parameter	Factor	Outcome∗
Circadian rhythm (Fig. 1A)	•Time of day of blood collection: 8:00, 12:00, 15:00	•Small diurnal variability observed for Aβ(1-40), Aβ(1-42), tTau; no effect for Aβ(1-42): Aβ(1-40) ratio
Anticoagulant (Fig. 1B) (EDTA used as reference)	•Li-heparin	•Increase of Aβ(1-40) and Aβ(1-42); decrease of tTau
	•Na-citrate	•Decrease of Aβ(1-40), Aβ(1-42), tTau; increase for Aβ(1-42): Aβ(1-40) ratio
Tube parameters (Fig. 1C; Fig. 1D)	•Material: PP, PET	•No effect
	•Sample size (mL): 2.7, 4.9, 8.5, 9, 10	•No effect
	•EDTA cation: K2, K3	•No effect
	•Gel separator: +/-	•No effect
	•Filling height: full, half-filling height	•Decrease of tTau
Whole blood stability in EDTA tube (Fig. 2A)	•Time to centrifugation (h): 0.5, 1, 2, 6, 24	•Aβ(1-40) and Aβ(1-42) stable up to 1h
		•If Aβ(1-42): Aβ(1-40) ratio is reported, stable up to 2h
		•tTau stable up to 6h
EDTA plasma storage after thawing (Fig. 2B)	•+4°C; time to measurement (h): 0, 1, 6, 24	•Aβ(1-40) and Aβ(1-42) stable up to 6h at +4°C and 1h at RT
	•RT; time to measurement (h): 0, 1, 6, 24	•Aβ(1-42): Aβ(1-40) ratio stable up to 24h† (both +4°C and RT)
Fresh EDTA plasma storage (Fig. 2C)	•+4°C; time to measurement (h): 0, 1, 3, 6, 24	•Stable up to 6h
Number of tube transfers (Fig. 3A)	•1×, 2×, 3×, 4×, 5×	•No effect
Effect of the collection tube on stability during freezing (Fig. 3B)	•Material (PP, PET)	•No effect
	•Sample size (mL): 2.7, 4.9, 8.5, 9, 10	•No effect
	•EDTA cation (K2, K3)	•No effect
	•Gel separator (+/-)	•No effect
Freeze/thaw cycles (–80°C) (Fig. 3C)	•1×, 2×, 3×	•No effect
Freeze/thaw cycles (–25°C) (Fig. 3D)	•1×, 2×, 3×	•No effect
Freeze/thaw cycles (–20°C) (Fig. 3D)	•1×, 2×, 3×	•No effect

Abbreviations: Aβ, amyloid β; EDTA, ethylenediaminetetraacetic acid; Li-heparin, lithium heparin; PET, polyethylene terephthalate; PP, polypropylene; RT, room temperature; tTau, total Tau.

^∗Outcomes listed apply to all peptide measures unless otherwise indicated.

^†Only Aβ(1-40) and Aβ(1-42) and Aβ(1-42): Aβ(1-40) assessed; tTau not evaluated due to the high stability of tTau in thawed plasma.