Table 2.
Variability in Duplicate Measurements by Years Stored at −80° C
| Serum | Serum | Plasma | |
|---|---|---|---|
| Storage time (years) | 5 | 14 | 16 |
| Dates Collected | 2015-2017 | 2005-2008 | 2003-2005 |
| Aβ40, pg/ml (N samples) | 24 | 24 | 73 |
| Difference in duplicates, Mean (SD) | 1.31 (5.3) | 4.24 (12.6) | 7.64 (15.4) |
| p difference | 0.54 | 0.02 | <0.01 |
| Average CV | 2% | 4% | 3% |
| Aβ42, pg/ml (N samples) | 24 | 24 | 73 |
| Difference in duplicates, Mean (SD) | 0.14 (0.6) | 0.23 (0.6) | 0.20 (0.9) |
| p difference | 0.54 | 0.06 | 0.03 |
| Average CV | 4% | 3% | 4% |
| Aβ42/Aβ40 ratio (N sample pairs) | 24 | 24 | 73 |
| Difference in duplicates, Mean (SD)a | 0.33 (4.9) | −1.92 (6.3) | −0.57 (2.4) |
| p difference | 0.54 | 0.54 | 0.24 |
| T-Tau, pg/ml (N samples) | 15b | 16b | 73 |
| Difference in duplicates, Mean (SD) | 0.01 (0.11) | 0.03 (0.16) | 0.03 (0.23) |
| p difference | 1.00 | 0.21 | 0.35 |
| Average CV | 13% | 17% | 7% |
| Serum | Serum | Serum | |
| Storage time (years) | 5 | 14 | 20 |
| Dates Collected | 2015-2017 | 2005-2008 | 1998-2000 |
| NfL, pg/ml (N samples) | 24 | 24 | 77 |
| Difference in duplicates, Mean (SD) | −0.08 (1.7) | −0.52 (1.0) | −0.08 (0.8) |
| p difference | 0.31 | 0.06 | 0.36 |
| Average CV | 6% | 4% | 4% |
Aβ: Amyloid beta; CV: Coefficient of Variation; NfL: Neurofilament Light; SD: Standard deviation; TTau: Total Tau.
a
Aβ42/Aβ40 ratios multiplied by 1000.
b
Serum Tau samples below Limit of Detection not included (n=9 stored for 5 years and n=8 stored for 14 years).