Table 3.
Repeatability of Biomarker Concentrations by Years Stored at −80° C
| Serum | Plasma | ||
|---|---|---|---|
| Storage Time at −80° C | 5 years | 14 years | 16 years |
| Aβ40, pg/ml (N sample pairs) | 10 | 10 | 7 |
| Original, Mean (SD) | 135.9 (42.5) | 150.1 (62.6) | 297.7 (112.1) |
| Replicate, Mean (SD) | 133.7 (51.7) | 164.3 (39.2) | 319.6 (65.5) |
| Difference (replicate – original) | −2.2 | 14.1 | 21.9 |
| p-difference | 1.00 | 1.00 | 1.00 |
| Aβ42, pg/ml (N sample pairs) | 10 | 10 | 7 |
| Original, Mean (SD) | 11.10 (10.8) | 12.0 (4.8) | 14.0 (4.6) |
| Replicate, Mean (SD) | 11.07 (10.3) | 13.2 (3.7) | 15.3 (2.0) |
| Difference (replicate – original) | −0.02 | 1.2 | 1.3 |
| p-difference | 0.75 | 0.11 | 0.45 |
| Aβ42/Aβ40 ratio (N sample pairs) | 10 | 10 | 7 |
| Original, Mean (SD)a | 83.5 (15.4) | 86.8 (30.9) | 49.3 (8.3) |
| Replicate, Mean (SD)a | 83.9 (11.1) | 79.6 (9.9) | 48.7 (6.1) |
| Difference (replicate – original)a | 0.4 | −7.2 | −0.6 |
| p-difference | 0.75 | 0.75 | 1.00 |
| T-Tau, pg/ml (N sample pairs) | 6b | 7b | 7 |
| Original, Mean (SD) | 0.51 (0.30) | 0.58 (0.30) | 1.88 (0.85) |
| Replicate, Mean (SD) | 0.39 (0.20) | 0.49 (0.18) | 1.99 (0.50) |
| Difference (replicate – original) | −0.11 | −0.09 | 0.12 |
| p-difference | 0.69 | 0.45 | 1.00 |
| Serum | |||
| Storage Time at −80⁰ C | 5 years | 14 years | 20 years |
| NfL, pg/ml (N sample pairs) | 9c | 10 | 7 |
| Original, Mean (SD) | 23.7 (13.0) | 13.0 (6.0) | 16.1 (5.3) |
| Replicate, Mean (SD) | 24.5 (12.0) | 13.1 (6.3) | 18.5 (5.8) |
| Difference (replicate – original) | 0.9 | 0.1 | 2.3 |
| p-difference | 0.51 | 1.00 | 0.13 |
Aβ: Amyloid beta; NfL: Neurofilament Light; SD: Standard deviation; T-Tau: Total Tau.
a
Aβ42/Aβ40 ratios multiplied by 1000.
b
Original-Replicate pairs with 1 or both samples below the Limit of Detection (LOD) were not included (5 years: n=4; 14 years: n=3).
c
NfL concentration was not available for n=1 replicate sample.