Figure 1Differences of proGRP concentrations between paired plasma and serum samples (ΔproGRP). proGRP = progastrin-releasing peptide; ΔproGRP = plasma progastrin-releasing peptide concentration–serum progastrin-releasing peptide concentration.
Figure 2Accuracy of ΔproGRP in discriminating plasma and serum samples that had been exposed to four freeze–thaw cycles, compared with those subjected to one freeze–thaw cycle. ΔproGRP = plasma progastrin-releasing peptide concentration–serum progastrin-releasing peptide concentration.
Table 1Changes of proGRP levels in plasma and serum samples exposed to repeated freeze–thaw cycles.
Sample type |
No. of freeze–thaw cycles |
proGRP concentrations (pg/mL)
|
Range |
Mean (±SD) |
Change (%)∗
|
p†
|
Plasma |
1 |
27.6–91.6 |
41.3 (±14.9) |
|
— |
2 |
28.4–84.8 |
40.1 (±13.6) |
−2.9 |
0.006 |
3 |
28.6–85.6 |
40.5 (±13.9) |
−1.9 |
0.014 |
4 |
26.2–87.8 |
40.0 (±14.1) |
−3.1 |
0.003 |
Serum |
1 |
24.3–83.4 |
36.5 (±13.6) |
|
— |
2 |
21.9–79.9 |
34.9 (±13.6) |
−4.4 |
<0.001 |
3 |
19.5–77.2 |
34.0 (±13.1) |
−6.8 |
<0.001 |
4 |
18.2–77.9 |
32.8 (±13.5) |
−10.1 |
<0.001 |
Table 2Thawing time at 37°C and exposure time at room temperature during repeated freezing and thawing of plasma and serum samples.
Sample processing time (min) |
Sample type |
No. of freeze–thaw cycles
|
1 |
2 |
3 |
4 |
Thawing time at 37°C |
Plasma |
2.2 |
4.2 |
6.5 |
8.5 |
(0.4) |
(0.4) |
(0.8) |
(0.8) |
Serum |
2.3 |
4.3 |
6.7 |
8.7 |
(0.8) |
(0.8) |
(1.0) |
(1.0) |
Exposure time at room temperature |
Plasma |
1.3 |
1.9 |
2.4 |
3.2 |
(0.2) |
(0.6) |
(0.8) |
(0.9) |
Serum |
1.1 |
1.9 |
2.2 |
2.9 |
(0.1) |
(0.4) |
(0.7) |
(1.0) |