Table 2.
Comparison of GFAP concentrations in serum and plasma in the total sample and head CT subgroups.
| Total sample | No head CT | Normal head CT | Abnormal head CT | |||||
|---|---|---|---|---|---|---|---|---|
| (N = 121) | (n = 29) | (n = 70) | (n = 22) | |||||
| Plasma | Serum | Plasma | Serum | Plasma | Serum | Plasma | Serum | |
| Descriptive statistics (pg/mL) | ||||||||
| Mean | 635.9 | 497.0 | 400.3 | 401.4 | 459.1 | 344.5 | 1509.2 | 1108.2 |
| Median | 326.8 | 272.1 | 207.3 | 217.1 | 315.9 | 263.0 | 928.6 | 787.8 |
| Standard deviation | 972.6 | 700.5 | 790.1 | 867.2 | 535.7 | 412.4 | 1627.8 | 872.3 |
| Interquartile range | 189.9–595.1 | 157.2–503.3 | 137.1–337.0 | 122.3–302.1 | 176.3–564.9 | 147.8–433.5 | 411.0–2035.6 | 353.5–2096.6 |
| Range | 52.2–6838.6 | 32.6–4813.8 | 52.2–4420.0 | 32.6–4813.8 | 63.4–4027.7 | 48.7–3382.4 | 139.6–6838.6 | 114.4–2640.7 |
| Difference score (plasma – serum) | ||||||||
| Mean | 138.9 | −1.1 | 114.6 | 401.0 | ||||
| Median | 28.0 | 0.65 | 37.7 | 230.1 | ||||
| Standard deviation | 509.2 | 90.7 | 237.9 | 1088.0 | ||||
| Interquartile range | −15.5 to 140.4 | −21.6 to 39.6 | −9.0 to 144.4 | −54.7 to 612.0 | ||||
| Range | −1612.0 to 4197.8 | −393.8 to 129.4 | −118.6 to 1328.7 | −1612.0 to 4197.83 | ||||
| Percentage with plasma > serum | 64.5% | 55.2% | 68.6% | 63.6% | ||||
| Group comparisons | ||||||||
| Wilcoxson signed ranks test (z) | 4.62 (p < 0.001) | 0.75 (p = 0.456) | 4.46 (p < 0.001) | 2.09 (p = 0.036) | ||||
| Effect sizes (r) | 0.42 | 0.14 | 0.53 | 0.45 | ||||
| Effect sizes (Cohen's d) | 0.16 | 0.001 | 0.24 | 0.31 | ||||
| Spearman correlations | ||||||||
| Age and GFAP level | 0.495** | 0.540** | 0.489** | 0.540** | 0.508** | 0.631** | −0.028 | −0.061 |
| Time to blood sampling | 0.243** | 0.206* | 0.315 | 0.308 | 0.158 | 0.074 | 0.455* | 0.387 |
| Values from two assays | 0.886** | 0.907** | 0.862** | 0.826** | ||||
*
p < 0.05 and
**
p < 0.01; CT, computed tomography; GFAP, glial fibrillary acidic protein.