Fifty patients were enrolled. Age, race, gender, and mechanism of injury are described in , stratified by whether or not serum C-tau was detected. There were 15 patients with detectable levels of C-tau (30.0%, 95CI 18.3% to 44.8%). Of these 15 patients, the mean serum C-tau concentration was 5.02 ng/ml (SD 2.98 ng/ml). The time from injury to measurement of C-tau was similar between groups ().
Characteristics of patients in the study, stratified by whether or not serum C-tau was detected. Data are frequencies and percents or means and standard deviations as appropriate.
Fourteen percent of patients with a GCS of 15 and 35.7% of patients with a GCS of 13 or 14 had at least one traumatic abnormality on head CT (described in ). Abnormal findings on CT were similarly likely among those with and without C-tau. The sensitivity and specificity for intracranial abnormality on head CT were 50.0% (95CI 20.1–79.9%) and 75.0% (95CI 58.5–86.8%), respectively.
Prevalence of CT-demonstrated intracranial abnormalities
The mean time to follow-up was 20 weeks (SD 6 weeks). There was no difference in time to follow-up between those with and those without a measurable C-tau level (p=0.223). Due to cognitive impairments, one patient had his wife answer questions on his behalf. Two patients could not be contacted by telephone and completed the questionnaires after they were mailed to them. Nine patients were lost to follow-up. Of the subjects who underwent follow-up, the proportion with PCS was similar between those with and without C-tau detected. The sensitivity and specificity for PCS were 22.7% (95CI 8.7 – 45.8%) and 52.6% (95CI 29.5 – 74.8%), respectively. Even though only the presence or absence of C-tau in serum was used to address our study hypothesis, we decided to determine if there might be an underlying association between absolute serum C-tau levels, timing of blood draw, and outcome. There does not appear to an association between serum C-tau levels, timing of blood draw, head CT results, and PCS ().
Figure 1 Plots demonstrating serum C-tau levels versus blood draw time stratified by the presence or absence of 3-month PCS in all patients (A). Patients were further subdivided by head CT results (B and C). One patient with a serum C-tau level of 3.41 ng/ml was (more ...)
Among all patients, the RPQ score was lower (fewer or less severe symptoms) among those with measurable C-tau than among those without measurable C-tau. The SF-36 mental component summary score was higher, which represents better functioning, among those with detectable C-tau than among those without detectable C-tau. The two groups did not differ on the SF-36 physical component summary score or cognitive component summary score.
Subgroup analysis of all patients with a negative initial head CT scan was performed. Among the 31 patients with a negative head CT scan and who were followed up, C-tau was detected in 9. Four out of the nine (44.4%) with detectable C-tau had PCS, while 15/22 (68.2%) without detectable C-tau had PCS (p=0.253). In this subgroup, the sensitivity and specificity for PCS were 21.1% (95CI 7.0 – 46.1%) and 58.3% (95CI 28.6 – 83.5%), respectively. Those with detectable C-tau scored better on the RPQ (5.7 v 16.4, p=0.011) and the SF-36 mental component (57.6 v 44.5, p=0.005), than those who did not. Subjects with detectable C-tau did not differ from those without detectable C-tau on the SF-36 physical component summary score (46.3 v 48.8, p=0.379) or cognitive component summary score (72.7 v 62.9, p=0.182).