Referral bias in aneurysmal subarachnoid hemorrhage

Abstract

The objective of this study was to assess the effect of referral bias on survival in patients with subarachnoid hemorrhage (SAH). The characteristics of 49 patients with aneurysmal SAH from a single community were compared with those of 328 patients referred from outside the community, all treated in the same medical care setting. In addition, referral patients who received surgery were compared by differential survival analysis with those still awaiting surgery at Days 1 to 3, Days 4 to 10, and Days 11 to 15. There was a dramatic difference in the 30-day survival rate between referral patients (83%) and community patients (59%), but most of the difference had occurred by the 2nd day after SAH. In the referral patients, the variables present at first medical attention that were found to have an independent effect on survival were clinical grade, presence of coma, number of days from SAH to referral, diastolic blood pressure, and patient age. There was a higher survival rate at 1 year for patients who were surgically treated compared with those awaiting surgery for each of the three time periods. Patients who underwent early surgical treatment had a 1-year survival rate almost identical to that of patients with late surgery. Referral patients had a better early survival rate than did community patients because the referral group did not include patients who died and some who were in poor clinical condition before the opportunity for referral. The differential survival analysis described provides a new method for estimating survival for treated and untreated patients with SAH.

Complication Rates Between Local and Referral Patients Undergoing Vaginal Hysterectomy at an Academic Medical Center

“…This is similar to the findings from Whisnant et al, 5 who reported that 2-day survival of referral patients with subarachnoid hemorrhage was markedly better than that of local patients because the referral group did not include those who died quickly or those who were too unstable to be transferred.…”

Ruptured giant intracranial aneurysms. Part I. A study of rebleeding

“…Second, relatively few patients from the subgroup of 63 were admitted to our hospital within 24 hours after their initial hemorrhage, a period representing the peak interval for rebleeding from aneurysms of all sizes. [5,8] For these reasons, to minimize referral bias, [28] the reference point used to calculate the rebleeding rate was the time of admission to our institution (Day 0) rather than the time of the initial hemorrhage. As a result, our findings reflect the expected rate of rebleeding after admission among patients suffering ruptured giant aneurysms who were referred to experienced neurosurgeons at medical centers similar to our own.…”

“…Data from this subgroup were used to calculate the incidence of rebleeding during the first 2 weeks after admission to our hospital, and life table methods were used to estimate cumulative frequency of rebleeding, with patients being excluded if they died of another cause during the first 2 weeks after admission. To minimize inaccuracy caused by referral bias, [28] the time of admission to our institution rather than the time of initial hemorrhage was used as the reference point (Day 0) in estimating the rebleeding rate.…”

The Incidence of Aneurysmal Subarachnoid Hemorrhage in Youngdong District, Korea

“…In community-based studies, if study covers a large geographic region, a number of SAH patients, especially those in the outlying areas, may never reach the hospital and die before receiving medical care or may be treated at hospital of other district 14,24) . On the contrary, if populations are too small, it is difficult to assess accurate incidence rates 14,17,23) .…”