Example: Lost to Follow-up - HCV and HIV
Lead Author(s): Jeff Martin, MD
Many times lost to follow-up data is not presented.
First Example from a Study with HIV/HCV Co-infected Individuals - Greub
Greub's 2000 Study:
- 3111 patients, 1996 - 1999
- HCV+ more rapid disease progression
- Adj RH = 1.7 (95% CI = 1.3 - 2.3)
- No loss to follow-up info: "Of 3655 individuals starting potent antiretroviral therapy 3111 (85.1%) were eligible for analysis."
Second Example from a Study with HIV/HCV Co-infected Individuals - Sulkowski
Sulkowski's 2002 Study:
- 1955 patients, 1995 - 2001
- HCV not associated with disease progression
- Adj RH = 1.0 (95% CI = 0.9 - 1.2)
- No loss to follow-up info: "Of the 2337 cohort participants enrolled between January 1995 and January 2001, 1995 patients who had at least 1 return visit and who had not developed an AIDS-defining illness prior to enrollment were eligible for analysis."
Analysis of Studies
These are two studies in prestigious journals, who were allowed to publish their results without any data on loss to follow-up or its potential effect on their results. Something they would not have been allowed to do if these were experimental cohorts (i.e., clinical trials).
They are both treatment clinic-based cohorts, which means they counted a patient as in the cohort after two visits to the clinic (a little like a run-in design in a clinical trial where you test whether someone is going to be compliant before enrolling him or her). It also means that their follow-up was driven by return visits to the clinic.
Since they got contrary results with almost identical methodology, one would like to know whether differing follow-up biases had anything to do with the differing results. There is no way to tell from what they published.
References
Greub, G., Ledergerber, B., Battegay, M., Grob, P., Perrin, L., Furrer, H., et al. (2000). Clinical progression, survival, and immune recovery during antiretroviral therapy in patients with HIV-1 and hepatitis C virus coinfection: the Swiss HIV Cohort Study. Lancet, 356(9244), 1800-1805.
Sulkowski, M. S., Moore, R. D., Mehta, S. H., Chaisson, R. E., & Thomas, D. L. (2002). Hepatitis C and progression of HIV disease. Jama, 288(2), 199-206.