Screening for human T cell leukaemia/lymphoma virus among blood donors in Sweden: cost effectiveness analysis

British Medical Journal, May 9, 1998 by Elsa Tynell, Soren Andersson, Eva Lithander, Malin Arneborn, Jonas Blomberg, Hans Bertil Hansson, Aud Krook, Mats Nomberg, Kristina Ramstedt, Agneta Shanwell, Anders Bjorkman

Introduction

Human T cell leukaemia/lymphoma viruses types I and II were identified in the early 1980s[1 2]; serological tests for these retroviruses became available in 1986.[3] Infection with the virus is associated with tropical spastic paraparesis,[4] adult T cell leukaemia/lymphoma, and some inflammatory disorders.[5 6] The virus is primarily sexually transmitted,[7] but it may also be transmitted from mother to child either perinatally[7] or through breast feeding.[8 9] The virus may also be transmitted through blood transfusions.[10]

Japan began screening blood donors for infection with the virus in 1986.[11] Similar screening was introduced in the United States in 1988 and in France in 1991. Screening also occurs in Canada, Holland, Australia, Finland, Denmark, Portugal, Greece, and Luxemburg.

In Sweden, after a pilot screening of blood donors in 1993 the National Board for Health and Welfare decided to test all blood donations for one year starting in March 1994. We present an analysis of the cost effectiveness of this screening programme.

Subjects and methods

Blood donation--National data on blood donors and donation practices were obtained from the Swedish Society for Transfusion Medicine and the National Board for Health and Welfare. Before registering for their first blood donation potential donors complete a written questionnaire and are interviewed to assess possible risk factors for infectious diseases. All blood donations are tested for HIV, and hepatitis B and C; only the first donation is tested for syphilis.

Recipients of transfusions--There are no detailed national data on the recipients of blood transfusions. A pilot study was done at the blood bank at South Hospital which serves several other hospitals in the region. Data on 255 randomly selected patients who had received blood components during February 1992 were collected; this data included the age of the patient, survival time after transfusion, and which blood components were received.

National screening programmed--In March 1994, a national one year programme to screen every blood and plasma donation for the human T cell leukaemia/lymphoma virus was launched. Screening tests were performed at blood banks, local microbiological laboratories, or regional virological laboratories. Commercially available enzyme linked immunosorbent assays were used. The assays were performed according to the manufacturers instructions. Positive tests were confirmed by western blotting, according to guidelines issued by the World Health Organisation and the HTLV European Research Network.[12 13] Western blotting was performed in regional virological laboratories or at the Swedish Institute for Infectious Disease Control. All laboratories used Diagnostic Biotechnology HTLV-blot 2.3 (Diagnostic Biotechnology, Science Park, Singapore) for confirmation. For a test to be classed as positive by western blotting, two envelope bands and at least one core band had to be positive. Any other reactivity was classified as indeterminate. All except one of the samples that tested positive by western blotting and several of those classed as indeterminate were also tested by polymerase chain reaction at the Swedish Institute for Infectious Disease Control.[14] Blood from donors with two samples that tested positive by enzyme linked immunosorbent assay was not used even when the tests were not confirmed by western blotting. Donors whose samples were confirmed as positive were informed at the blood bank and referred to a specialist in infectious diseases. The total number of screening tests performed and the number of those with positive results were reported to the Swedish Institute for Infectious Disease Control.

Retrospective study--A decision to trace patients who had received blood components from donors confirmed to be infected with the virus was taken by the National Board for Health and Welfare in 1994. Patients who had received such transfusions were contacted and offered testing. This retrospective study was possible because the blood banks keep records not only of all donors and recipients of blood components but also because we had access to the national census file on all living and recently deceased Swedish citizens.

Cost effectiveness analysis--Cost effectiveness analyses were used to estimate the costs of screening under three different models. The calculation of costs included actual laboratory costs for the screening and necessary confirmation procedures. Costs of the sociopsychological effects of the screening and for counselling donors who had positive or indeterminate test results were not quantified and are not included in the calculations. The calculation of the benefits of screening (in terms of the morbidity and mortality that were prevented) were based on estimated risks of transmission, disease, and the survival rates of patients in our pilot study who had received transfusions. Transmission risks were estimated from published information[15 16] and our own retrospective study. The risk of developing the disease and the risk of dying as a result of being infected with the virus were estimated from limited published information.[15]