| Abstract|| |
During the period from January 1995 to January 1996 blood units from 8747 blood donors were screened for blood-borne viruses at King Khalid University Hospital, Riyadh, Saudi Arabia. These tests included HBsAg, antibodies to hepatitis C virus (anti-HCV), antibodies to human immunodeficiency viruses (anti-HIV-1/2). During the same period 1500 blood units were screened for antibodies to human T-cell lymphotropic virus type 1 (anti-HTLV-1). Among the 8747 blood donors, 2.7% were found to be HBsAg-positive on initial screening but 2.2% were confirmed as HBsAg-positive. Regarding HCV, 2.8% were anti-HCV-positive on initial screening but the percentage dropped down to 1.6% on confirmation and only 12 (0.14%) were considered indeterminant by line immunoassay. None of the donors was confirmed anti-HIV positive but five were diagnosed as indeterminant by western blot. Only four were anti-HTLV- I - positive on initial screening but were diagnosed as indeterminant by western blot. In total, 492 (5.6%) of the blood units tested were reactive for any one of the four viruses on screening but only 327 (3.7%) were confirmed positive. All 492 blood units were not recommended for transfusion. This raises the question of the usefulness of confirmatory testing in blood donation. We believe the confirmation is only important for counseling the donor and a non-reactive result on confirmation should not interfere with the decision of not recommending the blood for transfusion.
|How to cite this article:|
Arif MW. Importance of confirmatory testing in donated blood. Saudi J Gastroenterol 1998;4:76-80
Hepatitis C virus (HCV)  was recently identified as the major causative agent of transfusion non-A, non B hepatitis , and diagnosis of infection has been made possible by the development of an anti-HCV assay  . The availability of commercial assays for the detection of antibody to HCV (anti-HCV) made it possible to blood banks worldwide to screen for anti-HCV on donated blood in addition to screening for hepatitis B surface antigen (HBsAg) and antibody to human immunodeficiency virus (anti-HIV). Recently, some countries such as the United States demanded screening for another virus, human T-lymphotropic virus type 1 (HTLV-1) , which also can be transmitted to transfusion recipients , . It is universally recommended that a unit of blood which is found to be reactive for any one of the above-mentioned blood-borne viruses should not be issued for transfusion. In most cases, assurance of reactivity of the blood unit needs retesting and continuation by additional test(s). Some blood banks, however, prefer a cautious approach and recommend that units of blood which are reactive on screening should not be given irrespective of the results of the confirmatory tests. In this paper we review a one year experience of blood screening at a major university hospital blood bank and discuss the importance of confirmation and its practical significance.
| Patients and methods|| |
During one year period from January 1995 to January 1996, 8747 people (8202 males, 545 females; age range 17-55 years; mean 38±3) donated blood at King Khalid University Hospital (KKUH), Riyadh. The majority of the donors (7732, 88.4%) were Saudis and 11.6% were of other nationalities. All donated blood was screened for HBsAg,, anti-HCV, and anti-HIV. The screening was performed using commercially available enzyme immunoassay (EIA) kits: Hepanostika HBsAg Uni-Form II from Organon Teknika (NL-5281 RM Boxtel), United Biomedical Inc. (UBI) HCV EIA 4.0 from Beijing United Biomedical Co., Ltd., and Vironostika HIV Uni-Form II from Organon Teknika. Screening for the three tests was done on LaboTech which is a walk-away automatic diagnostic analyzer system using the EIA application.
All samples which were reactive on screening were repeated in duplicate and then confirmed. Confirmation of HBsAg was done using the confirmatory neutralizing antibody tests from Organon Teknika. Confirmation of anti-HCV was performed using LiaTek HCV III (Organon Teknika) which is a line immunoassay based on a "sandwich" principle. The test detects specific antibodies that are directed against a number of HCV proteins corresponding to the most conserved encoding regions of the viral genome (E2/NS 1, NS3, NS4, NS5 and core proteins). Confirmation of anti-HIV-reactive samples was performed by the western blot assay using HIV Blot 2.2 for the detection of antibodies to HIV-1 and HIV-2 from Diagnositc Biotechnology (Pte) Ltd., Singapore Science Park, Singapore 0511.
During the one year period 1500 blood donors were chosen at random and tested for anti-HTLV-1 by EIA assay from Abbott Laboratories (Abbot HTLV1 2.0 EIA). Confirmation of reactive samples was performed using western blot assay from General Diagnostics Pte Ltd., Singapore 118259 (HTLV Blot 2.4). Manufacturer's instructions were followed in all screening and confirmatory tests.
| Results|| |
The results of HBsAg, anti-HCV, anti-HIV, and anti-HTLV-1 screening on blood donors at KKUH during the one year period are shown in [Table - 1]. Among 8747 blood donors screened HBsAg carrier rate was 2.7% on initial screening and 2.2% only were confirmed HBsAg-positive. On initial screening 2.8% of the 8747 blood donors were anti-HCV-positive but this percentage dropped down to 1.6% after confirmation, and only 12 (0.14%) units of blood were considered indeteuninant. Among the 12 indeterminant ones, six had the core band by LiaTek while four had NS5 band and two had the NS4 band only. Only five units of donated blood were anti-HIV-positive on screening but could not be confirmed by western blot and were considered indeterminant. Similarly all the 1500 units of blood screened for anti-HTLV-1 were negative and the four samples which were anti-HTLV-1-positive on initial screening could not be confirmed and were considered indeterminant by western blot.
| Discussion|| |
The results of this study show that HBsAg carrier rate is 2.2% which is considerably lower than 7-9% carrier rate reported 10 years earlier , . The reduction in HBsAg carrier rate among Saudi blood donors could be due to many factors including the exclusion of previous carriers from the blood donation pool, decrease in exposure to HBV due to the public awareness about hepatitis B virus (HBV) infection in Saudi Arabia, and the effective nationwide vaccination program against HBV started by the Ministry of Health in 1990  . Using third generation EIA tests for screening transfusion blood for HBsAg makes the blood supply in Saudi Arabia safe and eliminates the risk of infection by HBV via the blood transfusion route.
Among our 8747 blood donors, 247 (2.8%) were anti-HCV-IgG-positive on initial screening, 137 (1.6%) were confirmed HCV-IgG positive and 12 (0.14%) were reported as indeterminant. In contrast to HIV and HTLV-1, anti-HCV-reactivity does not necessarily mean that the blood is infectious. Furthermore, because of the nature of the cross, reactivity of the anti-HCV tests available ,,, reactivity should be confirmed. Ideally, when a blood sample is anti-HCV-reactive by EIA, a repeat sample should be tested in both an alternative EIA and supplementary assay before a final result is reported. Testing by an alternative EIA is not always feasible as this necessitates additional machines and reagents and therefore, additional cost. Supplemental assay on the other hand is necessary and this is routinely done in most laboratories involved in screening blood for transfusion. Supplementary assays to be used should use different antigens other than the ones used in the EIA assay to be regarded as true confirmatory tests  . Problems with interpretation of confirmatory tests arise when indeterminate results (only one band) are obtained  , particularly in blood samples from otherwise normal individuals such as blood donors. Only polymerase chain reaction (PCR) will determine whether the blood has HCV-RNA i.e., infectious or not  . PCR, however, remains the most popular tool for genomic detection but for various reasons is not applicable to routine donor screening  .
HTLV-1 is endemic in the Caribbean  southeastern Japan  and some areas of Africa  Central and South America  , and recently described in Central and Northern Australia  . Screening for anti-HTLV-1 in endemic areas is justified but a debate still surrounds the issue of whether or not to screen for anti-HTLV-1 in countries where the virus is not endemic  . In Saudi Arabia, the Ministry of Health started screening for anti-HTLV-1 in blood banks a year ago. However, the data gathered from other Saudi hospitals that applied anti-HTLV-1 screening few years earlier point to the cost-ineffectiveness for routine screening for anti-HTLV-1 in the Saudi population ,,, .
None of the 8747 blood units screened in this study was anti-HIV-1/2-positive. All five samples which gave reactive reading on screening were considered indeterminate by western blot irrespective of the criteria used (World Health Organization, American Red Cross, or US Food and Drug Administration). Three out of the five samples had only GaG protein (P18), and two had a polymerase protein (P55). Four of the donors were followed up for a year with clinical and laboratory evaluation every three months and there was no change in the number of bands in the western blot done and none had any evidence of clinical HIV infection. These results confirm earlier studies , of the low endemicity of HIV in the Saudi population.
In total 492 (5.6%) blood samples were reactive for any of the four viruses we screened for, but only 327 (3.7%) were confirmed reactive and 21 (0.24%) were labeled as indeterminate. Although all the screening tests used were of high sensitivity and specificity, 165 (1.9%) of the blood samples could not be confirmed as reactive, and the blood units were not recommended for transfusion. The failure to confirm the infectivity of those samples could not be clearly identified and only a PCR-based viral test will show whether an EIA-positive but confirmatory-negative sample is infectious or not. Unfortunately, PCR is not routinely used in most blood banks at the present time  . We believe that confirmation is only important for counseling purposes and its interpretation should await repeated testing and clinical follow-up of the patient for a certain period of time. A non-reactive results on confirmation should not interfere with the decision of not recommending the blood unit for transfusion and 1.9% loss of donated blood is not a high price for a safe blood transfusion pool.
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Mohammed Abdul Wahed Arif
Department of Pathology (32), College of Medicine, P.O. Box 2925, Riyadh 11461
Source of Support: None, Conflict of Interest: None
[Table - 1]