Human immunodeficiency virus-1 and hepatitis C virus RNA among South African blood donors: estimation of residual transfusion risk and yield of nucleic acid testing.

BACKGROUND AND OBJECTIVES: South Africa is an endemic area for human immunodeficiency virus 1 (HIV-1) infection, which has an impact on the safety of the blood supply. We studied the presence of HIV-1 and hepatitis C virus (HCV) RNA, and recent HIV seroconversion, in blood donors in order to estimate transfusion risk and to determine whether nucleic acid testing (NAT) could effectively improve blood safety. MATERIALS AND METHODS: Unlinked samples collected in 1999 from 9077 HIV-low prevalence (LP) and 10,632 HIV-high prevalence (HP) donors were studied. Donor demographic information and serology results were collected prior to breaking the linkage. All samples were individually tested using a multiplex NAT assay for HIV-1 and HCV RNA. HIV antibody-positive samples were further tested using a 'detuned' (less sensitive) enzyme immunoassay (EIA) procedure to determine whether a donor had recently acquired infection. Data were used to estimate the residual transfusion risk and to project NAT yield. RESULTS: HIV was 45 times more prevalent in the HP- than in the LP donor group; and among the HP group, female donors had a significantly higher prevalence of HIV than male donors. All seven HIV-1 p24 antigen-positive samples in the study were also HIV NAT positive. Two HIV NAT-positive samples were anti-HIV negative; both of these samples were from HP donors. Assuming that 10% of the 900,000 annual donations in South Africa are from the HP group, we projected an annual NAT yield of 8.5 cases over the current screening of antibody and p24 antigen. However, if p24 antigen testing were to be eliminated, this number would be increased to 17 cases per year. Based on 'detuned' EIA results, the incidence rate for HIV infection was estimated at 1.29 and 51.12 per 10,000 per year for the LP and HP donor groups, respectively. Assuming a 15-day earlier detection by HIV NAT compared with antibody tests, these incidence rates project that NAT may intercept an additional 23 (95% confidence interval: 15-33) HIV-positive donations per year. For HCV, two viral RNA and antibody-positive samples (one from the LP group and one from the HP group) and no NAT yield cases were found in the study. CONCLUSIONS: Implementation of routine NAT blood screening would allow elimination of HIV-1 p24 antigen testing and improve the safety of the blood supply in South Africa. However, the cost-benefit ratio of introducing such an expensive technology in a country with a limited health budget will have to be carefully considered.

Platelet turnover and kinetics in immune thrombocytopenic purpura: results with autologous 111In-labeled platelets and homologous 51Cr-labeled platelets differ.

Mean platelet survival and turnover were simultaneously determined with autologous 111In-labeled platelets (111In-AP) and homologous 51Cr-labeled platelets (51Cr-HP) in ten patients with chronic immune thrombocytopenic purpura (ITP). In vivo redistribution of the 111In-AP was quantitated with a scintillation camera and computer-assisted image analysis. The patients were divided into two groups: those with splenic platelet sequestration (spleen-liver 111In activity ratio greater than 1.4), and those with diffuse sequestration in the reticuloendothelial system. The latter patients had more severe ITP reflected by pronounced thrombocytopenia, decreased platelet turnover, and prominent early hepatic platelet sequestration. Mean platelet life span estimated with 51Cr-HP was consistently shorter than that of 111In-AP. Platelet turnover determined with 51Cr-HP was thus over-estimated. The difference in results with the two isotope labels was apparently due to greater in vivo elution of 51Cr. Although the limitations of the techniques should be taken into account, these findings indicate that platelet turnover is not always normal or increased in ITP, but is low in severe disease. We suggest that this may be ascribed to damage to megakaryocytes by antiplatelet antibody. The physical characteristics in 111In clearly make this radionuclide superior to 51Cr for the study of platelet kinetics in ITP.

Zinc-induced platelet aggregation is mediated by the fibrinogen receptor and is not accompanied by release or by thromboxane synthesis.

We demonstrate that zinc (0.1 to 0.3 mmol/L) induces aggregation of washed platelet suspensions. Higher concentrations (1 to 3 mmol/L) of zinc were needed to aggregate platelets in platelet-rich plasma obtained from blood anticoagulated with low-molecular-weight heparin, probably due to the binding of zinc to the plasma proteins. Zinc-induced aggregation of normal washed platelets required added fibrinogen and no aggregation occurred with thrombasthenic platelets or with normal platelets pretreated with a monoclonal antibody (10E5) that blocks the platelet fibrinogen receptor. These data indicate that the platelet membrane fibrinogen receptor-glycoproteins IIb and IIIa mediate the effect of zinc. Zinc-induced aggregation was blocked by the agent TMB-8, which interferes with the internal calcium flux, and by prostacyclin, which elevates platelet cyclic adenosine monophosphate levels. Zinc-induced aggregation was not accompanied by thromboxane synthesis or by the secretion of dense-body serotonin and was not affected by preexposure of platelets to acetylsalicylic acid. Experiments with creatine phosphate/creatine phosphokinase showed that the zinc effect on platelets was independent of extracellular adenosine diphosphate (ADP). Zinc had an additive effect when platelet aggregation was stimulated with subthreshhold concentrations of collagen or ADP. Together with the known effects of nutritional zinc on in vivo bleeding, on platelet aggregation, and on lipid metabolism, the results suggest that zinc may have an important bearing on normal hemostasis, thrombosis, and atherosclerosis.

Kinetics, in vivo redistribution and sites of sequestration of indium-111-labelled platelets in giant platelet syndromes.

Six patients with giant platelet syndrome were examined: four with Bernard-Soulier syndrome (two were asplenic); one with hereditary thrombopathic thrombocytopenia; and one with May-Hegglin anomaly. Autologous platelets were labelled with In-111-oxine and in vivo redistribution and sites of sequestration measured with quantitative imaging. In Bernard-Soulier syndrome platelet survival was normal or moderately shortened; platelet turnover was decreased only in the two patients with thrombocytopenia. In the patients with thrombopathia or May-Hegglin anomaly, platelet survival and turnover was moderately decreased. In those patients with normal-sized spleens, the mean splenic platelet pool consisted of 35.5% of the platelet mass, i.e. normal. The intrasplenic transmit time of the megathrombocytes was prolonged. Splenic blood flow was within normal limits. There was a marked accumulation of platelets in the liver at equilibrium: 15.5-58.8% of whole body radioactivity (normal 9.6 +/- 1.2%). This finding is unexplained. The final sites of sequestration of platelets were mainly in the liver and spleen, similar to that seen in normal subjects. We conclude that there is no inverse relationship between cell size and splenic platelet transit time. Platelet size therefore does not determine the size of the splenic platelet pool. The size of the platelets also does not seem to affect the sites of sequestration at the end of their life span.

Indium-111-labelled human platelets: a method for use in severe thrombocytopenia.

We describe and evaluate a simple method for labelling autologous human platelets with Indium-111-oxine in patients with severe thrombocytopenia. Twenty patients with immune thrombocytopenia and platelet counts ranging from 5 to 119 X 10(9)/1 were investigated. Platelets were isolated from blood by differential centrifugation, residual platelets were repeatedly washed from the red cell layer and buffy coat and labelled with In 111 in saline. A mean of 55% +/- 21 of platelets were harvested from the blood, labelled with 49% +/- 24 efficiency and 15.8 X 10(8) labelled platelets reinjected to the patients. Contamination of the platelets with red cells and plasma was low. The labelled platelets were viable as assessed by in vitro aggregation, recovery in the circulation and mean survival time. This method permits quantitative platelet imaging with autologous labelled platelets in patients with severe thrombocytopenia.

Radiation dose from human platelets labelled with indium 111.

The biological distribution of 111In-labelled platelets in normal subjects was determined by whole-body counting and scintillation-camera computer-assisted imaging. Using these data, organ radiation dose was quantitated. The highest radiation dose of 7.4 mGy/MBq (27.4 rad/mCi) was received by the spleen and 0.97 mGy/MBq (3.6 rad/mCi) by the liver. While body radiation dose was 0.25 mGy/MBq (0.9 rad/mCi). The gonad radiation dose of males was 0.14 mGy/MBq (0.5 rad/mCi) and that of females 0.22 mGy/MBq (0.8 rad/mCi). These estimates indicate that radiation doses received from 8.6 MBq of 111In-labelled platelets are well within acceptable limits, and that 111In is a safe labelling agent for the study of platelet kinetics.