In global health programmes, the Enzyme-Linked Immunosorbent Assay (ELISA) is a critical diagnostic tool used to monitor the prevalence of HIV by screening blood samples. In an indirect ELISA test designed to detect anti-HIV antibodies in patient serum, a false-positive result can occur if the procedure is not performed precisely.
Which of the following describes the most likely cause of a false-positive result in this monitoring test?
Insufficient washing of the wells after the addition of the enzyme-linked secondary antibody, leaving unbound conjugate that reacts with the substrate.
A high concentration of active helper TTT-lymphocytes in the patient's serum, which directly bind to the enzyme and trigger a non-specific color change.
Over-washing with a high-salt buffer, which causes the immobilized HIV antigens to denature and bind directly to the color-changing substrate.
Rapid somatic mutation of the patient's primary antibodies during the 37∘C37^\circ\text{C}37∘C incubation phase, converting them into active enzymes.
97 exam-style questions on OCR GCSE Biology 6.3 Monitoring and maintaining health, covering 6.3.1 Health and disease, 6.3.2 Interactions between diseases, 6.3.3 Spread of communicable diseases, 6.3.4 Common infections and diseases, 6.3.5 Physical plant defence responses, 6.3.6 Chemical plant defence responses, 6.3.7 Detecting and identifying plant diseases, 6.3.8 White blood cells and platelets, 6.3.9 Non-specific defence systems, 6.3.10 The immune system, 6.3.11 Monoclonal antibodies, 6.3.12 Vaccines and medicines, 6.3.13 Aseptic techniques, 6.3.14 Discovery and development of new medicines, 6.3.15 Causes of non-communicable diseases, 6.3.16 Treatments for cardiovascular disease, 6.3.17 Lifestyle factors and non-communicable diseases, 6.3.18 Cancer, 6.3.19 Stem cells in medicine, 6.3.20 Gene technology in medicine, and 6.3.21 The human genome and medicine. Each one has a worked solution and a mark scheme showing where the marks go.