What are 3 possible causes of false positive reactions with presumptive screening test for blood?

Three possible causes of false positive reactions with presumptive screening test for blood are:

1) Antigen contamination: The presumptive screening test for blood detects the presence of haemoglobin, which is a protein found in red blood cells. However, some other substances, such as certain foods, medications and cleaning products, can also contain haemoglobin or haemoglobin-like substances. These substances can contaminate the test sample and cause a false positive result.

2) Cross-reactions: The presumptive screening test for blood is designed to react specifically with haemoglobin. However, some other substances, such as certain chemicals and biological compounds, can also react with the test reagent. These cross-reactions can cause a false positive result.

3) Technical errors: Errors during the collection or handling of the test sample, or errors in the performance of the test itself, can also lead to a false positive result.