Urine contains water, urea, mineral salts, and the breakdown products of a range of chemicals, including hormones and any toxins taken into the body.

Monoclonal antibodies are antibodies from a single clone of identical cells that are produced to target particular cells or chemicals in the body.

Modern pregnancy tests detect human chorionic gonadotrophin (hCG), which is produced by the developing placenta, in the urine using monoclonal antibodies.

Anabolic steroids are drugs that mimic the action of the male sex hormone testosterone and stimulate the growth of muscles.

A urine test for drug use involves testing for the presence of drugs or their breakdown products.

These drugs are filtered through the kidneys and stored in the bladder before their removal from the body during urination, so urine will typically contain any drugs that a person has used.

An immunoassay is a test that uses monoclonal antibodies to bind to a substance, such as a drug or its breakdown products.

They can be used to indicate whether a urine sample contains drugs or their breakdown products.

Immunoassays are typically the first step in drug testing.

If a person is not pregnant, only one coloured line or pattern appears in the pregnancy test (indicating that the test is working).

If a person is pregnant, two coloured lines or patterns appear in the pregnancy test (indicating that the person has hCG in their urine).

Drugs like anabolic steroids are detected in the urine by vaporising the urine sample with a known solvent.

It is then passed along a tube for gas chromatography and mass spectrometry.

This often follows an immunoassay to confirm the presence of the drug.

1. The wick is soaked in urine, which if a person is pregnant will likely contain the hormone hCG
2. Mobile monoclonal antibodies attached to coloured beads bind to hCG to form an antibody-hCG complex
3. Urine carries this complex to a window with immobilised monoclonal antibodies that only bind to the antibody-hCG complex
4. This forms a coloured line or pattern indicating pregnancy
5. Other immobilised antibodies bind to mobile antibodies with or without hCG, forming a control line

The hCG in the urine binds to the mobile monoclonal antibodies and forms an antibody-hCG complex.