Why is analysing a patient's urine useful for a doctor?

A urine test (urinalysis) assesses the components of a patient’s urine. This can include examining urine visually, chemically and microscopically. Urinalysis tests are very common and are a non-invasive method of checking a person’s health. Firstly, a urinalysis is very useful in confirming a potential pregnancy. The hormone which is being tested for is human chorionic gonadotropin (hCG). Once a fertilised egg implants into the uterine wall, hCG is rapidly produced which can be found in both the urine and blood of the mother. In A-level biology, you may have come across how a pregnancy test works. The process is an enzyme-linked immunosorbent assay (ELISA) which identifies a substance through a colour change. When urine of a pregnant individual is applied to a test strip, hCG will bind to primary, mobile monoclonal antibodies which are conjugated to dye enzymes. These hCG-antibody complexes will move along the strip, carrying the enzymes with them until they reach immobile complementary antibodies that are bound to dye substrates. An antibody sandwich will form which enables the enzymes to bind the substrates, resulting in a colour change (blue line). Excess primary antibodies will move to the control zone further along the test strip to trigger another colour change, which is required to show that the test is functioning correctly. Thus, a positive test will show two blue lines. If there is no/too little hCG in the urine, the primary antibodies will move past the secondary, complementary antibodies to the control zone where they will bind tertiary antibodies that trigger a colour change. Here, only one blue line will show. A urinalysis is also useful in the later stages of pregnancy as it can reveal gestational diabetes if there are high levels of sugars in the urine. Additionally, if higher levels of proteins are found in the latter stages of pregnancy in combination with high blood pressure, this may indicate preeclampsia.

A urinalysis is useful for diagnosing problems such as infections or kidney issues. It can also uncover the need for further investigation of more serious diseases such as diabetes or liver disease. For example, a high concentration of urine can simply indicate dehydration. An abnormal concentration of ions such as Na+ and K+ may suggest kidney issues. Excessive glucose in urine is a common sign of diabetes and crystals in the urine (crystalluria) may indicate kidney damage. Bilirubin (the yellowish pigment component of bile) in urine is suggestive of liver or bile duct disease. Moreover, urinalysis can confirm whether a patient has a urinary tract infection if pathogens and/or white blood cells are present in the urine. Another reason for conducting a urinalysis is to screen for drugs. These are just a few examples of how analysing urine can help inform a doctor of a patient’s overall health, help diagnose an issue or monitor a medical problem.