Excretory Products & Medical Diagnosis (OCR A Level Biology)

Urine tests

• The most common urine test is to look for 'sugar' (glucose) in the urine:
  • All the glucose in the glomerular filtrate should be reabsorbed by the proximal convoluted tubule (PCT) and therefore there should be no glucose present in the urine
  • If a urine test shows that there is glucose present, this suggests that there is something wrong with the person's homeostatic control of glucose (in particular there may be something wrong with the functioning of insulin)

• Urine can also be tested for ketones:
  • Ketones, such as acetone (propanone) and acetoacetate, are produced by the metabolism of people who have diabetes
  • If a urine or blood test shows that there are ketones present, this suggests the person has diabetes mellitus

• Urine can also be tested for proteins:
  • If a urine test shows that there is protein present, this suggests that the person's blood pressure may be too high, or it may indicate a kidney infection or that there is something wrong with their blood filtration mechanism

• Positive tests for nitrate ions in the urine indicate the person has a bacterial infection in the urinary tract

Pregnancy tests

• Urine samples can also be used in pregnancy testing
• Pregnancy testing sticks contain monoclonal antibody molecules that are specific to a hormone produced during pregnancy (that therefore becomes present in the mother's urine)
  • This hormone is human chorionic gonadotropin (hCG), which is secreted by the early embryo after it has implanted in the uterus
  • The antibodies in the testing sticks all originate from a single clone of B lymphocyte cells that all produce the same antibody specific to hCG
  • This minimises the chances of false test results

Monoclonal antibodies are used to detect the presence of the hormone hCG in the urine of pregnant women

Testing for anabolic steroids

• Urine samples can also be used to test for anabolic steroids
• For example, athletes are regularly tested for anabolic steroids as these can be used to rapidly build muscle mass by stimulating protein synthesis
• Anabolic steroids are detected in urine via gas chromatography or mass spectrometry