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May 214 min read

Why choose urine over blood?

Updated: Jun 4

Urine and blood are two different bodily fluids that can provide valuable information about a person's fitness or health, but they are often analysed for different reasons.




The urine

Urinalysis plays a crucial role in a number of areas of health, from diagnosing and treating illnesses, examining organ functions, detecting drug use, assessing hydration and physical stress, to confirming pregnancy. As a direct reflection of the substances present in the blood, urine offers a wealth of information about our state of health. This is largely due to the importance of the kidneys in the elimination process, which allows substances that are soluble in water or made soluble by chemical reactions to be excreted in the urine.

Urinalysis mainly involves assessing the chemical composition of the urine, including the detection of molecules such as sugar, proteins, ketones, etc. Urinalysis can also identify the abnormal presence of cells (blood, white blood cells, epithelial cells, etc.) and micro-organisms (bacteria, yeast, etc.). The presence of these elements in the urine can reveal various health problems such as diabetes, urinary tract infections and liver or kidney disorders, but it can also reveal important information relating to the impact of the environment on the body, for example during physical exercise or exposure to specific environmental conditions (altitude, extreme heat/cold, etc.). Urine examination also provides information on the concentration of these dissolved molecules, cells and micro-organisms, as well as their degree of dilution in the urine, which can help to assess, among other things, renal function and the body's hydration level.

The urine is collected by the patient in a sterile container, usually at home or in a laboratory. The sample is then sent to the laboratory for analysis.


The blood

Blood tests, like urine tests, can be used to detect drug use and the presence of abnormalities in the blood, to improve training and recovery from physical exertion, to detect certain nutritional deficiencies, to diagnose certain diseases and to assess organ functions.

Blood analysis often includes an assessment of blood components such as red blood cells, white blood cells and platelets, as well as parameters such as haemoglobin, haematocrit and erythrocyte indices, ... It is also prescribed to assess the levels of various biochemical substances such as sugar, lipids (cholesterol, triglycerides), liver enzymes (ALAT, ASAT), kidney function markers (urea, creatinine), etc. Analysis therefore helps to provide information on metabolisms and organ functions, and to diagnose a wide range of medical conditions such as cardiovascular disease, liver disease, autoimmune diseases, infections, hormonal disorders, cancers, and many others. Blood analysis can also include immune tests such as lymphocyte counts and measurement of specific antibodies, which can help diagnose autoimmune disorders, infections and allergies. It also helps to support athletes in their training and nutrition programmes, to help them perform at their best. It is the health professional who determines the analyses to be carried out, taking into account the objective set for the blood test.

Blood is usually taken in a specialist laboratory.


In brief

Urinalysis focuses mainly on the components and characteristics of the urinary system, while blood analysis provides a more comprehensive view of the body's health, including information on blood circulation, metabolisms and the immune system. The main differences are :

  1. Specific information: Urine and blood provide different information about a person's state of health. For example, urine analysis can detect the presence of certain substances such as proteins, red blood cells, bacteria or abnormal cells, which may indicate kidney, urinary or other problems, whereas blood analysis can assess the levels of these substances.

  2. Non-invasive: Collecting urine samples is generally less invasive than collecting blood samples, making it easier for patients to perform; less stressful, less painful.

  3. Fast: Urine collection requires minimal preparation and can be easily integrated into everyday life, unlike blood sampling, which requires a trip to the laboratory.

  4. Cost: Urine tests can often be less expensive than blood tests, making them a more economical option for certain screening or follow-up tests.

  5. A regular resource available: an adult produces between 1.5L and 2L of urine per day, which corresponds to 5-7 micturitions per day, or a volume of 200 to 250ml/micturition. It is therefore easier to carry out a urine test than a blood test.

  6. Health monitoring: Certain illnesses or conditions can be more easily monitored through urinalysis. For example, people with diabetes can monitor their blood sugar levels using special urine test strips. It is also possible to use these analyses for personal monitoring during a physical training programme (preparation for a competition, optimising training and recovery, etc.), as well as for nutritional monitoring to highlight the diet applied and improve it as required (for physical training, in the event of deficiencies, etc.).

  7. Early detection: In some cases, the substances or cells present in urine can be a means of early detection of illnesses or health problems, particularly when there is a low quantity of molecules present in the blood.

However, it is important to note that urine and blood tests are often complementary and can be carried out in parallel to obtain a more complete picture of a person's health or state of fitness. Decisions about which tests to carry out often depend on the patient's symptoms, medical history and the treating doctor's recommendations.


 
Sources

Desgrandchamps F., "Uriner 10 fois par jour : normal ?", La revue du Praticien, 2020, https://www.larevuedupraticien.fr/article/uriner-10-fois-par-jour-normal

Fletcher J., "All blood tests", Medical News Today, 2020, https://www.medicalnewstoday.com/articles/blood-tests#what-to-expect

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