Urine Creatinine Normalization for Toxins Testing
Creatinine is a waste product produced by muscles from the breakdown of a compound called creatine phosphate. It is filtered out of the blood by the kidneys and excreted into the urine at a relatively constant rate, making it a useful marker for estimating the glomerular filtration rate (GFR), which is a measure of kidney function.
When urine tests are conducted, particularly tests for substances like proteins or other metabolites, the concentration of these substances in urine can vary depending on factors like urine volume and hydration status. To account for these variations and to standardize the results, urine creatinine concentration is often measured alongside the substance of interest. The ratio of the substance concentration to urine creatinine concentration is then calculated, providing a normalized value that helps to account for differences in urine concentration.
Individuals who “hyperhydrate,” consuming excessive intake of water beyond maintenance needs, may have lower urine creatinine than normal. While this may be an unexpected finding in a person with normal kidney function, it is due to excessive consumption of water before the urine specimen collection, and can usually be identified by very clear, diluted, unconcentrated urine that looks like water. However, while a low urine creatinine reflects dilution, it does not skew detection of toxic elements within urine as the laboratory uses creatinine concentration methods to accurately normalize the toxins of interest.
Additionally, while looking at the report on toxins, it is important to keep in mind that Heavy Metals, Environmental Toxins, Mycotoxins, and PFAS Chemicals tests report toxic element levels from the 0-75th, 75th-95th, and greater than 95th percentiles based on the reference populations. In a preventive healthcare setting the goal is to minimize exposure to toxins which is why a percentile-based system is ideal. In a population level comparison of your results individuals may aim to reduce their exposure and be among the bottom 10 percentile for exposure to any toxin. This is to help make healthy lifestyle choices in consultation with their healthcare practitioner to maintain health and wellbeing.
Reference Study
A study examined the controlled ingestion of different volumes of water on urine creatinine levels, after drinking 16.7 ounces, 33.3 ounces, and 50 ounces of water within 15 minutes. As water intake went up, urine creatinine levels went down.
- After drinking 16.7 oz, urine creatine level was 0.60 mg/mL
- After drinking 33.3 oz, urine creatine level was 0.15 mg/mL
- After drinking 50 oz, urine creatine level was 0.10 mg/mL
Additionally, the study identified differences in men and women and the influence of weight on the impact of excessive water consumption. Women tended to have lower levels of urine creatinine (due to their lower muscle mass), and individuals below 132# tended to have lower levels of urine creatinine (also due to their lower muscle mass).
Estimated Fluid Needs
To calculate estimated maintenance fluid needs by weight, use the Evidence Based Medicine Consult Maintenance Fluid Calculator. Please note to convert ml (milliliters) to ounces, divide milliliters by 30. Example, 1,500 ml divided by 30 = 50 ounces.
More Information
See Causes of Low and High Urine Creatinine
Reference
Franz, S., Skopp, G., Boettcher, M., & Musshoff, F. (2019). Creatinine excretion in consecutive urine samples after controlled ingestion of water. Drug Testing and Analysis, 11(3), 435–440. https://doi.org/10.1002/dta.2514
