Creatinine Correction

What is creatinine?

Creatinine is a chemical that is produced as our muscles use energy. It comes from the conversion of chemical energy (from the food we eat) into mechanical energy (movement). Our bodies produce creatinine at a fairly constant rate. Creatinine is transported through the bloodstream to the kidneys and is excreted in urine. Scientists have discovered that measuring creatinine levels is a good way to evaluate the health of our kidneys.

What is the ug/g creatinine (creatinine corrected) unit and what does it mean?

A challenge with urine samples is that concentration changes throughout the day. As a result, it is hard to understand the measure value of a chemical in the urine without a method to equalize it (laboratorians call this standardizing).

As an example, let’s say that two people had the same exposure to arsenic the day before participating in the biomonitoring project. The first person submitted their urine sample right after getting up in the morning. The first person’s urine was dark yellow and had a chemical measurement of 25 ug/L (25 micrograms per liter). Creatinine is a chemical in urine that has been found to be a useful measure of how concentrated the urine is. The laboratory measures the creatinine level in the first person’s urine and found that it was 1.25 g/L (1.25 grams per liter).

The second person provides their sample later in the day, after drinking several cups of water, and maybe a large caffeinated soda. The second person’s urine sample is almost clear in color. The laboratory measures the chemical at 17 ug/L and creatinine at 0.85 g/L.

Thus, it appears the second participant’s chemical level is lower than the first participant’s. One could conclude that the first person was more exposed than the second person, but we already know this conclusion is wrong. Another conclusion is that the difference in urinary output (concentrated first morning versus diluted later in the day) is affecting the chemical concentration. We can use the creatinine level to adjust for urinary output.

For Person 1: 25 ug/L ÷ 1.25 g/L = 20 ug/g creatinine

For Person 2: 17 ug/L ÷ 0.85 g/L = 20 ug/g creatinine

After correcting for urine concentration, we discover that these two participants had the same chemical exposure level. Now we can more accurately evaluate their exposure risks.

Last Updated: May 1, 2017