differences between blood and sweat lactate values

As you may have noticed in our previous blogs, the lactate values ​​in sweat are of a different magnitude than those in blood. In this blog we try to explain where this difference comes from.  

Let's start with some examples. In the graph below we see the lactacte concentration measured in blood (red) and the IDRO sweat lactate concentration (blue) before and after a 2400m maximal running test in military recruits. Before the test the values are comparable, but after the test we see higher lactate values in sweat.

Blood lactate versus sweat lactate during a 2400m running test

In the 2nd example below we see the results of an incremental exercise test of a trained runner. During this test we measured sweat lactate continuously with the IDRO sensor and compared it with blood lactate concentration measured after every step. In this test we also see higher lactate values in sweat compared to blood, especially when the values start increasing. In the graph below we used different scales for blood and sweat lactate to make it clearer.  

Continuous correlation between sweat lactate measured with the IDRO device and blood lactate measured with an ABL90 blood gas analyser during a cycling exercise.

Resting blood lactate values normally are between 1-2 mmol/l. During exercise they can rise up to 20 mmol/l. Sweat lactate values have higher values ranging from 1 up to more than 30 mmol/l. It has not yet been scientifically proven where these differences in lactate concentration ​​come from. Here are some explanations for the differences found between sweat and blood lactate concentration:

1. One possible explanation for the higher values ​​in sweat is that the sweat glands themselves also produce lactate locally once you start sweating. This local production in combination with a derivative from the blood ensures that higher values ​​are measured in the sweat than in blood. 

2. Another explanation is contamination of the sweat samples caused by residues from the skin. When sweating old residues containing lactate can cause higher lactate values. This is why we advice to clean the skin before applying the IDRO sensor.

3. Local variation in sweat rate and evaporation can also effect the sweat lactate concentration. Some body parts have a higher sweat gland density and higher sweat rate. This can cause variation in the sweat lactate concentration on different body locations. Therefore it is best to only compare sweat lactate values from the same body location. Sweat evaporation can also cause variations in the sweat lactate concentration. By fixing the IDRO sensor onto the body it stays on the same location and there is no sweat evaporation on the sampling site.

At IDRO we do various studies to determine the origin of lactate in sweat. By using the IDRO sensor we can gain more insight into lactate production in the body, which can have important implications not only for sports, but also for diseases.