creatinine tends to be a biomarker that's more reliable than that of nitrogen or urea. Of particularly GFR, which is the glomerular flow rate or filtration rate. Any issue here, pre-intra or post, that alters filtration can cause AKI. So this is just the end point of the toxins or the metabolic waste products. That's you and your toxins. And we'll talk about how some assessment tools are used to kind of understand what's happening at the kidney level with an AKI.