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Variability of Urine Gd Measurements- Feb 2021

Gd toxicity and treatment with chelation are relatively uncommon disease-treatment combinations in medicine in that it is possible to measure directly with numerical results, the status of predictors of disease and of the response to treatment. In this way similar to type 1 diabetes and insulin treatment. In contrast, GDD as the example, iv glutathione for treatment, there is no numerical way to see benefit, and lack of Flare, although patients may see as a good thing, probably actually means that nothing is actually happening.

These are the important points to know:

1. There is some intrinsic variability in urine determination of Gd, 24 hr measurements diminishes this, but does not remove it. The sample sent in for analysis is a small volume of the total, and the adequacy of shaking the entire sample, and the volume of the entire sample effect it. Larger volume with more dilute urine have a negative effect on accuracy

2. The amount removed depends on: i) the amount in the body, ii) accessibility, and iii) brand and molecular structure of GBCAs. Variables are: the reservoirs the Gd is in, le Chatelier's re-equilibration, and time between chelations. Example of these effects: shorter interval between chelation allows less re-equilibration so percentage-wise more Gd retained in bone, and hence less removed. Longer intervals have the opposite effect, more transfer from bone to skin (where Gd is easier to remove), and more Gd removal. The more macrocyclic GBCAs that form the body reservoir of Gd, the less removed, usually about 1/2 the amount of the Gd present, compared to linear agents.

3. Even in patients with GDD, 3 months after GBCA injection, especially if it is the sole GBCA ever administered, the urine Gd will approach 0. This does not mean the patient does not have GDD and does not mean the Gd has all left the body. For some reason these misunderstandings are common. This reflects the great majority of Gd left in the body is now imbedded in tissues. I generally therefore always take prechelation urine Gd with a grain of salt, actually a boulder of salt. If the interval between chelations is short the pre-chelation urine Gd will be higher because of recent remobilization of Gd in the body. So proximity of the current prechelation urine to the prior chelation is always an important variable.

I always take all these variables into consideration when evaluating urine Gd values.

Richard Semelka, MD

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