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Kidney Stones

Update in Diagnosis and Management

Supersaturation Index

Slide 7

February 2010

This slide pictorially depicts the concept of supersaturation. Supersaturation always exists in relationship to a specific crystal type. A solution is saturated for a specific phase if a crystal of that type neither dissolves nor grows when placed into the solution. The solution is under saturated if the crystal dissolves, and supersaturated if it grows.

In practice, we use a computer program called Equil2 to calculate the theoretic supersaturation of urine in relationship to crystals that can produce kidney stones. Equil2 has the binding coefficients for all common ion pairs that exist in urine, and the program goes through an iterative process to satisfy all of these binding pairs at once, each to the greatest extent possible. Equil2 reports in two scales. One is the relative supersaturation (or RSS scale). In this scale an RSS of 1 indicates a solution is exactly at saturation. The other scale is the exponential DG scale; DG is an abbreviation for a delta Gibbs free energy term. In this scale a DG value of 0 indicates an exactly saturated solution.

Supersaturation Index


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