The highest urine specific gravity I have ever seen

1.050 is really high. Even the healthiest kidneys can’t concentrate urine past a specific gravity of 1.030. To get this high the urine must contain another substance.

In this patient’s case she had just undergone a heart catheterization. IV contrast is rapidly cleared by the kidney and increased the density of the sample. Proteinuria and glucosuria are other conditions which can cause an abnormally high urine specific gravity.