Overestimation of nuclear matrix protein 22 in concentrated urine

To confirm the hypothesis that nuclear matrix protein 22 (NMP22) is overestimated in concentrated urine, we compared the NMP22 values measured at different dietary states.

We retrospectively reviewed 531 healthy subjects who had had abnormal urinary NMP22 values ≥ 10 U/mL at the first test and underwent a second NMP22 test within 2 weeks. The first NMP22 test was performed after overnight fasting, and the second was performed with no dietary restrictions. We compared the NMP22 values between the 2 measurements and investigated the relationship between the NMP22 value and urine specific gravity.

At the second test, 504 subjects (94.9%) had a normal NMP22 value of <10 U/mL and only 27 subjects (5.1%) persistently had an abnormal NMP22 value of ≥ 10 U/mL. Both NMP22 and urine specific gravity at the first test were significantly higher than at the second test (P <.0001). Subjects with an abnormal NMP22 value tended to have a more concentrated urine with a greater urine specific gravity than did the subjects with a normal NMP22 value. This difference was significant in the subgroup undergoing bowel preparation for colonoscopy (P <.001).

NMP22 will be overestimated in concentrated urine after overnight fasting. When interpreting the NMP22 value, we should consider the overestimation of NMP22 in concentrated urine.