Overestimation of nuclear matrix protein 22 in concentrated urine.

Objective: 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.

Methods: 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.

Results: 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).

Conclusion: 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.