hello dear thanks for your query at health care magic. orthostatic poteinuria is most common cause of persistent protenuria in school aged children, occurring in 60 % persistant protenuria. child with this conditionn is usually asymptamtic and condition is discovered on routine urine analysis. the cause for this disorder is unknown patients with this condition excrete proteins upto 10 folds normal in standing position and upto 1gram protein per day. simple lab test can diagnose this condition 1 . get complete urine examination and spot protein to creatinine ratio, 24 hour urine proteins 2 . collect urine every day morning in for three days by keeping child fully empty bladder before going to bed then collect first voided urine sample immediately up on arising in the morning. if its orthostatic protenuria complete urine examination should be with in normal limits , protein to creatinine ratio three urine samples collected should be negative for spot urine protein test or dip stick . if any abnormality in these test please consult nephrologist hope this will help you regards .