Exercise-induced proteinuria is biphasic.13 Increased protein excretion occurs 30 minutes after exercise and is related to changes in intraglomerular hemodynamics and the resulting saturation of the renal tubules. Around 24 hours after exercise, oxidative stress on the glomeruli causes another slight elevation in albumin excretion without changes in β2-microglobulin, thereby indicating glomerular proteinuria exclusively.
Even the pros aren’t exempt. Exercise-induced proteinuria does not decrease with regular physical training. This was demonstrated in a study of 10 well-trained professional cyclists for whom strenuous exercise increased overnight protein excretion of both tubular and glomerular origin despite ongoing regular physical training.14
Creatine supplements do not increase proteinuria. A study of creatine supplementation in animal models noted no changes in 24-hour proteinuria or albumin excretion in both normal and two-thirds-nephrectomized animals.15 Another study compared creatine use with nonuse in athletes who had been training regularly and strenuously (12- 18 h/wk) for 5 to 10 years. They were evaluated for 10 months to 5 years. The groups exhibited equivalent urine excretion rates for albumin and creatinine, with no deleterious effect on kidney function.16
What happens when chronic disease is factored into the exercise equation?
Patients with a 2- to 20-year history of insulin-dependent diabetes without chronic kidney disease (CKD) who exhibited normal albumin excretion at baseline were more likely to develop proteinuria after exercise than healthy controls.17,18 The postulated cause was undetected glomerular changes due to diabetes. An exercise-provocation test may one day be useful in predicting future development of nephropathy, but further studies are needed.19-21
Exercise increases proteinuria immediately in individuals with metabolic disorders like obesity, through a mechanism different from diabetes mellitus. Proteinuria in the obese population is thought to be glomerular in origin, as opposed to both tubular and glomerular proteinuria in diabetic nephropathy.22,23
In CKD, low-intensity exercise long term does not promote proteinuria or lead to rapid progression of CKD. In one study, obese patients (body mass index >30 kg/m2) with diabetes and CKD stage II to IV who exercised 3 times weekly (aerobic training for 6 weeks, followed by 18 weeks of supervised home exercise) increased their stamina and exhibited slight, statistically insignificant decreases in resting systolic blood pressure and 24-hour proteinuria.24 A 12-week low-intensity aquatic exercise program for 26 patients with mild to moderate CKD decreased blood pressure and proteinuria and slightly improved glomerular filtration rate (GFR).25 These results for proteinuria and GFR were shown previously in rats with subtotal nephrectomy.26
Elevated urinary albumin excretion with exercise is significantly higher in patients with acromegaly when compared with normal healthy subjects. The underlying pathology is thought to occur at the glomerular filtration barrier with intact tubular function. Somatostatin analog treatment for acromegaly leads to reductions in postexercise albuminuria.27,28
How to manage suspected exercise-induced proteinuria
When interpreting the meaning of proteinuria detected on routine urinalysis, keep in mind the temporal relevance between exercise and urine collection. If urine is found to have been collected within 24 hours of intense exercise, repeat testing in the absence of prior exercise on at least one other occasion to differentiate between transient and persistent proteinuria. In confirming transient proteinuria after exercise, reassure the patient that it is a benign condition. This holds true as well for routine microalbumin-to-creatinine urine testing in patients with diabetes who exercise. If the result of a repeat test is high, turn your attention to another possible cause of proteinuria, such as diabetic nephropathy.
Screening for proteinuria during sports preparticipation examinations is not recommended because the diagnostic utility is low.29 Researchers performed urine dipstick testing for protein, blood, and glucose in preparticipation assessments of 701 students.29 They detected proteinuria in 40 students and glucosuria in one. Follow-up testing with first-voided morning urine specimens and glucose tolerance testing was normal in all students.
CORRESPONDENCE Fahad Saeed, MD, 313 Brook Hollow, Hanover, NH 03755; email@example.com