Aim: We sought to determine if an acute kidney injury biomarker, neutrophil gelatinaseassociated lipocalin (NGAL), would be up-regulated by high-intensity proteinuria-inducing exercise. Methods: A prospective cohort design was utilised. 100 healthy, active adults (mean age 24 ± 4 (SD) years) were screened for post-exercise proteinuria (PeP); 10 PeP positive and 10 PeP negative participants then completed a high-intensity exercise protocol involving an 800 meter sprint. Plasma and urinary NGAL, urinary creatinine, urinary albumin and urine volume were obtained at the following time points: pre-run, immediately post-, 25 minutes, one hour and two hours post-run. Results: Following high-intensity exercise, 64% of participants had urinary NGAL concentrations above the normal range, particularly at 25 minutes post (P = 0.002). However, there was no difference in NGAL response between PeP positive and negative groups and plasma NGAL was decreased, not elevated, following exercise (P = 0.002). In some individuals normalizing urinary NGAL for urinary creatinine attenuated elevations. Urinary NGAL was also negatively correlated with urine volume (r = -0.701, P = 0.005). Conclusion: Proteinuria susceptibility did not influence an acute injury biomarker response to exercise. Nevertheless, urinary NGAL was elevated by exercise, possibly due to increased production by the proximal tubule, increased plasma clearance (given the decrease in plasma NGAL) and/or a concentrating effect of exercise-induced oliguria. Until correct normalisation of urinary biomarkers is determined, NGAL should be interpreted cautiously in exercise and acute kidney injury-induced oliguria. The inter-individual NGAL response to exercise also warrants further investigation.

The effects of storage for 6 months or 2 years at -20 degrees C were studied in urine samples from Type II diabetic patients by assaying albumin by immunoturbidity, N-acetylglucosaminidase (EC 3.2.1.30) by methoxynitrovinylphenol release, and creatinine by the Jaffé method. There were significant decreases (P < 0.001) in albumin/creatinine ratios from 1.14 (0.63-2.98) to 0.83 (0.32-2.12) g/mol (median + interquartile ranges) after 6 months (n = 97), and from 1.64 (0.74-5.72) to 1.00 (0.37-4.54) g/mol after 2 years (n = 89). The percentage of samples with results below the detection limit of the albumin assay (2 mg/L) increased from 5% to 21% after 6 months and from 0% to 34% after 2 years. N-Acetylglucosaminidase/creatinine ratios decreased (P < 0.001) from 520 (358-832) to 380 (263-695) U/mol after 6 months and from 520 (330-865) to 258 (82-462) U/mol after 2 years. The effect of storage was greater in samples with concentrations in the normal range (< 2.5 g/mol for albumin/creatinine, < 500 U/mol for N-acetylglucosaminidase/creatinine). Samples with albumin concentrations more than twice the normal range were still detected as abnormal after storage at -20 degrees C; e.g., 18% were > 5 g/mol (albumin/creatinine) initially, with 17% > 5 g/mol after 6 months of storage. We therefore recommend storage of urine samples at 4 degrees C for no longer than 7 days before assay.