Long-term urine biobanking: Storage stability of clinical chemical parameters under moderate freezing conditions without use of preservatives

• We examined long-term stability of select urine analytes stored > 10 yr at − 22 °C.
• Urine samples were both collected and stored preservative-free.
• Repeat measurements of more than half of the analytes did not differ from baseline.
• E.g., creatinine, iodine, nitrogen, various minerals proved as stable biomarkers.
• Results suggest high long-term stability for relevant clinical chemical parameters.

ObjectiveTo examine the long-term stability and validity of analyte concentrations of 21 clinical biochemistry parameters in 24-h urine samples stored for 12 or 15 yr at − 22 °C and preservative free.Design and methodsHealthy children's 24-h urine samples in which the respective analytes had been measured shortly after sample collection (baseline) were reanalyzed. Second measurement was performed after 12 yr (organic acids) and 15 yr (creatinine, urea, osmolality, iodine, nitrogen, anions, cations, acid–base parameters) with the same analytical methodology. Paired comparisons and correlations between the baseline and repeated measurements were done. Recovery rates were calculated.ResultsMore than half of the analytes (creatinine, urea, iodine, nitrogen, sodium, potassium, magnesium, calcium, ammonium, bicarbonate, citric & uric acid) showed measurement values after > 10 yr of storage not significantly different from baseline. 15 of the 21 parameters were highly correlated (r = 0.99) between baseline and second measurement. Poorest correlation was r = 0.77 for oxalate. Recovery ranged from 73% (oxalate) to 105% (phosphate).ConclusionOur results suggest high long-term stability and measurement validity for numerous clinical chemistry parameters stored at − 22 °C without addition of any urine preservative. Prospective storage of urine aliquots at − 22 °C for periods even exceeding 10 yr, appears to be an acceptable and valid tool in epidemiological settings for later quantification of several urine analytes.

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