Effect of repeated freeze-thaw cycles on urinary albumin-to-creatinine ratio

Abstract

Background: Urinary albumin-to-creatinine ratio (UACR) is widely used for diagnosis of chronic kidney disease in population investigation surveys. It is recommended that urinary albumin should be measured as soon as possible after urine is collected. It is not clear whether freezing and thawing affect the value of UACR and it is very inconvenient to measure UACR quickly in a population survey. The current study tries to determine the effect of repeated freezing and thawing on UACR to explore the possibility of freezing urine samples. Methods: Fifty-three urine samples with abnormal urinary albumin (ranging from 22.9mg/L to 891.9mg/L) were selected. The albumin and creatinine were measured before freezing, then all sample were stored at −30°C. After being thawed at room temperature, the albumin and creatinine concentrations were measured again. The samples were frozen and thawed for five times, and albumin and creatinine were measured after each thawing. The measurements of albumin, creatinine, and UACR after each thawing were calculated and compared with its initial values using multiple comparisons of one-way ANOVA. Results: Compared with its initial value, urine albumin, creatinine and UACR all did not show any significant differences (p > 0.05). Conclusions: It is feasible to freeze urine samples for future measurement of UACR. Urine samples can be safely frozen and thawed at least five times.

Key Words::

• Epidemiology
• chronic kidney diseases
• urinary albumin-to-creatinine ratio
• urinary albumin
• urinary creatinine

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.