Quality control material for activity determinations of urinary enzymes

Area of Science:

• Clinical Chemistry
• Biochemistry
• Enzymology

Background:

• Accurate enzyme activity measurement in urine is crucial for diagnosing various medical conditions.
• Long-term storage of urine samples can affect enzyme stability, impacting diagnostic reliability.
• Standardized methods for preserving urine enzyme activity during storage are needed.

Purpose of the Study:

• To evaluate the long-term stability of five key urinary enzymes stored at -20°C.
• To assess the efficacy of albumin and ethylene glycol as stabilizing agents for urine samples.
• To determine the impact of storage conditions on enzyme activity over a 12-month period.

Main Methods:

• Urine samples were subjected to gel filtration and supplemented with albumin, ethylene glycol, or both.
• Enzyme activity of N-acetyl-beta-D-glucosaminidase, alanine aminopeptidase, alkaline phosphatase, gamma-glutamyltransferase, and lysozyme was measured monthly.
• Stability was assessed using linear regression analysis of enzyme activity over time.
• Storage was maintained at -20°C for 12 months.

Main Results:

• N-acetyl-beta-D-glucosaminidase, alanine aminopeptidase, alkaline phosphatase, and lysozyme showed stability for approximately one year under tested conditions (within 10% change).
• Gamma-glutamyltransferase exhibited instability over the 12-month storage period.
• Albumin and ethylene glycol, alone or in combination, generally supported enzyme stability, with caveats for ethylene glycol's potential method-specific inhibition.

Conclusions:

• Most tested urinary enzymes are stable for up to one year when stored at -20°C with albumin or ethylene glycol.
• Ethylene glycol can serve as a stabilizer but requires careful consideration of its potential inhibitory effects in specific assay methods.
• Gamma-glutamyltransferase stability is a concern, necessitating further research into optimal preservation strategies.