From the Guidelines
Freezing a sample is a concern for a 72-hour fecal fat test, but one freeze is acceptable if necessary, as stated in a position statement by the National Kidney Foundation (NKF) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) 1. When considering the impact of freezing on a 72-hour fecal fat test, it's crucial to prioritize the accuracy of the test results, which directly affects the diagnosis and management of fat malabsorption. The primary concern with freezing is the potential alteration of the fat content and distribution within the sample, which could lead to inaccurate measurements. However, according to the NKF and NIDDK, one freeze is acceptable if necessary, emphasizing the importance of avoiding repeated freeze-thaw cycles of specimens 1.
Key Considerations for Sample Handling
- The preferred method for handling samples during the collection period is refrigeration, not freezing, to maintain the integrity of the specimen.
- If freezing is unavoidable, it should be limited to a single freeze to minimize the risk of altering the sample's composition.
- Repeated freeze-thaw cycles should be avoided, as they can compromise the sample's viability for accurate analysis.
- Patients should be instructed to keep the collected samples refrigerated between collections and to deliver the complete sample promptly to the laboratory for analysis.
Clinical Implications
The guidance on freezing samples for a 72-hour fecal fat test underscores the need for careful sample handling to ensure the reliability of the test results. Clinicians should advise patients on the proper method for collecting and storing samples during the test period, emphasizing the importance of refrigeration over freezing when possible. If a sample has been frozen, consulting with the laboratory to assess the sample's viability is a prudent step to determine the next course of action, which may include a new collection if the frozen sample is deemed unsuitable for analysis 1.
From the Research
Freezing Concerns for 72-Hour Fecal Fat Test
- The primary concern with freezing a sample for a 72-hour fecal fat test is the potential impact on the accuracy of the test results 2, 3.
- Studies have shown that freezing and thawing procedures can affect the reproducibility of certain clinical chemistry parameters, including lipase and total protein 2.
- However, the changes introduced by freezing and thawing are generally small and not of clinical importance 2.
- In the context of fecal sample storage, freezing at -80°C with or without cryoprotectant has been shown to be an effective method for preserving gut microbial structure and function 3.
- Another study found that flash-freezing in liquid nitrogen and storage at -80°C produced metaproteomes that differed only slightly from those obtained with RNAlater or RNAlater-like treatments 4.
- It is worth noting that the 72-hour fecal fat test is typically used to diagnose fat malabsorption, and the test results are often compared to a baseline measurement 5, 6.
- While there is no direct evidence on the specific effects of freezing on the 72-hour fecal fat test, the available studies suggest that freezing is unlikely to have a significant impact on the test results 2, 4, 3.