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Thyroglobulin assay in fluids from lymph node fine needle-aspiration washout: influence of pre-analytical conditions
Florence Boux de Casson1, Valérie Moal1, Anne-Sophie Gauchez2
1Département de biochimie et génétique, CHU, Angers, France, Groupe de biologie spécialisée de la Société française de médecine nucléaire, Paris, France.
Insights
Thyroglobulin measurement uncertainty in fine-needle aspiration (FNA) washout is linked to pre-analytical factors. Non-specific adsorption in storage tubes significantly impacts results, especially in saline solutions without proteins.
Area of Science:
- Clinical Chemistry
- Analytical Chemistry
- Biochemistry
Background:
- Thyroglobulin (Tg) measurement is crucial for diagnosing and monitoring thyroid conditions.
- Fine-needle aspiration (FNA) washout is a common method for obtaining samples for Tg analysis.
- Pre-analytical factors can significantly influence the accuracy of laboratory test results.
Purpose of the Study:
- To evaluate pre-analytical factors affecting thyroglobulin measurement uncertainty in FNA washout fluids.
- To investigate the stability of thyroglobulin in different storage conditions and solutions.
- To identify the causes of variability in thyroglobulin recovery rates.
Main Methods:
- Studied pre-analytical stability of 41 thyroglobulin samples (FNA washout or standard) in saline and albumin buffer.
- Assessed thyroglobulin concentrations over time under various storage conditions (room temperature, different tubes).
- Investigated the impact of sample concentration and protein content on thyroglobulin recovery.
Main Results:
- No change in thyroglobulin concentration was observed in albumin-containing buffer across all tested storage conditions.
- In albumin-free saline, thyroglobulin recovery was significantly affected by initial concentration and storage duration.
- Non-specific adsorption of thyroglobulin to storage tubes was identified as the primary cause of decreased recovery, dependent on sample protein concentration.
Conclusions:
- Non-specific adsorption in storage tubes is a major contributor to uncertainty in thyroglobulin measurements from FNA washout in physiological saline.
- The presence of plasma proteins does not always prevent this adsorption.
- Using a protein-containing buffer, provided by the laboratory, is recommended for FNA washout samples to ensure accurate thyroglobulin measurement.
Abstract:
The aim of this study was to evaluate the pre-analytical factors contributing to uncertainty in thyroglobulin measurement in fluids from fine-needle aspiration (FNA) washout of cervical lymph nodes. We studied pre-analytical stability, in different conditions, of 41 samples prepared with concentrated solutions of thyroglobulin (FNA washout or certified standard) diluted in physiological saline solution or buffer containing 6% albumin. In this buffer, over time, no changes in thyroglobulin concentrations were observed in all storage conditions tested. In albumin free saline solution, thyroglobulin recovery rates depended on initial sample concentrations and on modalities of their conservation (in conventional storage tubes, recovery mean was 56% after 3 hours-storage at room temperature and 19% after 24 hours-storage for concentrations ranged from 2 to 183 μg/L; recovery was 95%, after 3 hours or 24 hours-storage at room temperature, for a concentration of 5,656 μg/L). We show here that these results are due to non-specific adsorption of thyroglobulin in storage tubes, which depends on sample protein concentrations. We also show that possible contamination of fluids from FNA washout by plasma proteins do not always adequately prevent this adsorption. In conclusion, non-specific adsorption in storage tubes strongly contributes to uncertainty in thyroglobulin measurement in physiological saline solution. It is therefore recommended, for FNA washout, to use a buffer containing proteins provided by the laboratory.
