Long-term stability of thyroid hormones and DNA in blood spots kept under varying storage conditions

Background: Congenital hypothyroidism is screened using blood spotted on filter paper that may be transported from remote areas to central testing facilities. However, storage conditions and transportation may affect sample quality. Methods: We examined long-term stability of thyroid-stimulating hormone (TSH) and thyroxin (TT4) in blood spotted on filter paper, which was stored at room temperature (RT), 4 degrees C and -20 degrees C under continuous or intermittent power supply (six hours on and six hours off around the clock.) Hormone levels in the discs were measured periodically for up to ten years. Extraction of DNA from blood spots and polymerase chain reaction were performed. Results: Our results showed that TT4 was stable for up to 6.1, 5.34 and 5.16 years when stored at -20 degrees C, 4 degrees C and RT, respectively. TSH was stable for up to 2.7 years at RT, and for up to 6.5 and 4.1 years when stored at -20 degrees C and 4 degrees C, respectively, under continuous power supply. However, under intermittent power supply, TSH was stable for up to 3.8 and 2.5 years when stored at 4 degrees C and -20 degrees C, respectively. Mitochondrial cytochrome oxidase and sex-determining region of Y chromosome genes were successfully amplified from DNA extracted from the blood spots. Conclusion: Our data indicate that TT4 and TSH are most stable in blood spots stored at -20 degrees C under continuous power supply. However, they can be stored at RT or at 4 degrees C and -20 degrees C under interrupted power supply for at least 2.5 years. Moreover, the DNA extracted from the blood spots was intact and suitable for genetic studies.