Glucose-6-phosphate dehydrogenase enzyme stability in filter paper dried blood spots

Abstract

Objective: Prior to initial distribution of Glucose-6-phosphate dehydrogenase (G6PD) proficiency testing (PT) materials, we evaluated G6PD enzyme stability in dried blood spots (DBS) under various temperature and humidity environments to develop storage and usage guidelines for our new materials.

Design & methods: We prepared fresh G6PD-normal DBS materials and conducted stability evaluations of daily use and short and long-term storage under various temperature and humidity environments.

Results: G6PD DBS PT materials retained 92% of initial activity after 30days of use at 4°C. Materials stored at -20°C and 4°C with desiccant for 30days retained 95% and 90% of initial activity, respectively. When stored for one year at -20°C or six months at 4°C specimens retained >90% of initial activity. Specimens stored at 37°C with desiccant lost 10% activity in three days. At the end of 30days, specimens stored under 'Extreme'-humidity >50% without desiccant- conditions at 37°C assayed below the NSQAP cut off for G6PD. Humidity exacerbated loss of enzyme activity with increasing temperature and time duration.

Conclusion: Data suggest that G6PD PT materials can be stored at 4°C and used for up to one month and can be stored at -20°C for one year and yield >90% enzyme activity. Exposure to warm temperatures, especially with elevated humidity, should be avoided. Desiccant should always be used to mitigate humidity effects.

Keywords: Dried blood spot; Glucose-6-phosphate dehydrogenase; Newborn screening; Proficiency testing; Stability.

Fig. 1.

G6PD activity in sampling of de-identified newborn specimens mean G6PD activity was 6.1 U/g Hb.

Fig. 2.

G6PD Daily Use G6PD activity decreased by 8% after cycling DBS between 4 °C and RT for 30 days.

Fig. 3.

Short-term stability analysis all specimens maintained > 95% initial G6PD activity under Controlled humidity conditions at −20 °C. Specimens stored at 4 °C under all humidity conditions retained > 90% G6PD activity. Specimens stored at RT under Extreme humidity conditions lost 25% activity. Specimens stored at 37 °C under Extreme humidity conditions lost 80% activity.