Minimizing false positive diagnoses in newborn screening for galactosemia

Area of Science:

• Biochemistry
• Clinical Diagnostics
• Newborn Screening

Background:

• Galactosemia diagnosis relies on measuring galactose-1-phosphate uridyltransferase (GALT) activity in dried blood spots.
• Environmental factors like heat and humidity can affect GALT activity, potentially leading to inaccurate results.
• False positive diagnoses of galactosemia can cause unnecessary parental anxiety and further testing.

Purpose of the Study:

• To investigate the impact of heat and humidity on GALT activity in mailed blood spots.
• To identify optimal methods for preserving GALT activity during sample transport and storage.
• To differentiate between true galactosemia and sample deterioration.

Main Methods:

• Blood spots were exposed to varying conditions of heat and humidity.
• Galactose-1-phosphate uridyltransferase activity was measured fluorometrically.
• Phosphoglucomutase activity was simultaneously determined to assess sample integrity.
• Different drying and sealing methods for blood spots were evaluated.

Main Results:

• Both heat and humidity significantly reduce GALT activity in blood spots.
• Allowing blood spots to dry completely before sealing in plastic bags preserves GALT activity.
• Sealing moist blood spots in plastic bags exacerbates GALT activity loss.
• Fluorometric assays with simultaneous phosphoglucomutase determination accurately distinguish between sample deterioration and true galactosemia.

Conclusions:

• Heat and humidity are primary causes of reduced GALT activity in mailed blood spots, leading to false positive galactosemia diagnoses.
• Proper sample handling, including complete drying and appropriate sealing, is essential for reliable GALT activity testing.
• Simultaneous measurement of phosphoglucomutase activity provides a critical control for sample quality in galactosemia screening.