Important: This infographic is educational and does not diagnose conditions. BH4 results should be interpreted by your metabolic specialist together with phenylalanine (Phe), clinical history, and other tests.
Block 1
BH4 basics & the big group differences (PBD vs Healthy vs PKU)
BH4 basics & the big group differences (PBD vs Healthy vs PKU)
BH4 (tetrahydrobiopterin) is a natural helper molecule used by several enzymes. One key enzyme is phenylalanine hydroxylase (PAH), which helps break down phenylalanine (Phe).
• PKU values shown are for age > 2 years (also from the morning window).
• For primary BH4 deficiency (PBD), BH4 was below the test’s quantification limit in the study (<0.5 ng/mL; LLOQ 0.5).
Plasma BH4 by group (labels always visible)
Bars are scaled to 10 ng/mL for easy comparison. Exact values are displayed on each bar.
Block 2
Best time to test (BH4 has a daily rhythm)
Best time to test (BH4 has a daily rhythm)
In healthy adults, BH4 showed a circadian (daily) rhythm—lower in the morning and higher later in the day. The most stable (lowest + least variable) window in the analysis was 07:00–10:59.
- Try to test at the same time of day each visit.
- If your timing changes (morning vs afternoon), ask your clinic before comparing results.
- BH4 is sensitive in blood samples — labs use specific handling to stabilize it.
Healthy adults (07:00–10:59)
This window had the richest data and was used for most comparisons in the study.
Healthy adults (19:00–22:59)
Values were higher later in the day in the study’s healthy adult dataset.
Block 3
Age pattern in PKU (what this dataset suggests)
Age pattern in PKU (what this dataset suggests)
In participants with PKU, BH4 was lower in children ≤2 years and higher after age 2, where it appeared relatively stable in this dataset. (The ≤2 years group included fewer participants.)