You are correct. The excretion of uric acid is high at birth and falls w/ age. Because breast milk acidifies urine during the neonatal period, uric acid can precipitate and present as red/orange discoloration (vs dark green meconium). In an otherwise healthy infant, this discoloration is not usually concerning, and no tests are required. To differentiate from hematuria or hematochezia, uric acid (unlike blood) usually turns into a fine powder when dry, which was evident on this pt’s diaper. Other causes of red/orange diaper include rifampin, beets, and dehydration causing more concentrated urine. In females, vaginal withdrawal bleeding can cause similar discoloration when the child is no longer exposed to maternal hormones. More serious causes include congenital syndromes that cause hyperuricosuria (eg, Lesch-Nyhan syndrome), acute porphyrias, and Serratia marcescens infxn of the GI tract.

Emergency Medicine Journal 2019;36:594-634.