THE CONSULTANTS' CHOICE: Option E
We recommend all of the above options.
The mother returns the following day with the original diaper and a urine specimen obtained overnight. At about 4 am, the mother changed the baby's diaper, put on a urine bag, and then breast-fed the baby. The urine bag was full when the mother checked the diaper 3 hours later. The mother placed the urine specimen in a container in the refrigerator until she left for the clinic.
The reddish-stained diaper from the previous morning was still heavy with urine in the absorbent matrix. However, the inside surface of the diaper had dried to reveal a fine layer of a rust-colored powder.
The first-morning urine had a pH of 5 and a specific gravity of 1.02, and was negative by dipstick for blood. The centrifuged urine had pinkish orange sediment at the bottom of the tube. The microscopic urine specimen revealed numerous uric acid crystals but no blood.
The mother advised that the baby had not experienced any colicky discomfort and that there was no family history of gout, kidney stones, or metabolic or neurologic problems.
The reddish stain in the diaper is caused by uric acid crystals. The excretion of uric acid in urine is high at birth and falls during childhood until adolescence, when adult levels are observed. Uric acid excretion is especially high during early infancy. The solubility of uric acid is about 12 mmol/L at a urine pH of 8, but only 1 mmol/L at a pH of 5. As such, acid urine favors precipitation of uric acid crystals. The high protein content of breast milk favors acid urine.
Although uric acid crystals are commonly observed in the diapers of infants and are not usually a concern, some rare and more serious disorders of purine metabolism might also present in this fashion. A variety of inherited enzyme deficiencies and renal tubular problems can lead to hyperuricosuria. Deficiency of hypoxanthine- guanine phosphoribosyltransferase is the most commonly reported problemand can present along a clinical spectrum that includes Lesch-Nyhan syndrome at the severe end. Crystalluria with dysuria, stone formation with colicky pain, acute renal failure from urate nephropathy, and severe neurologic impairment are possible problems in children with Lesch-Nyhan syndrome.
Investigations are generally not required for otherwise well infants with uric acid crystals in the urine. However, blood tests for levels of serum uric acid, creatinine, and electrolytes, as well as an ultrasonogram of the kidneys and bladder, should be considered in those infants with uric acid crystals in the diaper who have a family history of gout, kidney stones, or metabolic problems during infancy; a history of colic or dysuria; or evidence of red blood cells in the urine in addition to uric acid crystals.
The problem is self-limited in otherwise well infants who have uric acid crystals in the urine--and no treatment is usually necessary. However, uric acid crystalluria can be associated with dysuria. Maintenance of good hydration will minimize this possibility.