Table 2.

Total urea synthesis and the transfer of ¹⁵N from [5-¹⁵N]glutamine to urea in control subjects and patients with disorders of the urea cycle of varying severity

Subject category	Urea flux, μmol/(kg⋅h)	Glutamine flux, μmol/(kg⋅h)		Transfer of glutamine to urea, percent dose
Healthy controls	131  ± 21	380  ± 63	0.42  ± 0.06	27.9  ± 7.2
Null patients	82  ± 17‡	456  ± 103§	0.003  ± 0.007***	−0.2  ± 1.2***
Partial OTC males	97  ± 45*	454  ± 51	0.16  ± 0.04***	6.8  ± 2.4***
Symptomatic OTC females	108  ± 9	442  ± 68	0.18  ± 0.01***	9.3  ± 1.8***
Asymptomatic OTC females	99  ± 27*	380  ± 89	0.26  ± 0.04***,†	12.6  ± 2.8***,†
ASLD heterozygous carriers	100  ± 15*	373  ± 28	0.35  ± 0.11*	13.7  ± 4.3***
ASSD heterozygous carriers	108  ± 36	282  ± 46	0.22  ± 0.03***	14.3  ± 8.4**

Differences from control values are indicated; *, P < 0.05; **, P < 0.01; ***, P < 0.001. Differences from symptomatic OTC females: †, P < 0.01. 

^‡ Reflects urea synthesis from therapeutic arginine or citrulline. When this is taken into account endogenous urea synthesis was −0.7 ± 16 μmol/(kg⋅h). 

^§Reflects the effect of Ucephan on glutamine flux.