Age related reference values for urine creatine and guanidinoacetic acid concentration in children and adolescents by gas chromatography-mass spectrometry

A new gas chromatography-mass spectrometry method for routine quantification of urine creatine and guanidinoacetic acid (GAA) has been developed to provide a fast, reliable and inexpensive metabolic screening. Our method uses a two-step derivatization procedure which involves a reaction with hexafluoroacetylacetone followed by a reaction with monotrimethylsityltrifluoroacetamide. The standard curves showed linearity over a range of 43-4269 mumol/l for GAA and 38-7325 mumol/l for creatine, which covers the range of GAA and creatine normally found in urine. The lower detection limit is 1.54 mumol/l for GAA and 1.22 mumol/l for creatine, whereas the lower quantification limit is 5.04 mumol/l for GAA and 4.19 mumol/l for creatine. This method was also employed to establish reference values for GAA and creatine in healthy infants, children and adolescents based on the analysis of 169 urine samples. Although no sex differences were observed, normal GAA urinary levels and creatine excretion are distinct in age-related subgroups. We identified a statistically significant age difference in two major groups for GAA (children under 4 years, 18-159 mumol/mmol creatinine; and subjects of 5-16 years, 18-130 mumol/mmol creatinine) whereas three groups were discriminated for creatine (children under 4 years, 0.04-1.51 mmol/mmol creatinine; subjects of 5-11 years, 0.04-1.07 mmol/mmol creatinine; and subjects of 12-16 years, 0.04-0.56 mmol/mmol creatinine). (C) 2004 Elsevier B.V. All rights reserved.