B Lee1, G A Diaz2, W Rhead3, U Lichter-Konecki4, A Feigenbaum5, S A Berry6, C Le Mons7, J Bartley8, N Longo9, S C Nagamani10, W Berquist11, R C Gallagher12, C O Harding13, S E McCandless14, W Smith15, A Schulze16, M Marino13, R Rowell17, D F Coakley18, M Mokhtarani18, B F Scharschmidt18. 1. Baylor College of Medicine, Houston, TX, USA. Electronic address: blee@bcm.edu. 2. Icahn School of Medicine at Mount Sinai, New York, NY, USA. 3. The Medical College of Wisconsin, Milwaukee, WI, USA. 4. Drexel University College of Medicine, Philadelphia, PA, USA. 5. Univ. of CA, San Diego, CA, USA. 6. Univ. of Minnesota, Minneapolis, MN, USA. 7. National Urea Cycle Disorders Foundation, Pasadena, CA, USA. 8. Miller Children's Hospital, Long Beach, CA, USA. 9. Univ. of UT, Salt Lake City, UT, USA. 10. Baylor College of Medicine, Houston, TX, USA. 11. Stanford Univ., Palo Alto, CA, USA. 12. Univ. of CA, San Francisco, USA. 13. Oregon Health Sciences, Portland, OR, USA. 14. Case Western Reserve Univ. Medical Center, Cleveland, OH, USA. 15. Maine Medical Ctr., Portland, ME, USA. 16. The Hospital for Sick Children, Univ. of Toronto, Canada. 17. MED Technical Consulting, Inc., Union City, CA, USA. 18. Horizon Therapeutics, Brisbane, CA, USA.
Abstract
UNLABELLED: Blood ammonia and glutamine levels are used as biomarkers of control in patients with urea cycle disorders (UCDs). This study was undertaken to evaluate glutamine variability and utility as a predictor of hyperammonemic crises (HACs) in UCD patients. METHODS: The relationships between glutamine and ammonia levels and the incidence and timing of HACs were evaluated in over 100 adult and pediatric UCD patients who participated in clinical trials of glycerol phenylbutyrate. RESULTS: The median (range) intra-subject 24-hour coefficient of variation for glutamine was 15% (8-29%) as compared with 56% (28%-154%) for ammonia, and the correlation coefficient between glutamine and concurrent ammonia levels varied from 0.17 to 0.29. Patients with baseline (fasting) glutamine values >900 μmol/L had higher baseline ammonia levels (mean [SD]: 39.6 [26.2]μmol/L) than patients with baseline glutamine ≤ 900 μmol/L (26.6 [18.0]μmol/L). Glutamine values >900 μmol/L during the study were associated with an approximately 2-fold higher HAC risk (odds ratio [OR]=1.98; p=0.173). However, glutamine lost predictive significance (OR=1.47; p=0.439) when concomitant ammonia was taken into account, whereas the predictive value of baseline ammonia ≥ 1.0 upper limit of normal (ULN) was highly statistically significant (OR=4.96; p=0.013). There was no significant effect of glutamine >900 μmol/L on time to first HAC crisis (hazard ratio [HR]=1.14; p=0.813), but there was a significant effect of baseline ammonia ≥ 1.0 ULN (HR=4.62; p=0.0011). CONCLUSIONS: The findings in this UCD population suggest that glutamine is a weaker predictor of HACs than ammonia and that the utility of the predictive value of glutamine will need to take into account concurrent ammonia levels.
UNLABELLED: Blood ammonia and glutamine levels are used as biomarkers of control in patients with urea cycle disorders (UCDs). This study was undertaken to evaluate glutamine variability and utility as a predictor of hyperammonemic crises (HACs) in UCD patients. METHODS: The relationships between glutamine and ammonia levels and the incidence and timing of HACs were evaluated in over 100 adult and pediatric UCD patients who participated in clinical trials of glycerol phenylbutyrate. RESULTS: The median (range) intra-subject 24-hour coefficient of variation for glutamine was 15% (8-29%) as compared with 56% (28%-154%) for ammonia, and the correlation coefficient between glutamine and concurrent ammonia levels varied from 0.17 to 0.29. Patients with baseline (fasting) glutamine values >900 μmol/L had higher baseline ammonia levels (mean [SD]: 39.6 [26.2]μmol/L) than patients with baseline glutamine ≤ 900 μmol/L (26.6 [18.0]μmol/L). Glutamine values >900 μmol/L during the study were associated with an approximately 2-fold higher HAC risk (odds ratio [OR]=1.98; p=0.173). However, glutamine lost predictive significance (OR=1.47; p=0.439) when concomitant ammonia was taken into account, whereas the predictive value of baseline ammonia ≥ 1.0 upper limit of normal (ULN) was highly statistically significant (OR=4.96; p=0.013). There was no significant effect of glutamine >900 μmol/L on time to first HAC crisis (hazard ratio [HR]=1.14; p=0.813), but there was a significant effect of baseline ammonia ≥ 1.0 ULN (HR=4.62; p=0.0011). CONCLUSIONS: The findings in this UCD population suggest that glutamine is a weaker predictor of HACs than ammonia and that the utility of the predictive value of glutamine will need to take into account concurrent ammonia levels.
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