Medline ® Abstract for Reference 11
of 'Urine anion and osmolal gaps in metabolic acidosis'
A modification of the urine osmolal gap: an improved method for estimating urine ammonium.
Dyck RF, Asthana S, Kalra J, West ML, Massey KL
Am J Nephrol. 1990;10(5):359-62.
A modification of the urine osmolal gap was evaluated as an estimate of urine [NH4+]. We proposed that: Urine [NH4+]= Urine osmolality - [2(Na+ + K+) + urea + glucose]/2 Spot urine samples were collected from normal volunteers and from individuals with ketonuria; the modified urine osmolal gap as well as two other previously described estimates of urine [NH4+]were compared with measured urine [NH4+]. There was a significant positive linear correlation between the urine [NH4+]and the modified urine osmolal gap in normal volunteers (r = 0.81; p less than 0.01) and in individuals with ketonuria (r = 0.93; p less than 0.001). The originally described urine osmolal gap greatly overestimated the urine [NH4+]but also showed a significant correlation. The urine anion gap was not a valid estimate of urine [NH4+]within the range of values measured in our subjects. The modified urine osmolal gap is an improvement over previously described estimates of urine [NH4+]and can be used as a single calculation in place of the other two.
Department of Medicine, University of Saskatchewan, Saskatoon, Canada.