A MODIFICATION OF THE URINE OSMOLAL GAP - AN IMPROVED METHOD FOR ESTIMATING URINE AMMONIUM

A modification of the urine osmolal gap was evaluated as an estimate of urine [NH4]. We proposed that: (Equation Present) 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 [NH+4] were compared with measured urine [NH+4]. There was a significant positive linear correlation between the urine [NH+4] and the modified urine osmolal gap in normal volunteers (r = 0.81; p < 0.01) and in individuals with ketonuria (r = 0.93; p < 0.001). The originally described urine osmolal gap greatly overestimated the urine [NH+4] but also showed a significant correlation. The urine anion gap was not a valid estimate of urine [NH+4] within the range of values measured in our subjects. The modified urine osmolal gap is an improvement over previously described estimates of urine [NH+4] and can be used as a single calculation in place of the other two. © 1990 S. Karger AG, Basel.