Ketonuria is Associated with a Positive 1-Hour Oral Glucose Tolerance Test

Evidence suggests that fasting prior to the 1-hour oral glucose tolerance test (OGTT) may increase the probability of a positive screen result. Because ketonuria may be a surrogate marker for prolonged fasting, we examined the association between ketonuria and a positive OGTT screen. This is a secondary analysis of a single-center prospective randomized trial comparing the effects of a prolonged fast for 6 or more hours versus eating within 2 hours of the 1-hr OGTT. A positive screen was defined as a glucose ≥140 mg/dL. Ketonuria data were collected for participants enrolled in the trial when their obstetrics visit coincided with the OGTT. Rates of ketonuria in the fasting versus the fed group were ascertained. Fisher’s exact test was then used to analyze ketonuria and the rate of a screen positive result. Secondarily, we analyzed mean glucose values in those with and without ketonuria. We then calculated mean glucose values based on the ketonuria level (none, trace, 1+, 2+/3+) followed by the mean fasting times prior to the OGTT based on these levels of ketonuria. Of 200 participants, 195 completed the 1-hour OGTT after 24 weeks gestation. Urine ketone levels were available in 168 patients, with an OGTT screen positive rate of 28.2% (n=37). 20 participants (11.9%) had evidence of ketonuria. Among those with ketonuria, the screen positive rate was 50.0% (n=10), compared to 18.2% (n=27) in those without ketonuria (p-value = 0.003). The mean glucose value in the ketonuria group was 154.4 mg/dL versus 115.7 mg/dL in those without (p-value = < 0.001). In participants with ketonuria, mean glucose values remained relatively similar and were not dependent on the level of ketones present (153-155 mg/dL) (Table 2). However, the ketonuria level was associated with the length of fasting prior to the OGTT ranging from 5.7 hours in those without ketonuria to 10.0 hours in those with 2+/3+ ketonuria (Table 2). Patients with ketonuria at the time of the 1-hr OGTT had higher mean glucose levels and were more likely to screen positive than those without evidence of ketonuria.View Large Image Figure ViewerDownload Hi-res image Download (PPT)