Does glucosuria in a urinalysis 40 minutes after a glucose tolerance test (GTT) indicate any concerns in a pregnant woman at 26 weeks gestation?

From the Guidelines

Glucosuria detected during a routine urinalysis performed 40 minutes after a glucose load for a glucose tolerance test in a pregnant woman at 26 weeks is not concerning and should not be interpreted as abnormal. This finding is expected and represents a normal physiological response to the high glucose load that was administered for the test, as noted in the guidelines for laboratory analysis in the diagnosis and management of diabetes mellitus 1. During pregnancy, the renal threshold for glucose excretion is often lower than in non-pregnant individuals, and after consuming a concentrated glucose solution (typically 50-75g), blood glucose levels rise significantly, causing temporary spillage of glucose into the urine.

The diagnosis of gestational diabetes should be based solely on the blood glucose measurements taken during the test, not on the urinalysis results, according to the standards of medical care in diabetes 1. If the blood glucose values from the glucose tolerance test are within normal limits, the presence of glucose in the urine sample collected during the test can be disregarded. However, persistent glucosuria found on routine prenatal visits (when not following a glucose load) would warrant further investigation. The American Diabetes Association (ADA) recommends that all pregnant women not previously known to have diabetes should be evaluated for gestational diabetes mellitus (GDM) at 24 to 28 weeks of gestation, using either the one-step or two-step protocol, depending on regional preferences 1.

Key points to consider:

• The one-step approach involves a 75-g oral glucose tolerance test (OGTT) with plasma glucose measurement fasting and at 1 and 2 hours 1.
• The two-step approach involves a 50-g glucose challenge test, followed by a 100-g OGTT if the initial test is abnormal 1.
• The diagnosis of GDM is made when any of the plasma glucose values exceed the specified thresholds, which vary depending on the approach used 1.
• The presence of glucosuria during the glucose tolerance test does not affect the diagnosis of GDM, which should be based solely on blood glucose measurements.

From the Research

Glucosuria in Urinalysis

• Glucosuria, or the presence of glucose in the urine, can be an indicator of gestational diabetes mellitus (GDM) during pregnancy 2.
• However, studies have shown that glucosuria after an oral glucose challenge is a poor predictor of GDM, pre-eclampsia, and newborn size at birth, and therefore has limited clinical benefit 3.
• The sensitivity of glycosuria as a screening test for GDM is low, ranging from 8.2% to 27% in different studies 3, 4.

Clinical Value of Glycosuria

• Glycosuria is more pronounced in women with lower height and body weight, who presumably have a smaller plasma distribution volume 3.
• Severe glycosuria, although increased in women with GDM, occurs in only 18% of cases and is not a reliable indicator of GDM 4.
• Detection of severe glycosuria before 24 weeks' gestation may be an indication to perform earlier blood glucose screening, but routine screening for glycosuria at each prenatal visit does not appear to be clinically useful 4.

Diagnosis of Gestational Diabetes

• The diagnosis of GDM is typically made using a 75-g oral glucose tolerance test (OGTT) or a 100-g OGTT, with criteria derived from the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study 2, 5.
• The OGTT is a more reliable test for diagnosing GDM than glycosuria, and its results should be interpreted with caution, taking into account factors such as specimen handling and preanalytical glycolysis 5.