Glucosuria with Normal Renal Function and HbA1c 5.7%
This patient most likely has renal glucosuria (familial renal glycosuria), a benign condition caused by reduced renal glucose reabsorption threshold, and requires no treatment beyond confirming the diagnosis and ruling out diabetes.
Diagnostic Approach
The key diagnostic step is to confirm that glucosuria persists despite normal blood glucose levels. This patient's HbA1c of 5.7% falls in the prediabetes range (5.7-6.4%), but with normal renal function, this level should not cause glucosuria 1. The presence of glucose in urine with normal glycemic control suggests a primary renal tubular defect rather than diabetes.
Confirm the Diagnosis
- Measure fasting plasma glucose and perform an oral glucose tolerance test to definitively exclude diabetes, as HbA1c alone may not capture all cases of dysglycemia 1, 2.
- Obtain simultaneous blood glucose and urine glucose measurements to document glucosuria occurring at normal blood glucose levels (typically <180 mg/dL, the normal renal threshold) 3.
- Verify normal renal function with eGFR calculation and ensure no proteinuria or other signs of kidney disease are present 1.
Rule Out Secondary Causes
- Screen for medications that can cause glucosuria, particularly SGLT2 inhibitors (dapagliflozin, empagliflozin), which intentionally promote renal glucose excretion 3.
- Assess for pregnancy, as pregnancy can lower the renal glucose threshold and cause benign glucosuria.
- Exclude Fanconi syndrome by checking for other tubular defects (phosphaturia, aminoaciduria, bicarbonate wasting) if there are additional clinical concerns.
Management Strategy
No treatment is required for isolated renal glucosuria once diabetes is excluded. This is a benign condition that does not progress to kidney disease or diabetes 3.
Address the Prediabetes
While the glucosuria itself requires no intervention, the HbA1c of 5.7% indicates prediabetes and warrants lifestyle modification 1, 4:
- Implement dietary changes including sodium restriction to <2g/day, increased vegetables, fruits, whole grains, fiber, legumes, plant-based proteins, and unsaturated fats while limiting processed meats, refined carbohydrates, and sweetened beverages 1, 4.
- Prescribe moderate-intensity physical activity for at least 150 minutes per week to reduce progression to diabetes 1, 4.
- Target weight loss if BMI >25 kg/m² and achieve smoking cessation if applicable 4.
- Consider metformin if lifestyle modifications fail to reduce HbA1c below 5.7% after 3-6 months, particularly if the patient has additional risk factors like obesity or family history of diabetes 4.
Monitoring Plan
- Recheck HbA1c every 3-6 months to monitor for progression to diabetes, as prediabetes increases risk 1, 4.
- Annual screening for albuminuria is warranted, as even prediabetes (HbA1c 5.7-6.4%) is associated with increased urinary albumin excretion and early kidney damage 5, 6.
- No specific monitoring of glucosuria is needed once the diagnosis of benign renal glucosuria is established.
Critical Pitfalls to Avoid
- Do not assume glucosuria equals diabetes without confirming elevated blood glucose levels, as renal glucosuria can occur with completely normal glucose metabolism 3.
- Do not overlook the prediabetes diagnosis (HbA1c 5.7%) simply because the glucosuria is benign—this patient still requires diabetes prevention interventions 4, 5.
- Do not initiate SGLT2 inhibitors for the prediabetes in this patient, as these drugs would worsen the glucosuria and are not indicated for prediabetes without established cardiovascular or kidney disease 4, 3.
- Do not dismiss the need for albuminuria screening even though renal function is normal, as prediabetes with HbA1c ≥5.7% is independently associated with increased UACR and early microvascular damage 6.
- Do not misinterpret HbA1c in the context of kidney disease if renal function later declines, as CKD can falsely elevate or lower HbA1c depending on anemia, uremia, and erythropoietin use 1, 7.