Labs Required Before Starting SGLT2 Inhibitors
The essential baseline laboratory tests before initiating SGLT2 inhibitor therapy are estimated glomerular filtration rate (eGFR) and urinalysis to assess kidney function and rule out active urinary tract infection. 1, 2
Mandatory Baseline Laboratory Assessment
Renal Function Testing
- Measure eGFR to determine eligibility and appropriate dosing, as SGLT2 inhibitors should not be initiated if eGFR is <30 mL/min/1.73 m² (though KDIGO 2020 guidelines support use down to eGFR ≥30 mL/min/1.73 m²). 1
- Check urinalysis to exclude active urinary tract infection before starting therapy, as SGLT2 inhibitors increase urinary glucose excretion, creating a favorable environment for bacterial growth. 2, 3
- Assess urinary albumin-to-creatinine ratio (U-ACR) if not recently measured, particularly in patients with diabetic kidney disease, as this helps establish baseline kidney status and monitor therapeutic response. 1
Additional Baseline Considerations
- Review current glucose levels (hemoglobin A1C or fasting glucose) to assess baseline glycemic control and determine if dose adjustments of other antihyperglycemic medications will be needed. 1
- Assess volume status clinically rather than through specific labs, but consider checking electrolytes if the patient is on diuretics or has concerns for volume depletion. 1, 2
Pre-Initiation Clinical Assessment Algorithm
Step 1: Verify Eligibility Criteria
- Confirm eGFR ≥30 mL/min/1.73 m² for initiation (some guidelines suggest ≥20 mL/min/1.73 m² may be acceptable). 1, 2
- Rule out pregnancy or breastfeeding (no lab required, clinical assessment). 1
- Exclude active urinary tract infection through urinalysis. 2
Step 2: Medication Adjustment Planning
- If patient is on insulin or sulfonylureas and meeting glycemic targets, plan to reduce insulin dose by 20% or sulfonylurea dose by 50% at initiation to prevent hypoglycemia. 1, 2
- If patient is on loop or thiazide diuretics, consider reducing diuretic dose before starting SGLT2 inhibitor to minimize volume depletion risk. 1, 2
Post-Initiation Monitoring
Early Follow-Up (First 4 Weeks)
- Monitor home glucose readings more closely during the first 4 weeks, particularly if adjusting other antihyperglycemic medications. 1
- Reassess volume status clinically and educate patients about symptoms of volume depletion (lightheadedness, orthostasis, weakness). 1, 2
- Follow up on kidney function within 2-4 weeks, as a reversible decrease in eGFR may occur and is generally not an indication to discontinue therapy. 1
Long-Term Monitoring
- Check eGFR at least every 3-6 months depending on baseline kidney function (more frequently if eGFR 30-44 mL/min/1.73 m²). 1
- Continue SGLT2 inhibitor even if eGFR falls below 30 mL/min/1.73 m² once initiated, unless not tolerated or kidney replacement therapy is started. 1
Important Caveats and Pitfalls
Common Errors to Avoid
- Do not discontinue SGLT2 inhibitors solely based on initial eGFR decline, as this represents hemodynamic adaptation and is associated with long-term kidney protection. 1, 4
- Do not overlook volume status assessment in patients on diuretics, as the combination increases risk of symptomatic hypotension and volume depletion. 1, 2
- Do not forget to educate about euglycemic diabetic ketoacidosis, which can occur even with glucose levels of 150-250 mg/dL, and instruct patients to temporarily discontinue during acute illness, prolonged fasting, or surgery. 1, 2
Special Populations
- In patients with recurrent genital mycotic infections, counsel on genital hygiene before initiation but this is not a contraindication. 1, 2
- In kidney transplant recipients, SGLT2 inhibitors have not been adequately studied and the recommendation for use does not apply to this population. 1
- In patients with history of amputation or severe peripheral arterial disease, avoid canagliflozin specifically but other SGLT2 inhibitors may be appropriate. 1