Time in Range Linked to Lower Kidney Damage Risk in Type 2 Diabetes: A Retrospective Study of Inpatients
Type 2 diabetes (T2DM) affects over 537 million people worldwide, and one of its most dangerous complications—diabetic kidney disease—silently damages kidneys before symptoms appear. Now, new research highlights a simple metric that could help predict and prevent this damage: time in range (TIR), the percentage of time blood glucose stays within a healthy target range.
A team of researchers from Peking University International Hospital, Beijing Friendship Hospital, and Peking University People’s Hospital analyzed data from 1014 T2DM inpatients to explore how TIR relates to urinary albumin excretion rate (UAER), a key marker of kidney health. Their findings, published in the Chinese Medical Journal in 2022, offer fresh insights into how glucose control impacts kidney function.
What Is TIR—and Why Does It Matter?
TIR measures how much time a person’s blood glucose stays between 3.9–10.0 mmol/L (the target range recommended for most T2DM patients). Unlike HbA1c (the “gold standard” for long-term glucose control), TIR captures daily fluctuations—like spikes after meals or dips during sleep—that HbA1c misses.
Glycemic variability (changes in blood glucose levels) is linked to diabetic microvascular complications, including kidney disease. TIR fills this gap by showing whether treatments are reducing dangerous highs or lows over time.
How the Study Worked
The retrospective study included T2DM patients aged 18+ with a stable glucose-lowering regimen for 3 months. Researchers excluded those with severe complications (e.g., diabetic ketoacidosis, heart failure) or incomplete data.
For 3 consecutive days, patients had 6 daily fingerstick glucose tests (at midnight, 3 AM, fasting, and after each meal). TIR was calculated as the percentage of readings in the 3.9–10.0 mmol/L range.
To measure UAER (a sign of kidney damage), patients collected urine for 3 days. UAER was classified as:
- Normal: <30 mg/g (no kidney damage)
- Microalbuminuria: 30–300 mg/g (early kidney damage)
- Macroalbuminuria: >300 mg/g (advanced kidney damage)
Key Findings: TIR and Kidney Health Are Closely Linked
The results were clear: lower TIR correlated with more severe kidney damage. Here’s what the data showed:
- Patients with normal UAER had an average TIR of 70%.
- Those with microalbuminuria (early kidney damage) had a TIR of 50%.
- Those with macroalbuminuria (advanced damage) had a TIR of just 30%.
When patients were split into TIR quartiles (four groups based on TIR levels), the trend was even starker:
- Lowest TIR (Q1: <55%): 41% had microalbuminuria, 24% had macroalbuminuria.
- Highest TIR (Q4: >83%): Only 5.5% had microalbuminuria, and 0% had macroalbuminuria.
Even after adjusting for factors like age, BMI, diabetes duration, HbA1c, and blood pressure, TIR remained a strong predictor of kidney damage. For every 10% increase in TIR, the odds of microalbuminuria dropped by 42% and macroalbuminuria by 74%.
Why TIR Matters More Than HbA1c Alone
HbA1c measures average glucose over 2–3 months, but it doesn’t show how often glucose spikes or drops. For example, two people with the same HbA1c could have very different daily glucose patterns: one might spend most of the day in range, while the other has frequent highs and lows.
This study adds to growing evidence that TIR is a better marker for microvascular complications (like kidney or eye damage) than HbA1c alone. The Diabetes Control and Complications Trial—a landmark study on type 1 diabetes—found that every 10% drop in TIR increased the risk of microalbuminuria by 40%. This new research extends that link to T2DM.
What This Means for People with T2DM
For patients and caregivers, the takeaway is simple: tracking TIR can help catch kidney damage early. While continuous glucose monitoring (CGM) is the most accurate way to measure TIR, even regular fingerstick tests (like the 6-per-day schedule used in the study) can provide valuable insights.
The study also highlights the need to look beyond HbA1c. If two patients have the same HbA1c but different TIRs, the one with lower TIR may face a higher risk of kidney disease—even if their “average” glucose looks healthy.
Limitations to Consider
The study has a few caveats:
- Cohort Restriction: All participants were Chinese inpatients, so results may not apply to other ethnic groups.
- Hospital Environment: Patients followed a hospital diet, which may not reflect real-world eating habits.
- Glucose Monitoring: Fingerstick tests were limited to 6 times a day (missing some overnight fluctuations), unlike CGM which tracks glucose 24/7.
Conclusion
This research reinforces that time in range is a critical metric for managing type 2 diabetes—especially when it comes to protecting kidney health. For patients, working with doctors to increase TIR (by adjusting diet, exercise, or medications) could lower the risk of diabetic kidney disease, a leading cause of end-stage renal failure.
For clinicians, TIR offers a more complete picture of glucose control than HbA1c alone. By prioritizing TIR, healthcare teams can intervene earlier to prevent irreversible kidney damage.
Original Study Citation:
Chai S, Wu S, Xin S, Yuan N, Sun J, Zhang X, Ji LN. Negative association of time in range and urinary albumin excretion rate in patients with type 2 diabetes mellitus: a retrospective study of inpatients. Chinese Medical Journal 2022;135:1052–1056. doi:10.1097/CM9.0000000000001914
Full study available at: doi.org/10.1097/CM9.0000000000001914
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