Post hoc analysis reports lower albuminuria on tirzepatide in the SURMOUNT obesity trials

A post hoc analysis of the SURMOUNT-1 and SURMOUNT-2 obesity trials found that tirzepatide, the drug sold as Zepbound and Mounjaro, was linked to lower levels of albumin in the urine, a marker doctors use to track early kidney damage. Kidney filtration did not get worse in either trial ^[1].

The analysis pooled all tirzepatide dose groups in each trial and compared them with placebo. SURMOUNT-1 enrolled 2,539 people with overweight or obesity but no type 2 diabetes, tested at doses of 5, 10, and 15 mg. SURMOUNT-2 enrolled 938 people with obesity and type 2 diabetes, tested at 10 and 15 mg ^[1].

The measurement at the center of the analysis is the urine albumin-to-creatinine ratio, or UACR, a standard test for kidney stress. At the start of the trials, median UACR was low in both groups: 6.0 mg/g in SURMOUNT-1 and 13.0 mg/g in SURMOUNT-2, reflecting that most participants did not have significant kidney damage to begin with ^[1].

By week 72, UACR had fallen more on tirzepatide than on placebo in both trials. The estimated difference was 8.4% in SURMOUNT-1 and 31.1% in SURMOUNT-2 ^[1]. Among participants who started with elevated albuminuria — a UACR of 30 mg/g or higher, a level associated with higher kidney risk — the effect was much larger: a 42.3% placebo-corrected reduction in SURMOUNT-1 and a 55.2% reduction in SURMOUNT-2 ^[1].

Kidney filtration, measured by estimated glomerular filtration rate (eGFR), did not decline on tirzepatide. In SURMOUNT-1, tirzepatide was linked to a small increase in eGFR compared with placebo when measured using cystatin-C-based methods, by 3.2 mL/min per 1.73 m² for one equation and 1.9 mL/min per 1.73 m² for another ^[1]. In SURMOUNT-2, eGFR rose in both the tirzepatide and placebo groups, with no meaningful difference between them ^[1]. The researchers concluded that tirzepatide was associated with reduced albuminuria without any adverse change in eGFR ^[1].

Why it matters for patients

Albuminuria is an early warning sign that the kidneys' filtering units are under stress, often years before more serious kidney disease develops. It's tracked closely in people with obesity and type 2 diabetes because both conditions raise the risk of chronic kidney disease over time ^[1].

This analysis suggests tirzepatide may lower that stress signal, and the effect looks larger in people whose kidneys were already showing more strain at the start. That is a different question from asking whether the drug prevents kidney failure or dialysis, which this analysis does not address. It is a post hoc analysis — meaning researchers looked back at kidney data collected during trials that were designed to test weight loss and diabetes control, not kidney outcomes specifically ^[1].

The finding that filtration did not worsen, and even improved slightly on some measures in SURMOUNT-1, is reassuring for a drug that causes substantial weight loss, since sudden weight change can sometimes affect kidney measurements. Still, this is one analysis from two trials, and the source material does not report how these findings compare with other GLP-1 or dual-agonist drugs, or with long-term kidney outcomes beyond 72 weeks.

What happens next

The source material does not describe planned follow-up studies specifically on tirzepatide and kidney outcomes. Related work is underway: a separate trial called TRANSCEND-CKD is testing retatrutide, a different drug, specifically in people with chronic kidney disease, according to research citing this same analysis ^[1]. Whether tirzepatide itself will be studied in a dedicated kidney-outcomes trial is not stated in the available sources.