Primary care physicians (PCPs) are on the front lines of obesity care as more patients use GLP-1 receptor agonists and related medications. These treatments can be highly effective, but safe care involves more than just tracking weight. Routine lab work helps establish a baseline, monitor metabolic and organ health, catch problems early, and show health factors beyond just the scale.

Establishing Baseline Metrics and Routine Monitoring 

Before prescribing an antiobesity medication, clinicians need a clear baseline. Initial testing should include A1c and fasting glucose, creatinine and estimated glomerular filtration rate (eGFR), liver enzymes, and a lipid profile. For patients with hypertension or type 2 diabetes, the American Diabetes Association also recommends a urine albumin-to-creatinine ratio to help detect early kidney stress.

"When starting a GLP-1 receptor agonist, it's important to establish a comprehensive baseline rather than focusing only on glycemic measures," said Imad Aziz, MD, a family medicine physician with Advocate Health Care in South Elgin, Illinois. "For patients who are stable on therapy and doing well clinically, A1c is typically monitored every 3-6 months, while comprehensive metabolic testing can be repeated every 6-12 months."

Follow-up should reflect each patient's risk, with more frequent glucose and kidney checks when clinically warranted.

"There is no standard recommendation or guideline for lab work for all patients treated with a GLP-1 agonist medication," explained Lisa Netkowicz, MD, family medicine physician and medical bariatrician, UW Health, and clinical assistant professor of family medicine and community health, UW School of Medicine and Public Health in Madison, Wisconsin. "Prior to starting a GLP-1 agonist medication, all patients should have labs to assess kidney function, liver function, blood sugars, and blood lipids."

Body composition testing can add context during rapid weight loss. DEXA or bioelectrical impedance analysis can distinguish fat loss from muscle loss, especially in older adults and patients at risk for frailty.

"DEXA can be used at baseline and periodically during GLP-1–based weight treatment to distinguish fat-mass loss from lean-mass loss, rather than relying on scale weight alone," noted Yuval Pinto, MD, assistant professor of medicine and part of the healthful eating, activity, and weight program at Johns Hopkins University School of Medicine in Baltimore. "It is most useful when results would change management — such as in older adults, sarcopenia/frailty risk, rapid weight loss, low protein intake, or unexpectedly poor strength/function."

Mitigating Dehydration Risks and Renal Complications 

Nausea, vomiting, diarrhea, and slower digestion are common with these medications. Although GLP-1 drugs rarely harm the kidneys directly, dehydration can reduce kidney blood flow and trigger acute kidney injury, particularly when treatment starts or the dose increases, according to June 2026 clinical data.

"Monitoring kidney function is the priority for surveillance because the main mechanism of GLP-1 agonist-associated acute kidney injury is dehydration from nausea, vomiting, and diarrhea and not direct nephrotoxicity," said Netkowicz.

Closer follow-up is especially important for patients at higher risk of dehydration, including older adults, those with chronic kidney disease, and those taking diuretics, nonsteroidal anti-inflammatory drugs, or renin-angiotensin-aldosterone system inhibitors.

"Most renal complications associated with GLP-1 receptor agonists are related to dehydration from significant nausea, vomiting, or diarrhea rather than a direct effect of the medication itself," said Aziz. "In higher-risk populations, including older adults, patients with chronic kidney disease, those taking diuretics, or individuals experiencing recurrent gastrointestinal side effects, I recommend checking serum creatinine and eGFR shortly after treatment initiation or dose escalation and repeating testing when clinically indicated."

When dehydration is avoided, GLP-1 therapy may also improve kidney and liver markers.

"AKI signal is a volume-depletion problem concentrated in titration, in patients with reduced baseline eGFR, and in those on drugs that blunt renal autoregulation," said Pinto. "Monitoring should therefore be risk-stratified and event-triggered, not calendar-based."

Evaluating Weight–Loss Plateaus and Secondary Causes 

Weight-loss plateaus are common in long-term obesity care. Rather than assuming nonadherence, review labs, medications, sleep, nutrition, and activity for factors that may be slowing progress.

"Weight-loss plateaus are common and should be viewed as a normal part of the treatment journey rather than an automatic sign of treatment failure," said Aziz. "Before attributing a plateau to nonadherence, I recommend evaluating for potentially reversible contributors such as hypothyroidism, worsening glycemic control, medication-related weight gain, sleep disorders, or other metabolic conditions that may affect weight regulation."

For a persistent plateau, consider thyroid, A1c, metabolic, liver, blood count, and — when appropriate — cortisol testing. Also review medications that can promote weight gain, including beta-blockers, antihistamines, steroids, insulin, sulfonylureas, and some psychiatric drugs.

Translating Biomarkers Into Patient Wellness Goals 

Lab trends can shift the conversation from weight alone to overall health.

"The most useful wellness markers are those that improve rapidly and independently of the number on the scale which include A1c and fasting glucose, atherogenic lipids, blood pressure, urine albumin-to-creatinine ratio, liver enzymes, and high-sensitivity CRP," Netkowicz said. "Framing progress around these lab evaluations gives patients concrete evidence that GLP-1 therapy is protecting their heart, kidneys, and liver even during an inevitable weight plateau, which is exactly the moment adherence is most fragile."

Reviewing those trends during visits turns lab results into meaningful milestones and supports shared decision-making.

"One of the most effective ways to keep patients engaged is to help them recognize that improvements in health often occur before they are fully reflected on the scale," explained Aziz. "Rather than focusing exclusively on a period of slowed weight loss, I try to emphasize the broader health benefits that are occurring."

Lab work is also useful for patients who cannot or prefer not to use GLP-1 medications. Making it routine helps PCPs deliver safer, more personalized care and show progress beyond the scale.

The experts cited in this article had no relevant disclosures.