GLP-1 monitoring blood test

For follow-up

Monitoring blood test during treatment with Ozempic, Wegovy, Mounjaro, Saxenda or another GLP-1 or similar medicine. It includes glucose, glycated haemoglobin, cholesterol, kidney and liver function, electrolytes, full blood count, ferritin, vitamin D, vitamin B12, folic acid, uric acid, calcium and magnesium. It allows metabolic progress to be compared and relevant changes to be monitored during weight loss.

No prescription or appointment needed

Results in 1-2 working days

Includes: Glucose · Glycated haemoglobin · Lipid profile and ratios · Creatinine and eGFR · Sodium and potassium · AST, ALT and GGT. 16 in total. See what each one measures

What it is for

It is used to compare how glucose, cholesterol, the liver and other parameters are changing against the baseline blood test. It also allows the kidneys and electrolytes to be reviewed if there have been digestive symptoms, and micronutrients to be checked when food intake has fallen substantially.

There is no single interval that is valid for everyone. How often it is done depends on the dose, the speed of weight loss, symptoms, previous conditions and the instructions of the doctor managing the treatment.

When it is recommended

A scheduled check during treatment, as planned by the doctor
Substantial weight loss or a marked reduction in food intake
After a dose increase, if persistent vomiting or diarrhoea appears
Follow-up of a previous metabolic, liver, kidney or nutritional abnormality
Before changing or stopping treatment, if the blood test picture needs updating

Clinical comment

We do not repeat TSH or insulin automatically. TSH is measured in the baseline profile and is requested again if there is a clinical reason. Insulin and HOMA-IR are hard to compare during a treatment that acts on insulin secretion, so metabolic follow-up relies on glucose and HbA1c.

The liver and biliary profile provides a reference, but a normal blood test does not exclude gallstones. Severe pain in the upper abdomen, jaundice or persistent vomiting require medical assessment and, often, an ultrasound.

The nutritional block is included on clinical judgement, not because there is a consensus requiring it to be measured at a fixed interval in everyone. Bear in mind that symptoms set the priority: persistent vomiting with confusion, unsteadiness when walking or visual disturbances require urgent care because of the risk of thiamine deficiency and other complications.

Dr. Antonio Mas

What is tested

Glucose: Measures blood sugar at the time of the check.
Glycated haemoglobin (HbA1c): Reflects average glucose over the last two or three months and allows comparison with the previous value.
Lipid profile (total cholesterol, HDL, LDL, triglycerides) and ratios
Creatinine and eGFR: Monitor kidney function, especially if there has been vomiting, diarrhoea or dehydration.
Sodium and potassium: Identify electrolyte abnormalities related to digestive losses or insufficient intake.
AST, ALT and GGT: Enzymes that give an indication of the state of the liver.
Total bilirubin and alkaline phosphatase: Complete the liver and biliary profile.
Full blood count: Checks the blood cells and provides the platelets for FIB-4.
FIB-4 index (calculated): Estimates the probability of advanced liver fibrosis from age, transaminases and platelets.
Ferritin: Estimates iron stores, although it can also rise with inflammation or liver disease.
Vitamin D (25-OH): Assesses vitamin D stores.
Vitamin B12: Measures the circulating concentration of cobalamin.
Folic acid (folate)
Uric acid: Allows progress to be compared and adds context if there is a history of gout.
Calcium: Gives basic information about mineral metabolism.
Magnesium: Measures serum magnesium.

These tests are used to calculate Índice FIB-4. They are not separate tests.

How to prepare

Fast for 8 to 12 hours. You can drink water. Keep to your medicine schedule unless the doctor has told you otherwise. Do not bring forward or delay a dose just for the blood test.

You can add

Without another needle. It is offered when you order, so you do not have to decide now.

Thyroid functionBrings together TSH and free T4, the two basic tests for assessing how the thyroid is working.+€29.00
Sugar, insulin and inflammationAssesses insulin resistance through fasting insulin and the HOMA-IR index, plus average blood sugar over the last three months and low-grade inflammation.+€59.00

Related blood tests

We have other profiles in Obesity with more or fewer tests:

The most comprehensive is not always the most useful. If you are not sure, the one we recommend to start with is Blood test before starting GLP-1.

What it is based on

Sibal R, Balamurugan G, Langley J, et al. · Nutrients 17(23):3659
Macronutrient, Micronutrient Supplementation and Monitoring for Patients on GLP-1 Agonists: Can We Learn from Metabolic and Bariatric Surgery?
It reports that vitamin D deficiency is the most common deficiency during treatment (7.5% at six months and 13.6% at one year) and that ferritin falls markedly, and it states that there are no consensus guidelines on how often the check should be repeated. The four-month interval of this profile comes from clinical practice, not from a guideline.
European Association for the Study of the Liver, EASD y EASO · Diabetologia 67(11):2375-2392
EASL-EASD-EASO Clinical Practice Guidelines on the management of metabolic dysfunction-associated steatotic liver disease (MASLD)
It supports calculating FIB-4 as part of the check: the guideline recommends looking for liver fibrosis with a blood index in people with abdominal obesity and another metabolic factor, and that reason does not disappear because weight is being lost.

Protocol designed by Dr. Antonio Mas, specialist in Endocrinology and Nutrition, Spanish medical licence no. 080846289, and reviewed in September 2026.

This blood test is a standardised protocol and does not replace a medical consultation. If you have symptoms, a known condition or a complex clinical situation, speak to your doctor.