Before starting Mounjaro (tirzepatide) for type 2 diabetes, blood tests are essential to ensure safe and effective treatment. These investigations establish baseline health parameters, confirm your diabetes diagnosis, and identify any conditions requiring special monitoring. Blood tests assess glycaemic control through HbA1c measurement, evaluate kidney and liver function, and screen for cardiovascular risk factors. Your GP or diabetes specialist will review all results to determine whether Mounjaro is appropriate for your individual circumstances and to establish a monitoring plan throughout your treatment journey.
Quick Answer: Blood tests before Mounjaro assess baseline diabetes control (HbA1c), kidney function (eGFR, creatinine), liver health (LFTs), and cardiovascular risk (lipid profile) to ensure safe prescribing and establish monitoring parameters.
Mounjaro (tirzepatide) is a glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist licensed in the UK for the treatment of type 2 diabetes mellitus. Before initiating treatment with Mounjaro, blood testing is essential to establish baseline health parameters and identify any conditions requiring special monitoring.
Blood tests serve multiple purposes in the pre-treatment assessment. Firstly, they confirm the diagnosis of type 2 diabetes and assess the degree of glycaemic control through HbA1c measurement. This baseline value is crucial for monitoring treatment efficacy over subsequent months. Secondly, blood tests evaluate kidney and liver function, as these organs are important in the context of diabetes management and potential adverse effects.
Additionally, baseline investigations help identify co-existing conditions that may influence treatment decisions. While animal studies have shown an association between GLP-1 receptor agonists and thyroid C-cell tumours, there is no established link in humans, and routine thyroid function testing is not specifically required for tirzepatide initiation according to the UK SmPC. Lipid profiles provide valuable information about cardiovascular risk factors, which is relevant given that many patients with type 2 diabetes have dyslipidaemia.
Your GP or diabetes specialist will review all blood test results before prescribing Mounjaro, ensuring the medication is appropriate for your individual circumstances and that any necessary precautions are in place. Particular attention should be paid to a history of pancreatitis or gallbladder disease, as these are specific cautions mentioned in the Mounjaro SmPC.
A panel of blood tests is typically required before commencing Mounjaro therapy. The specific investigations may vary slightly depending on individual patient factors, but the following tests form the core pre-treatment assessment:
HbA1c (Glycated Haemoglobin): This test measures average blood glucose levels over the preceding 8–12 weeks and is the gold standard for assessing glycaemic control. NICE recommends Mounjaro as a treatment option when HbA1c remains elevated despite other interventions. A baseline HbA1c provides a reference point for evaluating treatment response.
Renal Function Tests: These include serum creatinine, estimated glomerular filtration rate (eGFR), and urea. According to the Mounjaro SmPC, no dose adjustment is required based on renal function, including in patients with severe renal impairment or end-stage renal disease. However, monitoring renal function is advised if severe gastrointestinal adverse effects or volume depletion occur.
Urine Albumin:Creatinine Ratio (UACR): This test assesses for diabetic kidney disease and is a standard part of diabetes care as recommended in NICE NG28.
Liver Function Tests (LFTs): Alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and bilirubin may be measured to assess hepatic health. According to the SmPC, no dose adjustment is required for patients with hepatic impairment.
Lipid Profile: Total cholesterol, HDL cholesterol, non-HDL cholesterol, and triglycerides are measured to assess cardiovascular risk in line with NICE NG238 guidance.
If you are taking insulin or sulphonylureas, your doctor will review these medications as dose adjustments may be needed when starting Mounjaro to reduce the risk of hypoglycaemia. For women of childbearing potential, pregnancy testing and contraception advice may be provided, as Mounjaro is not recommended during pregnancy.
Interpreting blood test results requires clinical expertise, and your GP or diabetes specialist will discuss the findings with you. However, understanding the key parameters can help you engage more effectively in treatment decisions.
HbA1c levels are reported as millimoles per mole (mmol/mol) in the UK. A diagnosis of type 2 diabetes is typically made when HbA1c is ≥48 mmol/mol (6.5%). NICE guidance (NG28) suggests considering intensification of therapy when HbA1c remains above individualised targets despite current treatment. For many patients, the target is around 48-53 mmol/mol (6.5-7.0%), though this may be adjusted based on individual circumstances, including age, comorbidities, and hypoglycaemia risk.
Renal function is primarily assessed through eGFR, which estimates how efficiently the kidneys filter waste. Normal eGFR is >90 mL/min/1.73m². Values between 60–89 indicate mild reduction, 30–59 moderate reduction, and <30 severe reduction in kidney function. Your clinician will consider renal function when determining appropriate diabetes management.
Liver function tests have established reference ranges, though these may vary slightly between laboratories. Elevated transaminases (ALT, AST) may indicate liver inflammation or damage, whilst raised ALP or bilirubin can suggest biliary obstruction or other hepatic conditions. Mild elevations are common in patients with type 2 diabetes due to non-alcoholic fatty liver disease.
Lipid results are interpreted in the context of cardiovascular risk. Current NICE guidance (NG238) recommends using risk calculators such as QRISK3 to guide lipid management. For those at increased cardiovascular risk, the aim is typically to achieve at least a 40% reduction in non-HDL cholesterol with appropriate statin therapy, rather than targeting specific threshold values.
If any results are outside normal ranges, your healthcare provider will explain the implications and whether this affects your suitability for Mounjaro treatment. In some cases, abnormal results may require further investigation or optimisation before starting the medication.
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Start HereOnce Mounjaro treatment is initiated, regular blood test monitoring is essential to assess treatment efficacy, detect adverse effects, and adjust therapy as needed. The frequency and type of monitoring will be individualised based on your clinical response and any emerging concerns.
HbA1c monitoring is typically performed every 3–6 months during the first year of treatment, then at least annually once glycaemic control is stable. NICE recommends reviewing treatment if HbA1c targets are not achieved within 6 months. Significant improvements in HbA1c are usually observed within 12–24 weeks of starting Mounjaro.
Renal function tests should be repeated at least annually, or more frequently if baseline kidney function is impaired or if you develop symptoms suggesting renal deterioration. The Mounjaro SmPC advises monitoring renal function in patients who experience severe gastrointestinal adverse reactions or dehydration.
Liver function tests may be repeated based on clinical indications rather than as routine tirzepatide-specific monitoring. If you develop symptoms such as persistent nausea, vomiting, abdominal pain, dark urine, or jaundice, contact your GP promptly for urgent assessment.
Lipid profiles are typically rechecked annually as part of standard diabetes care.
Diabetic retinopathy screening: If you have pre-existing diabetic retinopathy, particularly if you are also on insulin, you should be monitored for potential worsening when HbA1c levels fall rapidly, as noted in the Mounjaro SmPC.
When to seek medical advice: Contact your GP if you experience:
Severe or persistent gastrointestinal symptoms (nausea, vomiting, diarrhoea, abdominal pain)
Signs of pancreatitis (severe upper abdominal pain radiating to the back)
Symptoms of gallbladder disease (right upper quadrant pain, fever, jaundice)
Signs of hypoglycaemia (if taking Mounjaro with insulin or sulphonylureas)
Symptoms of dehydration (dizziness, reduced urination)
Your healthcare team will provide specific guidance on monitoring schedules and warning signs tailored to your individual circumstances, ensuring safe and effective long-term treatment with Mounjaro.
Essential blood tests include HbA1c to assess diabetes control, renal function tests (eGFR and creatinine), liver function tests, lipid profile, and urine albumin:creatinine ratio. Your GP will review all results before prescribing Mounjaro to ensure the medication is safe and appropriate for you.
HbA1c is typically monitored every 3–6 months during the first year, then annually once stable. Renal function and lipid profiles are usually checked at least annually, with more frequent monitoring if you have existing kidney impairment or develop concerning symptoms.
According to the UK SmPC, no dose adjustment is required for Mounjaro based on renal function, including in severe renal impairment. However, your doctor will monitor kidney function closely, particularly if you experience gastrointestinal side effects or dehydration.
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