Essential Blood Tests for Tenofovir Users

When taking tenofovir, a medication used in the management of HIV-1 pre-exposure prophylaxis (PrEP) and chronic hepatitis B, monitoring certain blood tests is crucial. These tests help ensure the medication is working effectively and safely, and they can detect potential side effects early. This guide outlines the key blood tests you should be aware of while on tenofovir.

What is Tenofovir?

Tenofovir disoproxil fumarate is an antiviral medication used for two main purposes: as part of a combination therapy for HIV-1 pre-exposure prophylaxis (PrEP) and for treating chronic hepatitis B. For those using tenofovir as PrEP, it is often combined with another medication called emtricitabine (Truvada). For hepatitis B, tenofovir is used alone or alongside other treatments. It is important to monitor certain health markers to ensure the drug's safety and efficacy.

Key Blood Tests for Tenofovir Users

HIV and Hepatitis B Testing

• HIV Testing: Before starting tenofovir as PrEP, an HIV test is necessary to confirm HIV-negative status. This test should be repeated at least every three months while on the medication, and immediately if another sexually transmitted infection is diagnosed or recent exposure to HIV is suspected.
• Hepatitis B Testing: Everyone should be tested for hepatitis B before or at the start of tenofovir treatment, regardless of whether they are using it for PrEP or hepatitis B treatment.

Kidney Function Tests

• Serum Creatinine and Creatinine Clearance: These tests assess kidney function. For PrEP users, tenofovir is not recommended if creatinine clearance is below 60 mL/min. If kidney function decreases during treatment, the cause should be evaluated.
• Urine Glucose and Urine Protein: These tests help detect kidney damage, which can occur with tenofovir use.
• Serum Phosphorus: In patients with chronic kidney disease, monitoring serum phosphorus levels is important as tenofovir can cause renal tubular injury, leading to conditions like Fanconi syndrome.

Liver Function Tests

• For those using tenofovir for hepatitis B, liver function should be monitored closely both during treatment and for several months after discontinuation. This is due to the risk of severe acute exacerbations of hepatitis B when stopping the medication.

Frequently asked questions

What should I do if my kidney function tests show abnormalities? If your kidney function tests, such as creatinine clearance, show abnormalities, it's important to discuss this with your healthcare provider. They may reassess the benefits of continuing tenofovir and explore other potential causes of kidney impairment.

Why is regular HIV testing important for PrEP users? Regular HIV testing ensures that PrEP users remain HIV-negative, as tenofovir should not be used alone in those who are HIV-positive. This helps prevent the development of drug-resistant HIV strains.

How often should I have liver function tests while on tenofovir for hepatitis B? Liver function tests should be conducted regularly during treatment and for several months after stopping tenofovir to monitor for any exacerbations of hepatitis B.

When to see a doctor

Seek medical advice if you experience symptoms such as unusual fatigue, swelling in your legs or feet, or changes in urination patterns, as these can indicate kidney problems. Additionally, if you suspect recent exposure to HIV or if you experience symptoms of liver problems, such as jaundice (yellowing of the skin or eyes), consult your healthcare provider promptly.

Decisions about your health and treatment should always be made in consultation with your healthcare provider.