Before you start PrEP and while you are on PrEP, your healthcare provider will monitor your kidney function by monitoring a value called "creatinine clearance."

What are creatinine and creatinine clearance?

“Creatinine” is a muscle waste byproduct that is eliminated through your kidneys. Your creatinine level is one way of measuring kidney health. Higher creatinine levels can indicate that your kidneys are slowing down. However, higher levels often result from normal things like diet, exercise, dehydration, or minor illness. It’s possible to have an elevated creatinine level even though your kidneys are perfectly fine.

“Creatinine clearance” is a number that is calculated based on your creatinine level but that also takes into account your age, sex, and weight. Most kidney specialists think that creatinine clearance gives a better picture of kidney health than creatinine level alone because creatinine clearance takes these other factors into account.

CDC guidance related to PrEP is based on creatinine clearance.

What factors can affect your test results?

Many factors can affect your creatinine level and creatinine clearance, including:

• Dietary supplements
• Drinking alcohol
• Not drinking enough water
• Getting too much sun

As one research report explained:

An increase in serum creatinine can result from increased ingestion of cooked meat (which contains creatinine converted from creatine by the heat from cooking) or increased intake of protein and creatine supplements, in excess of the recommended dosage. Creatine is present in the organs, muscles, and body fluids of animals. Creatine supplements promote protein synthesis and are a quickly available source of energy for muscle contraction, hence they are used to enhance athletic performance. Furthermore, intense exercise can increase creatinine by increasing muscle breakdown

What if your test results are abnormal?

If you get an abnormal test result, you may be concerned. However, CDC does not recommend that you stop PrEP based on a single test result. If you get a lab test that shows abnormal creatinine clearance, your doctor will order a second test to see if the results are the same. Before your second test, make sure you are well hydrated (drink plenty of water), and avoid creatine supplements, intense exercise, alcohol and excessive exposure to the sun.

When to consider stopping PrEP

It depends what medication you are taking.

• Truvada: If you are taking Truvada for PrEP (or a generic equivalent) and you have two consecutive test results that show your creatinine clearance is below 60, your healthcare provider may recommend you consider stopping PrEP, at least temporarily.
• Descovy: If you are taking Descovy for PrEP (or a generic equivalent) and you have two consecutive test results that show your creatinine clearance is below 30, your healthcare provider may recommend you consider stopping PrEP, at least temporarily.