Track your cystine levels

Blood tests measure the amount of cystine in white blood cells

The secret to tracking how well your cystine-depleting therapy (CDT) is working is regular cystine level testing.

What is a cystine level test?

Cystine level testing measures the amount of cystine in your white blood cells (WBCs). Along with carefully following your treatment plan, routine testing is key. Testing is the only way to know your cystine level.

Why cystine level testing is important

Tracking cystine levels over time helps you and your doctor know how well your CDT is working. Knowing your cystine level will help your doctor decide if your dose needs to be adjusted. Having the correct dose is the only way to help delay or limit damage to your body.

Children should be tested 4 times a year, and adults should be tested 1 to 2 times a year. Talk to your doctor about making a testing plan to track results regularly.

Two cystine tests. Two target levels.

There are two types of cystine level tests. They measure your cystine levels differently.

Type of WBC cystine level tests Mixed leukocytes test Granulocytes test
Target cystine level range Below 1.0 nmol ½ cystine/mg protein Below 1.9 nmol ½ cystine/mg protein
Testing institution Baylor University University of California San Diego (UCSD)
When to get the test Your doctor will order WBC cystine level testing at the same point in your CDT dosing schedule.

It's important to work with your doctor to decide which cystine level test is right for you. You should always know which test you're taking because the results mean different things. Taking the same test each time may help you compare your test results over time.

Timing is everything

In people with cystinosis, cystine levels usually change based on the time of the last dose of cystine-depleting therapy (CDT). It's important to have your cystine levels tested at the right time in order to get useful test results. Ask your doctor what time of day you should be getting your cystine levels tested.

To get the most out of treatment, people living with cystinosis need to take their CDT regularly. It's very important to take your medicine at the same time every day and every night. Even the slightest delay can cause cystine levels to rise.

Tips for staying on track with testing

  • There are 2 types of cystine level tests, and it's important to know which test you're taking
  • Children should be tested 4 times a year and adults 1 to 2 times a year
  • Work with your doctor to make sure your cystine level test is given at the right time of day