The Constant Student

Last week, I was excited about a new word and, boy oh boy, did I learn even more about gastroparesis after my blog was posted on Facebook Kidney Disease Support Pages. This week, it’s a new test that a reader asked me about: the Iothalamate clearance test.

This is what the University of Washington at http://www.uwmedicine.org/health-library/Pages/iothalamate-scan.aspx had to say about the test:

“An Iothalamate study is a diagnostic nuclear medicine procedure used to find out your glomerular filtration rate (GFR) for each kidney….

How Does It Work?

A small amount of a radioactive material, called radiotracer, is injected into the muscle of your upper arm. This material is excreted out of your blood, into your urine, by glomerular filtration. By taking samples of your blood and urine over time, we are able to calculate what your GFR is. This gives your doctor information about the health of your kidneys.

How Do I Prepare?

  • Drink 20 ml of water per kilogram of body weight in the 90 minutes before arriving in the department. For most people, this is about 1 to 2 1-liter bottles of water.
  • Drink lots of fluids throughout the 4-hour study. The study may be continued for more time if more urine is needed.
  • You need to be able to empty your bladder completely.
  • Most patients are required to withhold diuretics the day of the test. Check with your doctor if you take diuretics.
  • Do not consume any caffeine the morning of the study.

How is the study performed?

  1. When you arrive at the lab, the technologist will check your blood pressure. You will need to completely empty your bladder into a container. The technologist will also place an IV into one of your veins and take a sample of your blood.
  2. The radioactive tracer will be injected into your upper arm muscle. The technologist will take another blood pressure reading about 10 minutes later.
  3. You will return every hour, for 4 hours. Each hour, the technologist will take a blood sample and ask you to completely empty your bladder into a container. It is very important that you do not go to the bathroom outside of the department.
  4. Throughout the study, you will be required to drink plenty of fluids, and avoid caffeine. You will be allowed to eat.
  5. After 5 urine and blood samples are collected, the IV will be removed and you are free to leave. This urine will be analyzed and measured.

What will I feel during the study?

Most people feel no different than normal during this study. Some people may feel a little shaky after the injection of the radiotracer. This is because a small amount of epinephrine is added to the radiotracer to improve its absorption. You may also have minor discomfort from holding your bladder….

Whoa, baby! Nuclear medicine? Radioactive material? Epinephrine? I understood why no diuretics, but why no caffeine? Any why was there an IV?

I know, I know. Start slowly. According to RadiologyInfo at https://www.radiologyinfo.org/en/info.cfm?pg=gennuclear,

“​Nuclear medicine is a branch of medical imaging that uses small amounts of radioactive material to diagnose and determine the severity of or treat a variety of diseases, including many types of cancers, heart disease, gastrointestinal, endocrine, neurological disorders and other abnormalities within the body. Because nuclear medicine procedures are able to pinpoint molecular activity within the body, they offer the potential to identify disease in its earliest stages as well as a patient’s immediate response to therapeutic interventions.”

Okay, got it. And radioactive?  MedicineNet at https://www.medicinenet.com/script/main/art.asp?articlekey=11952 defines the word this way:

“Radioactive: Emitting energy waves due to decaying atomic nuclei. Radioactive substances are used in medicine as tracers for diagnosis and in treatment to kill cancerous cells.”

As a side note, as far as I could tell this test is not used on pregnant women or those who are breastfeeding since a radioactive substance is involved.

I couldn’t decide if I was feeling better or worse about nuclear medicine to diagnose Chronic Kidney Disease. So I looked… and looked…and looked again before I realized it’s contrast dye that may cause injury in those with CKD, not radioactive material. No wonder some nephrologists have no compunction about ordering this test. By the way, radioactive exposure in this test is less than that in a CT scan.

Hmmm, epinephrine sounds familiar. Of course! My buddy back East carries an epi pen just in case she’s stung by a bee. Epinephrine is also known as adrenaline. Ah, so adrenaline “is added to the radiotracer to improve its absorption.” Makes sense.

Now that we know that epinephrine is adrenaline, we can easily understand why no caffeine. Remember that song, “Fly Me to the Moon”? Between the adrenaline and the caffeine, you’d be flying yourself to the moon.

What also makes sense is no diuretics. You wouldn’t want to be urinating more than necessary if your urine is being evaluated. That might dilute the very small amount of radioactive material that was injected into the muscle of your arm.

So, what’s the IV for you ask.  That’s how the radiotracer is injected and/or how the blood samples are obtained. I know I’d rather have one IV instead of four or five needle sticks for individual blood draws. Apparently, there are variations in how the test is administered.

 

Now the biggie: Why use this test at all? This is from the glossary in What Is It and How Did I Get It? Early Stage Chronic Kidney Disease:

“GFR: Glomerular filtration rate [if there is a lower case “e” before the term, it means estimated glomerular filtration rate] which determines both the stage of kidney disease and how well the kidneys are functioning.”

The Iothalamate clearance test is a measured GRF test. It doesn’t estimate, but actually measures your GFR, sort of like real time videos are not replays but live. Your doctor may doubt the results of your eGFR, the routine test, due to your serum creatinine output or some other variable. Age, race, gender, and muscle mass all affect the eGFR. The Iothalamate clearance test will give him an accurate measurement of your GFR so he will know not only what stage of CKD you are in, but how to treat it.

I hope this is helpful to the reader who asked.

Until next week,

Keep living your life!