[Note: This entry was actually written in Sep 2009. I changed the posting date to keep my blog entries in chronological order.]
by George Taniwaki
Today, I am getting a physical exam and having blood samples drawn to conduct some tests (complete blood count, serum creatinine, and hepatitis panel). I’m doing this in order to complete a medical certificate required by National Kidney Registry.
I haven’t been to a doctor in several years, and I don’t currently have a primary care physician. So I just picked one out of my medical insurance plan’s website. I guess I should have a physician and a baseline physical exam. Thus, I justify this as a legitimate medical expense and will charge it to my insurance company rather than pay for it out-of-pocket.
The physical exam includes a creatinine clearance rate test to determine if my kidneys are functioning normally. The test requires knowing (1) the concentration of creatinine in my blood plasma, which is measured by the blood test mentioned above and (2) the rate my kidneys extract creatinine (in mg/minute) from my blood. This latter value is calculated by using a full-day sample of my urine.
|What is it?||Creatinine clearance rate test|
|Why is it needed?||Ensures your kidney function is normal|
|How is it done?||A 24-hour urine samples is taken along with a blood sample. The amount of creatinine (a normal waste product produced by your muscles) in your urine and blood is measured and the rate it is being removed by your kidneys is calculated|
|Preparation||Reserve a spot in your refrigerator for the sample bottle. Review the instructions before starting|
|Test time||A few minutes to take blood sample. One day to collect the urine sample plus the time to deliver the urine sample to the lab. A few hours to run the test itself (you do not have to wait for the results)|
|Discomfort||A needle prick in the forearm, there may be a slight bruise. You have to urinate into the sample bottle for a day|
The doctor sends me home with a special orange one-gallon (3.5-liter) jug and tells me to collect all of my urine starting tomorrow morning and ending the next morning. The exact instructions are as follows:
- Temporarily stop taking any medications that can interfere with the test results. In my case, there are none
- First thing in the morning on day 1, urinate into the toilet (not the specimen bottle). Write the exact date and time (to the minute) on the bottle
- Try to drink extra fluids during the test period. This makes measuring the volume easier and more accurate
- For rest of the day and overnight, collect all urine in the specimen bottle. Keep the bottle capped and refrigerated (or in a cool, dry, dark place)
- On the morning on day 2, about the same time as previous day, collect urine in the specimen bottle. Write the exact date and time (to the minute) on the bottle
- Label the bottle with your name. Drop off the specimen at the lab (not the doctor’s office) within 4 hours
- If you miss collecting any urine, stop immediately, dump the urine into the toilet and repeat the test starting the next morning. However, because of the delay, if this happens, request that a new blood sample be taken
Note that even if you drink a lot of fluids you will not come anywhere near filling the jug.
Using this sample, the lab can calculate my creatinine clearance rate. They will know how much urine I produced (in ml) during a known amount of time (in min). By dividing the volume by the time, they can calculate my average urine production rate (in ml/min). The lab will take a small sample of urine from the bottle and measure the concentration of creatinine in my urine (in mg/ml). Multiplying this result by my urine production rate and dividing by the concentration of creatinine in by blood (in mg/ml) gives the creatinine clearance rate (in ml/min).
Note to self: remember not to confuse this jug with the OJ in the morning.
One-gallon (3.5-liter) specimen jug. Photo from General Plastic
For more information on becoming a kidney donor, see my Kidney donor guide.
[Update1: I repeat the 24-hour urine test twice more in Sep 2009.]
[Update2: I clarified the instructions above so other patients will know how to do the test correctly.]
[Update3: Added a summary table.]