test accuracy

[Paniccity]

how often are EFGR tests inaccurate?

[S_dillow]

they react to things like dehydration,medicine,even if you eat before the lab.inaaacurate?changes with situation is more like it.my egfr bounces up and down like a ball but seems to stay in a certain range so i hope that helps a little.

[orangecity41 NKF Ambassador in reply to S_dillow]

Agree with you. I tend to take an average. Believe too that medicine changes might possibly effect the test results.

[HisLittleOne in reply to S_dillow]

The most accurate kidney function test is cystatin C — it does not fluctuate with your diet or fluid intake and it represents the true picture of your kidney function. You can ask your doctor for the test or purchase it yourself online.

[Marvin8 in reply to HisLittleOne]

I'm one of the biggest fans around of the cystatin-c test, but it is not the most accurate test. Just like creatinine, it's a surrogate test. If you want the best eGFR estimation, recent studies suggest that the COMBINED creatinine + cystatin-c formula is your best bet. Reason? There can be confounding variables in both creatinine and cystatin-c that throw off the results, but the two tests combined tend to cancel out those variables.

[BrookeGrove in reply to Marvin8]

You are correct Marvin. the combined test is most accurate. The cystatin test will inflate the score. Also, the creatinine blood test and albumin test play in to the diagnosis.

[S_dillow in reply to HisLittleOne]

thank you thats the one i was trying to remember

[TES72 in reply to HisLittleOne]

TY 😇 I went into septic shock, in 2017. My kidneys and liver had shut down before I arrived at the ER. Currently, CJD 3B. I have a million questions. However, I just found this site. The physicians in area I have been, hear post septic shock syndrome and go deaf. 😆 🤣

[renancarlos]

Do you mean how often the actual tests give inaccurate results? For example, when your real eGFR was 80 and the test gave you 60.

Or how often the exams give inaccurate representations of your eGFR? For example, when you are dehydrated your eGFR can drop 15 points from your actual baseline.

[TableTennisMama]

Here’s the experience I had that compares two of the same exact tests, from the same lab and the exact same vial of blood: I had two blood orders from two different doctors that I carried into Labcorp. I asked them specifically to NOT duplicate any test because my insurance would not pay for that. They assured me they would not. But of course, they did duplicate the EGFR test. I don’t remember the exact numbers but one result was in the high 30s, the other was in the low 30s. It was significant enough difference to really ruin my confidence in the individual number that you get each time your blood is tested. My nephrologist assured me that it was no big deal, and that is why you look at your results over a period of time.

[Darlenia in reply to TableTennisMama]

Totally agree! My husband's nephrologists constantly analyze and study creatinine, BUN, proteins, and more - all the very specific hard data - and no so much eGFR. eGFR is an estimate really - with variables thrown in such as age and sex. Until recently, they also included race - never mind that a tiny black person was considered to be a heftier black person based on some crazy profiling. It's truly an estimate of how long you can go without expecting too much trouble. But trouble can come anyway - very important to realize this. My husband was placed on emergency dialysis with doctors intently studying everything, but eGFR. And the same thing happened when he was given a transplant.

[CrazyFloridian in reply to TableTennisMama]

I have been a medical laboratory scientist for many, many years. The eGFR stands for ESTIMATED Glomerular Filtration Rate, using your serum creatinine level, it is not a measured analyte, it is a calculation done by the instrumentation. It can be affected by your muscle mass, hydration status, age, pregnancy, and even some medications. The creatinine is measured using an automated instrument. Measurements, for the most part, should not vary more than 10% of each other (depending on the test and the instrument), so I would be interested to know what your 2 actual creatinine (or eGFR) were to see the difference. The instruments themselves are run, maintained and kept within quality control standards by educated and certified (and in some states, licensed) medical laboratory scientists. One example of maintenance is precision. We have to determine if the instrument can reproduce results accurately. A 31 eGFR and a 38 eGFR (for example) would not be within 10% of each other, but the creatinine level used to calculate it may have been. Without seeing the actual results that you received, it is hard to say.

Mistakes do happen, as humans are humans. There are pre-analytical, analytical and post-analytical processes that are constantly monitored to ensure that the laboratory results that we produce are accurate, but sometimes things happen.

And for renancarlos above, your eGFR changing due to your hydration status does not reflect poorly on the laboratory, that is a variable for which we have no control!

[Paniccity in reply to CrazyFloridian]

I had two blood tests one month apart. The first one was 47 and the second one was 78. It was at two different labs. The only other variable I can think of was that I was taking creatinine supplement a month before the first blood test. Would that have been reflected in low efgr result?

I stopped taking the supplement immediately after first blood test. I have no idea if that’s why the second blood test came out normal.