LabCorp Vs Quest free testosterone lab ranges: Why are they different?

[GeorgieBoy]

Quest Diagnositcs' range is 35-155 pg/mL for Free Testosterone. That's 3.5-15.5 ng/dL.

Labcorp's range is 9-25 ng/dL.

That's a big difference. 3.5-15.5 and 9-25.

My question is: If you tested at 25 ng/dL on a Labcorp test, does that mean you would've tested at 15.5 ng/dL on the Quest Diagnostics test? Or would you have also tested at 25 ng/dL on the QD test?

LabCorp and Quest Laboratories have different reference ranges for serum testosterone assays and free testosterone lab ranges. Here are the details:

- According to the Quest website, the normal testosterone reference range for men is 250-1110 ng/dL[1].
- LabCorp's range for free testosterone is 9-25 ng/dL[2].
- Quest Diagnostics' range for free testosterone is 35-155 pg/mL, which is equivalent to 3.5-15.5 ng/dL[2].
- The concentration of free testosterone is typically <2% of the total testosterone concentration, and most of the total circulating testosterone is bound to sex hormone-binding globulin (SHBG) and albumin[3].
- Routinely available assay methods used to measure total testosterone are not sensitive enough to accurately quantitate the free testosterone fraction directly. Free testosterone is estimated in some tests by a direct, analogue enzyme immunoassay (EIA) [3].
- The difference in reference ranges between LabCorp and Quest may be due to different test methods used[4].
- Testosterone, Free, Bioavailable and Total, MS is a test offered by Quest Diagnostics that is helpful in assessing testicular function in males and managing hirsutism and virilization in females[5].
- Some users on forums have reported discrepancies between LabCorp and Quest's free testosterone ranges, with Quest's range being significantly higher than LabCorp's[4][6].

Citations:
[1] LabCorp VS Quest Laboratories Serum Testosterone Assays & Reference Ranges
[2] LabCorp Vs Quest free testosterone lab ranges: Why are they different?
[3] 144980: Testosterone, Free, Direct | Labcorp
[4]

https://www.reddit.com/r/Testosterone/comments/c68v2v

[5] Quest Diagnostics: Test Directory
[6] Beware of Which Testosterone Test from Quest Labs

 

[DorianGray]

I was wondering the same thing from my lab tests. Apparently so. You can compare results here:

Help With Lab Results and TRT

Started TRT and HCG 5/16/20. Now, symptoms of fatigue, periodic, mild anxiousness (almost shaky), mild brain fog. Here is Lab before starting TRT/HCG:

www.excelmale.com

@GeorgieBoy did you have the tests done? What were your values?

 

[madman]

Quest Diagnositcs' range is 35-155 pg/mL for Free Testosterone. That's 3.5-15.5 ng/dL.

Labcorp's range is 9-25 ng/dL.

That's a big difference. 3.5-15.5 and 9-25.

My question is: If you tested at 25 ng/dL on a Labcorp test, does that mean you would've tested at 15.5 ng/dL on the Quest Diagnostics test? Or would you have also tested at 25 ng/dL on the QD test?

Never compare different assays let alone reference ranges from different labs.

When getting blood work stick to using the same lab/assays (most accurate).

Regarding free testosterone, the most accurate assay is the gold Standard Equilibrium Dialysis or Ultrafiltration (next best).

Forget relying on the direct immunoassay or linear law-of-mass action Vermeulen calculated method.




LABCORP:

EQUILIBRIUM DIALYSIS

500726: Testosterone, Free, Mass Spectrometry/Equilibrium Dialysis (Endocrine Sciences) | Labcorp

Labcorp test details for Testosterone, Free, Mass Spectrometry/Equilibrium Dialysis (Endocrine Sciences)

www.labcorp.com

EQUILIBRIUM ULTRAFILTRATION

081786: Testosterone, Free, Equilibrium Ultrafiltration With Total Testosterone | Labcorp

Labcorp test details for Testosterone, Free, Equilibrium Ultrafiltration With Total Testosterone

www.labcorp.com

NELSONS DiscountedLabs

Testosterone, Free (Equilibrium Dialysis) and Total, MS - Most Affordable and Accurate Test

Get an affordable and accurate testosterone test results with our Total Testosterone, M and Free (Equilibrium Dialysis) test. Visit DiscountedLabs.com for more information.

www.discountedlabs.com

Look over post #13

Complete apathy/depression from too high E2?

I started TRT 5 weeks ago on 24mg/day subcutaneous injections of Test C (168mg/week). My doc put me on a relatively high dose because my SHBG is very high (maybe 2-3 standard deviations out of range), so much so that despite having naturally high TT levels, my FT was in the dumpster all the way...

www.excelmale.com

 

[madman]

Unfortunately, when it comes to the reference ranges for measured or calculated FT they vary between different labs, and as of now, there is no standardization let alone a harmonized reference range.

Efforts are underway to standardize the procedures for FT and to generate harmonized reference ranges.

The best bet is to use the most accurate testing methods such as the gold standard Equilibrium Dialysis or Ultrafiltration (next best) if you truly want to know where your FT level sits.

Regarding calculated, there are flaws in the old linear law-of-mass action models such as the most commonly used Vermuelen.

 

[madman]

Quest Diagnositcs' range is 35-155 pg/mL for Free Testosterone. That's 3.5-15.5 ng/dL.

Labcorp's range is 9-25 ng/dL.

That's a big difference. 3.5-15.5 and 9-25.

My question is: If you tested at 25 ng/dL on a Labcorp test, does that mean you would've tested at 15.5 ng/dL on the Quest Diagnostics test? Or would you have also tested at 25 ng/dL on the QD test?

Two completely different assays.

Quest is Equilibrium Dialysis and Labcorp is the Direct analog enzyme immunoassay (EIA).

Your FT from Quest ED 35-155 pg/mL is the most accurate and the one that truly matters.

 

[DorianGray]

The choice of labs, then would seem critical, no? That is, if a doctor relies on a Lab Corp and finds 927 acceptable, yet the Quest Lab shows 1615, he would question his TRT dosing wouldn't he? Such was the case with my labs. (the latter used dialysis).

 

[GeorgieBoy]

I was wondering the same thing from my lab tests. Apparently so. You can compare results here:

Help With Lab Results and TRT

Started TRT and HCG 5/16/20. Now, symptoms of fatigue, periodic, mild anxiousness (almost shaky), mild brain fog. Here is Lab before starting TRT/HCG:

www.excelmale.com

@GeorgieBoy did you have the tests done? What were your values?

Before I forget, your DHT is at 500 out of a range of 30-85. That seems like it can't be a good thing. Are you on the cream?

The labs aren't even close, it's very interesting. On Labcorp your TT is top of the range, but on Quest your TT is 1.5x the top of the range. Labcorp FT is 30% above the top of the range, but Quest FT is almost 200% above the top of the range.

Also, your Labcorp FT range is 6.6-18, my Labcorp range is 9-25. I've always wondered whether they adjust by age. Are you older than 40 by any chance?

 

[GeorgieBoy]

Two completely different assays.

Quest is Equilibrium Dialysis and Labcorp is the Direct analog enzyme immunoassay (EIA).

Your FT from Quest ED 35-155 pg/mL is the most accurate and the one that truly matters.

Thanks for all the information, this is really helpful. I had no idea Labcorp only had the Direct method for Free T. I'm doing my labs through discountedlabs and I think they only use Quest Diagnostics, so that's good.

 

[madman]

Thanks for all the information, this is really helpful. I had no idea Labcorp only had the Direct method for Free T. I'm doing my labs through discountedlabs and I think they only use Quest Diagnostics, so that's good.

They also have Equilibrium Dialysis and Ultrafiltration (post #3 above) but you chose to get the direct immunoassay.

 

[madman]

The choice of labs, then would seem critical, no? That is, if a doctor relies on a Lab Corp and finds 927 acceptable, yet the Quest Lab shows 1615, he would question his TRT dosing wouldn't he? Such was the case with my labs. (the latter used dialysis).

Just replied to your previous thread.

 

[DorianGray]

Before I forget, your DHT is at 500 out of a range of 30-85. That seems like it can't be a good thing. Are you on the cream?

The labs aren't even close, it's very interesting. On Labcorp your TT is top of the range, but on Quest your TT is 1.5x the top of the range. Labcorp FT is 30% above the top of the range, but Quest FT is almost 200% above the top of the range.

Also, your Labcorp FT range is 6.6-18, my Labcorp range is 9-25. I've always wondered whether they adjust by age. Are you older than 40 by any chance?

You make all the points that puzzle me also. Yes, I use the cream-3 pumps. 1 scrotal, 2 shoulder. I've used Test Cypionate injection before and felt better. Things were not quite out of whack. I'm age 69.

 

[GeorgieBoy]

You make all the points that puzzle me also. Yes, I use the cream-3 pumps. 1 scrotal, 2 shoulder. I've used Test Cypionate injection before and felt better. Things were not quite out of whack. I'm age 69.

Any reason you're sticking with the cream if you felt better with injections? Have you tried something like every day intramuscular of SubQ injections to see if you can reach stable levels you feel good at?

I'm not anything close to a doctor but I can't imagine that having DHT at 600% the top of the normal range is good long term.

 

[DorianGray]

I only went with the cream because it was the doctor’s recommendation. Especially since my chief complaint was low libido so the testicular application was to increase dht and hence libido. Worked early on and then didn’t. From my experience so far I’m learning my body reacts wildly to hormone adjustment. Even one doc thought my thyroid was in the low range so he put me on an OTC thyroid supplement and it shot up to hyperthyroid range in a matter of weeks.

 

[JimGainz]

Quest does this lame thing where they pick the midpoint of FT as the top end for men who’s blood work script shows Hypogonadism.

It causes a lot of confusion and was one of the reasons why it took me years to get help for low T. My Free T was 6.5 and my Endo kept telling me I was fine b/c I was mid range. Actually, I was the bottom 25% of the normal range.

Beware of this and make sure you inform your doctor. It can cause a misdiagnosis.

This is documented on one of the the Testosterone Nation TRT sticky’s which was how I found out about it a few years ago.

 

[madman]

Quest does this lame thing where they pick the midpoint of FT as the top end for men who’s blood work script shows Hypogonadism.

It causes a lot of confusion and was one of the reasons why it took me years to get help for low T. My Free T was 6.5 and my Endo kept telling me I was fine b/c I was mid range. Actually, I was the bottom 25% of the normal range.

Beware of this and make sure you inform your doctor. It can cause a misdiagnosis.

This is documented on one of the the Testosterone Nation TRT sticky’s which was how I found out about it a few years ago.

As long as people understand that most men do well with FT in the 20-30 ng/dL range and many would aim for the higher end it should make no difference.

If you want to get nit-picky than I would use Labcorp FT ED assay.

500726: Testosterone, Free, Mass Spectrometry/Equilibrium Dialysis (Endocrine Sciences) | Labcorp

Labcorp test details for Testosterone, Free, Mass Spectrometry/Equilibrium Dialysis (Endocrine Sciences)

www.labcorp.com

 

[JimGainz]

As long as they are measured in the same unit (eg NG/DL) then yes. An 800 total test level at Labcorp can be considered the equivalent at Quest. (Although different labs/processes would yield slightly different results, it should not be material)

 

[JimGainz]

Another thing - There are online calculators that can determine ones calculated Free Test based on Total T, Albumin and SHBG. It always comes up higher than the lab values. I don’t know which one is the true value.

 

[sammmy]

Quest does this lame thing where they pick the midpoint of FT as the top end for men who’s blood work script shows Hypogonadism.

It causes a lot of confusion and was one of the reasons why it took me years to get help for low T. My Free T was 6.5 and my Endo kept telling me I was fine b/c I was mid range. Actually, I was the bottom 25% of the normal range.

Beware of this and make sure you inform your doctor. It can cause a misdiagnosis.

This is documented on one of the the Testosterone Nation TRT sticky’s which was how I found out about it a few years ago.

Highly doubtful statement that Quest will deliberately pick the middle of the normal curve as the top normal value. Any lab test will measure a parameter related to the free testosterone, not the absolute amount of free testosterone. That is why the range of values for free T that the test gets different and tests are not comparable between each other even in the same units, nor are comparable to online calculators.

To determine normal range of their test, what they do probably is get a random sample of men, obtain the values their test give for that sample and plot a histogram. Ideally it should be a normal distribution and then ''normal range'' could be defined as values within two standard deviations from the mean. If the sample was really normal and quite large, it is highly unlikely that it will get the upper normal value in the middle of the actual population curve.

 

[sammmy]

Another thing - There are online calculators that can determine ones calculated Free Test based on Total T, Albumin and SHBG. It always comes up higher than the lab values. I don’t know which one is the true value.

Online calculators have their different ranges and cannot be compared to lab tests with their ranges. On top of that, online calculators calculate some averaged out curve for many people. If you are an outlier, they will give incorrect values for you.

Simply select one of the good lab tests for free T that Madman listed and stick to it.

There is no such issues with the Total T tests - they usually get similar values and have similar ranges.

 

[JimGainz]

Highly doubtful statement that Quest will deliberately pick the middle of the normal curve as the top normal value. Any lab test will measure a parameter related to the free testosterone, not the absolute amount of free testosterone. That is why the range of values for free T that the test gets different and tests are not comparable between each other even in the same units, nor are comparable to online calculators.

To determine normal range of their test, what they do probably is get a random sample of men, obtain the values their test give for that sample and plot a histogram. Ideally it should be a normal distribution and then ''normal range'' could be defined as values within two standard deviations from the mean. If the sample was really normal and quite large, it is highly unlikely that it will get the upper normal value in the middle of the actual population curve.

Believe it or not, this is exactly what Quest does. I have had tests from both labcorp and quest for over 4 years and the top end of Quest (using the same units of measurement) was 150 Ng/dL for Free T where as quest was 280. This has been well documented on other forums. If you don’t believe me, get your next labs drawn and quest and then the next one at Labcorp. As long as the diagnosis was hypogonadism Quests top end of free T will actually be the midpoint on Labcorp.