Since molette (aka sludge) took offense at my original post, here is a link to a scholarly paper discussing the underlying science related to this topic.
http://www.asiaandro.com/news/upload/20 ... 20099a.pdf
And another reference
http://isoforlab.com/phocadownload/csli/C28-A2.pdf
Comparing Lab Results from Different Labs
Comparing Lab Results from Different Labs
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Last edited by JDS74 on Tue Nov 19, 2013 8:48 am, edited 3 times in total.
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Re: Comparing Lab Results from Different Labs
You said...
"For example: my most recent ferritin test returned a value of 274 mcg/L ( micrograms per Liter ).
The reference range was from 30 mcg/L - 400 mcg/L.
This means the for the population of folks on which the test was calibrated ( they did not have any medical condition related to the test in question), the average value for the test was 215 mcg/L {(30+400)/2}.
In this case, my result was in the upper half of the range and was considered normal."
That's not what it means at all. All it means is that any person who has a (measured/tested) amount of ferritin within that range is considered to have a 'normal' amount of ferritin. It does NOT mean they have NO medical condition related to whatever amount of ferritin their results showed. You may have a normal amount of ferritin (or any other e.g. component of blood, or other related fluid or chemical, etc.) but if those other components are abnormal, having a 'normal' ferritin test may be misleading and together with the abnormal results of other components point to various conditions you don't want to have. In other words other a normal amount of ferritin could be seen as ABnormal if amounts of related fluids, are skewed in relation to the ferritin.
"For example: my most recent ferritin test returned a value of 274 mcg/L ( micrograms per Liter ).
The reference range was from 30 mcg/L - 400 mcg/L.
This means the for the population of folks on which the test was calibrated ( they did not have any medical condition related to the test in question), the average value for the test was 215 mcg/L {(30+400)/2}.
In this case, my result was in the upper half of the range and was considered normal."
That's not what it means at all. All it means is that any person who has a (measured/tested) amount of ferritin within that range is considered to have a 'normal' amount of ferritin. It does NOT mean they have NO medical condition related to whatever amount of ferritin their results showed. You may have a normal amount of ferritin (or any other e.g. component of blood, or other related fluid or chemical, etc.) but if those other components are abnormal, having a 'normal' ferritin test may be misleading and together with the abnormal results of other components point to various conditions you don't want to have. In other words other a normal amount of ferritin could be seen as ABnormal if amounts of related fluids, are skewed in relation to the ferritin.
Re: Comparing Lab Results from Different Labs
Deleted
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Last edited by JDS74 on Tue Nov 19, 2013 7:53 am, edited 2 times in total.
Re: Comparing Lab Results from Different Labs
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Last edited by JDS74 on Mon Nov 18, 2013 8:37 am, edited 1 time in total.
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Re: Comparing Lab Results from Different Labs
I am sure everything said in this thread is reasonably true, until politics and money become involved and maybe even integrative medicine.
Just look at the new normal recommendation for statin drugs. The new normal is everyone needs to buy and use statins.
Look at vitamin D. There is a range of 30-100 for normal. Generally accepted seems to be 31 you are good 29 you are deficient. Some practitioners recommend above 50 helps avoid some maladies others suggest above 75 adds to the list of maladies that can be avoided.
So normal avoids deficiency diseases, "optimal" may avoid seemingly unrelated diseases through regulation of numerous bodily functions.
Just look at the new normal recommendation for statin drugs. The new normal is everyone needs to buy and use statins.
Look at vitamin D. There is a range of 30-100 for normal. Generally accepted seems to be 31 you are good 29 you are deficient. Some practitioners recommend above 50 helps avoid some maladies others suggest above 75 adds to the list of maladies that can be avoided.
So normal avoids deficiency diseases, "optimal" may avoid seemingly unrelated diseases through regulation of numerous bodily functions.
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Re: Comparing Lab Results from Different Labs
Deleted - I'm not continuing the conversation
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Last edited by JDS74 on Mon Nov 18, 2013 8:38 am, edited 1 time in total.
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Re: Comparing Lab Results from Different Labs
I think the best thing to do then is have other testing (of other parameters) and come to consensus based on overall results. One test based on one (or two) scales may or may not tell you a lot in isolation. You could always talk to proponents of one of the scales and ask why and how they justify a different range of normal from the other scale, but in the end I think it's a bit like semantics - pointless to argue or worry about without more to go on, like how you feel, what other tests point to, etc. etc.
Re: Comparing Lab Results from Different Labs
The problem with public perceptions of medical testing is that a medical test is called a "test."
To the layman, that word suggests that it involves a black-and-white, either-or "answer" upon which there can be easy consensus--as there may have been with true-or-false TEST answers in grammar school.
A medical test is rarely like that. A medical test is generally an inexact tool that provides limited imperfect information that may, or may not, be of use to a clinician in the context of other often-more-useful data. The test may only be useful for providing one shadowy, fuzzy picture of a mostly random instant in time to be compared to other instances in time for that patient or in comparison to other patients. It may be used more to point to a treatment than to point to an exact diagnosis.
Good docs often understand this. Patients and bad docs sometimes do not.
Some docs now refrain from running a test that might be helpful; those docs are afraid the patient or other docs of the patient will misuse the inexact results of the test.
A test may indicate a likelihood but not be conclusive in and of itself. The reasons are myriad. Not just means or calibration or targeted populations.
It is a true that a test may not be comparable to other tests in other locations conducted by other people. But many tests are, in practice, also not comparable to the same test in the same location conducted by the same people.
That's what makes discussion of many tests so testy.
IMO. As nothing medical.
I enjoyed your posts, JDS74. So I'm sorry to see them deleted, although you are perfectly within your rights to do so, of course.
Good posts spark controversial responses. That's what forums are for. Keep at it. That's how we all learn. From others' viewpoints. Personally, I find I often learn the most from the posts with which I agree the least or the posts to which I react most emotionally. But hey, that's just me.
To the layman, that word suggests that it involves a black-and-white, either-or "answer" upon which there can be easy consensus--as there may have been with true-or-false TEST answers in grammar school.
A medical test is rarely like that. A medical test is generally an inexact tool that provides limited imperfect information that may, or may not, be of use to a clinician in the context of other often-more-useful data. The test may only be useful for providing one shadowy, fuzzy picture of a mostly random instant in time to be compared to other instances in time for that patient or in comparison to other patients. It may be used more to point to a treatment than to point to an exact diagnosis.
Good docs often understand this. Patients and bad docs sometimes do not.
Some docs now refrain from running a test that might be helpful; those docs are afraid the patient or other docs of the patient will misuse the inexact results of the test.
A test may indicate a likelihood but not be conclusive in and of itself. The reasons are myriad. Not just means or calibration or targeted populations.
It is a true that a test may not be comparable to other tests in other locations conducted by other people. But many tests are, in practice, also not comparable to the same test in the same location conducted by the same people.
That's what makes discussion of many tests so testy.
IMO. As nothing medical.
I enjoyed your posts, JDS74. So I'm sorry to see them deleted, although you are perfectly within your rights to do so, of course.
Good posts spark controversial responses. That's what forums are for. Keep at it. That's how we all learn. From others' viewpoints. Personally, I find I often learn the most from the posts with which I agree the least or the posts to which I react most emotionally. But hey, that's just me.
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Sludge
Re: Comparing Lab Results from Different Labs
Perhaps, but that's not why he pulled his post. He pulled it because after further research, he discovered that the explanation made absolutely no sense:jnk wrote:Good posts spark controversial responses.
JDS74 wrote:Sometimes we get lab results from different labs that are testing for the same thing. This happens when one doctor orders a test and sends you to his favorite lab while another doctor orders a test and off you go to a different lab.
In order to compare the results and see if they are the same, it is necessary to convert the results to what is called a Z-score.
Lab results are reported as some numeric value and a corresponding reference range. If the different labs use the same test protocol, the reference range will be the same.
For example: my most recent ferritin test returned a value of 274 mcg/L ( micrograms per Liter ).
The reference range was from 30 mcg/L - 400 mcg/L.
This means the for the population of folks on which the test was calibrated ( they did not have any medical condition related to the test in question), the average value for the test was 215 mcg/L {(30+400)/2}.
In this case, my result was in the upper half of the range and was considered normal.
To understand "how normal" we need to convert the 274 to a Z-score.
When tests are being calibrated, the normal reference range is calculated to be the mean (average) +- 2 standard deviations from the mean. So the reference range is 4 standard deviations long. In this case, (400-30)/4 or about 92.5 mcg/L.
To get the Z-score, we subtract the mean (215) from the test value reported (274) and divide the result by the standard deviation (92.5) and we get a value of +0.64 rounded off.
Now suppose another test was done and the value reported was the same, 274. Only this time, the reference range for this test was 200-600. We could think the test value was the same so the results are the same. That would be incorrect.
Converting to a Z-score we get:
Mean = (600+200)/2 = 400
Standard Deviation = (600-200)/4 = 100
Z-score = (274-400)/100 = -1.29
The second lab is reporting a dramatic drop from +0.64 to -1.29 so we should ask what is going on.
Both results are in the normal range (-2.0 < Z < +2.0) so looked at separately, they would appear to be normal results.
That's why your doctor is usually not too interested in lab results for labs he/she doesn't usually use. Without this calculation, they can't compare results from different labs.
Re: Comparing Lab Results from Different Labs
Sludge
You are dead wrong.
I pulled the posts because there is no use in arguing with some one who deliberately misstates the discussion in order to prove they are the smartest person in the room.
And then they compound the insult with a personal attack.
You are dead wrong.
I pulled the posts because there is no use in arguing with some one who deliberately misstates the discussion in order to prove they are the smartest person in the room.
And then they compound the insult with a personal attack.
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Sludge
Re: Comparing Lab Results from Different Labs
Not even!
You are making numerous incorrect assumptions. First, you are assuming that each lab has established their own reference ranges. They do not. In practice, they will take what the manufacturer tells them, and may alter them on the opinion of their medical director based on clinical research. Consequently, the actual lab results can (and should) be exactly the same. This would be verified by comparing PT.
Secondly, you're a big baby.
You are making numerous incorrect assumptions. First, you are assuming that each lab has established their own reference ranges. They do not. In practice, they will take what the manufacturer tells them, and may alter them on the opinion of their medical director based on clinical research. Consequently, the actual lab results can (and should) be exactly the same. This would be verified by comparing PT.
Secondly, you're a big baby.
Re: Comparing Lab Results from Different Labs
I assume that when someone posts a summary of a personal understanding of how medical processes work, someone is thinking out loud in order to find out how other people understand the process. Otherwise, the person would simply link to a scholarly discussion of the matter at an authoritative site and be done with it.
What I like about the original post is that it raises questions for discussion that are interesting, such as the following.
Why do docs so often seem to have favorite labs and so often seem to reject findings from other labs?
Why do some docs like sticking to one lab over time when attempting to trend a biological process that any number of labs could measure?
When a test result comes back within normal range, does that prove nothing is wrong? And if so, with what level of certainty?
A patient may expect all lab tests to be as interchangeable as measurements taken of body temperature, weight, or blood pressure in multiple doctors' offices. Is that a reasonable expectation for other medical tests that are done over time from multiple labs?
My question is, When did lab tests transform into tools used by insurance companies to qualify, or disqualify, patients for treatments? Didn't medical testing used to be about providing tools for clinicians to use in the art of diagnosis and treatment of individual patients?
Or was that only the case on the planet I used to live on years ago?
Try to be nice, Sludge. Argue ideas and facts in evidence. No need for attack. Humility and graciousness will not undermine your contributions one iota in the cpaptalk lab of public opinion, no matter who tests your words. Even seasoned pitchers from the big leagues pitch underhanded when playing in the public park.
What I like about the original post is that it raises questions for discussion that are interesting, such as the following.
Why do docs so often seem to have favorite labs and so often seem to reject findings from other labs?
Why do some docs like sticking to one lab over time when attempting to trend a biological process that any number of labs could measure?
When a test result comes back within normal range, does that prove nothing is wrong? And if so, with what level of certainty?
A patient may expect all lab tests to be as interchangeable as measurements taken of body temperature, weight, or blood pressure in multiple doctors' offices. Is that a reasonable expectation for other medical tests that are done over time from multiple labs?
My question is, When did lab tests transform into tools used by insurance companies to qualify, or disqualify, patients for treatments? Didn't medical testing used to be about providing tools for clinicians to use in the art of diagnosis and treatment of individual patients?
Or was that only the case on the planet I used to live on years ago?
Try to be nice, Sludge. Argue ideas and facts in evidence. No need for attack. Humility and graciousness will not undermine your contributions one iota in the cpaptalk lab of public opinion, no matter who tests your words. Even seasoned pitchers from the big leagues pitch underhanded when playing in the public park.
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Sludge
Re: Comparing Lab Results from Different Labs
Hey, I was and did there, Jeff. He's the guy trying to "look smart" and then run a cover-up.jnk wrote:Try to be nice, Sludge. Argue ideas and facts in evidence.
I can't help it if he made himself look...
Oh right.
Nice.
Re: Comparing Lab Results from Different Labs
Sludge wrote:Hey, I was and did there, Jeff. He's the guy trying to "look smart" and then run a cover-up.jnk wrote:Try to be nice, Sludge. Argue ideas and facts in evidence.
I can't help it if he made himself look...
Oh right.
Nice.
PUBLIC ANNOUNCEMENT: "Anyone wanting to look smart should not try to do so in a public forum, since smart people never post in public forums."
There. That should cover it.
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Cereal Killer
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- Joined: Tue Jan 31, 2012 1:49 pm
Re: Comparing Lab Results from Different Labs
PUBLIC ANNOUNCEMENT: "Anyone wanting to look smart should not try to do so in a public forum, since smart people never post in public forums."
There. That should cover it.
Except you have confused "smart" with "wise".
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