Re: Protein in urine

On May 1, 8:15 pm, Hogw...@xxxxxxxxxxxxx wrote:
I notice a test for protein in the standard blood/urine annual
check-up tests.

Two different interpretations as it is normal to have protein in blood
but abnormal to have protein in urine.


1) The body produces tens of thousands of different proteins. Which
protein are we talking about?

The blood test is a nonspecific biochemical test for all proteins. The
urine test for protien is more sensitive to albumin compared to other
proteins. It does detect all proteins.


2) Depending on the answer to (1), do we know which protein is
produced by which cell and which organ?

It is not really important which cell or organ. There are specific
protein assays that can be used in evaluating diseases that may
produce an increase in a specific protein. One initially does a screen
for all proteins and subsequent testing can divide or test for
specific proteins. Apart from the total protein test, the albumin test
is one of those specific proteins. It is common to have a total
protein and albumin performed.


3) What's the resolving power of the urine tests? The lab website and
of course the lab report don't say. Since we seem to be able to detect
parts per billion of things like lead can we do the same here (e.g. 1
molecule of x protein in 50 ml urine sample).

Good question. The resolving power in technical terms refers to the
sensitivity of the test. The usual screen for protein in urine has a
lower sensitivity of 30 mg/dl. levels lower than this will give a
negative protein screen as performed by a urinalysis dipstick test.
Microalbumin refers to a specific test designed to detect occult
albumin low levels and thus the term micro-albumin. In reality it is
simply a more sensitive test methodology used in detecting albumin
levels in urine not normally detected by urinalysis screening.

You can see below the sensitivities involved in lower limit
detections. The test used is dependent on the purpose of the test.
There are clinical indications which determine which is the better
test along with proper interpretation of such test. The ultimate goal
in any test is it's clinical utility. Having a test being able to
detect one-in-a-trillion parts is not really important if it has no
clinical utility. The clinical utility is how well a test separates a
normal person from a disease condition. If there is too much overlap
between false negatives and false positives then it is not a really
good test.


http://www.idexx.com/animalhealth/laboratory/diagnosticupdates/diagnosticupdate1.jsp


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Relevant Pages

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