You are focusing too much on the container itself.

Blood tubes have different anticoagulants in them. Some have none. These are
color coded for the convenience of everyone. For example, everyone knows
instinctively that blue top tubes are for coagulation testing. Purple tops
are mostly used for CBC's and are used as a whole blood specimen, i.e. not
centrifuged first. Once you get to know what types of specimens need to be
drawn for what tests, then it makes more sense. Many tests can be performed
off one tube, assuming that

a) there's enough blood in the tube to yield enough serum or plasma for the
test (most tubes are spun down in high speed centrifuges and the resulting
liquid is used for testing. The red cells are spun out. Serum results when
blood is allowed to clot in a tube without anticoagulant and then spun down.
Plasma results when you spin down a tube that has anticoagulant in it. EDTA
plasma comes from a purple top tube; citrated plasma comes from a blue top
tube, etc.)
b) tube is labelled correctly [but that's another show]
c) specimen is not "hemolyzed" (red cells burst causing the serum or plasma
to turn red - many tests cannot be run on hemolyzed specimens)

One tube can be aliquotted to different departments or different tubes for
different analyzers. Most analyzers use a specimen cup of some type,
although many use the blood tube itself - depends on the machine. Analyzers
have multiple channels that can use the same aliquot for many different
tests e.g. your electrolyte order you cited in your message.

Aliquotting specimens gets tricky when the patient is hard to stick and you
can't get a lot of blood from them. There are microtainers that you can use
to get away with short draws in some instances. It really depends on the
test ordered and the specimen required for that test. Some tests end up
getting cancelled because there's simply not enough specimen.

New LIS (laboratory infomation systems) software programs handle all this
aliquotting, specimen labelling, etc. quite well. It is much more
complicated than the olden days when I first trained as a medical
technologist. Back then you needed LOTS of blood. Analyzers used sometimes 1
ml per test. Nowadays 0.5 ml of serum can produce many test results because
the analyzers just don't need as much specimen as they used to need.  In the
olden days we would line up our tubes in the racks and hand label the
aliquot tubes. When the tubes clotted enough to spin, we put them in the
centrifuge. We poured or pipetted off the serum/plasma. We then spun them
again to be sure there were no red cells. This was in the days before the
SST gel tubes that provide a barrier between serum and cells. There are
still certain tests that must be drawn in tubes without anything in them,
however. It used to include some drug levels, as the SST gel could absorb
some of these drugs from the blood. I don't know about nowadays. Many things
have changed and I haven't worked in chemistry for nearly 20 years.

Hope this helps. Labs are complicated places. There are many steps involved
from patient to result reporting, and many possible places for pitfalls.
Correct specimen labelling is THE MOST IMPORTANT ISSUE in the whole string
of events. Without the proper specimen, all is for naught. If names on tubes
don't match names on requisitions, there are even bigger problems. There are
lots of checks and balances in the system to prevent this, but it still
happens. In microbiology we do not accept anything that doesn't match. If
it's a difficult specimen to recollect, i.e. cerebrospinal fluid (CSF) we
have to have someone come to the lab and sign for the specimen. An incident
report is written up. If it's just a urine or swab, it must be recollected.
To work in a lab you must be somewhat anal retentive about details. This is
a GOOD thing in a laboratory.

Judy Dilworth, M.T. (ASCP)
Microbiology

What you are asking neesd an answer which would be an essay thousands of
words long. Hospital labs are a LOT more complicated than you seem to
realise.
Your best move would be to visit one and see for yourself what is involved.

the person who sets up lab "dictionaries" in the LIS system; we use
Meditech, its pretty popular. So when a nurse goes to order "lytes"
the host generates a specimen label with a bar code which is affixed
at the time of collection; when the sample has been recieved and gone
through all the required pre-analytical steps, the  instrument  reads
the barcode,quieries the host computer and says "OK I've got to run Na
K, Cl and CO2 on this".

Again it's up to the lab to define how the labels are mapped to the
containers.
I think we have it set so each (typical low sample volume) test takes
0.01 of a test
tube for example, so up to 100 tests can be ordered on the same
specimen/tube.
You can also define it so a CBC for example takes 1 tube and an esr
takes another
or any fractional amount in between, you can also specify different
tubes with the same specimen number for different tests, for example
routine chemistry is done on a green top plasma tube, but tsh needs a
gold top serum tube, a label prints out for John Doe
specimen 2002 B1 barcode sticky label for a green top , 1 for gold
top., you can also print aliquot labels for when you have to split up
a specimen to farm it out to different testing benches or sites.

There is a lot that goes into the pre-analytical process. NCCLS
publishes quality standards for medical labs, its really too big an
area for me to go into right now.
There are also local state/ provincial regulations and standards to
comply with.

Thank you for generating more legit traffic than this site has seen in
a while!