Guys wrote in message ...

1.  The first assays were based on radioactive antibodies.

   Grab the insulin with a  radioactive antibody.
   Assay the radioactivity

Worth a Nobel Prize at the time.

Now there are several assays.    One type:

   coat a glass plate with a monoclonal antibody for insulin
   contact the glass plate with the sample,  the antibody grabs the insulin
   contact the antibody-insulin combo with another antibody linked to
biotin
   assay the biotin

None of them seem easy,  either to do or understand.

2.  Half-life about 5 minutes..

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_ui
ds=7017987&dopt=Abstract

". . . . Insulin half-life in the control subjects was 5.2 +/- 0.3 min and
3.9 +/- 0.2 min in the trauma group. . . ."

Regards
 Old Al

IT is very rarely measured, most of the time you are only interested
in endogenously produced insulin anyway. Insulin starts life as
proinsulin, it splits into two parts, insulin and peptide-C. Because
peptide-C and insulin have similar serum half life, Peptide-C is
universally used as a surrogate for insulin.

Insulin levels could probably be measured the same way C-peptide is,
Radio-Immuno-Assay (RIA), although that may not measure anything
except human insulin (depends upon where the antibody attaches). The
levels are sufficiently low that you need to resort to fairly subtle
techniques to measure it.

Not very long, on the order of 15 minutes, hence the question about
the kidneys not removing insulin is suspect. Insulin usually doesn't
stick around long enough to be removed.

We have had a posting that the half-life of insulin in
the blood stream is 9 minutes.  This is why it is
injected into fatty tissue to seep into the blood stream.

Hello Guy,

We measure insulin levels in our office.

Our particular method is based on "chemiluminescence". The manufacturer has
developed an antibody specific for the insulin molecule. The antibody has
incorporated into it a side chain that fluoresces under certain wavelengths.

So we simply load a small sample of blood into our analyzer, it is mixed
with the chemiluminescent reagents, and a light reading is measured a few
minutes later.

The results are very reproducible, and we have never score less than 100% on
our lab proficiency tests.

We can also test for c-peptide, but that is reserved for special situations.

Insulin levels are more commonly used in day to day testing; for instance in
order to estimate insulin resistance (by HOMA calculations) or to verify
Medicare eligibility for an insulin pump.

The half life of insulin depends upon renal function. Insulin is cleared by
the kidneys. With normal renal function the half life is only 5 - 9 minutes,
and much longer (hours) for those with renal impairment.

But you need to be careful here.

The biological activity is longer, as there are residual insulin molecules
sitting on insulin receptors for much longer.

This is the difference in pharmacoKINETICS vs. pharmacoDYNAMICS.

The pharmacodynamic effect of insulin is much longer than 9 minutes.

Back in the "old days" we would give 100 unit intravenous doses of insulin
every hour for DKA. This would saturate the insulin receptors, giving us
maximum effect in clearing DKA. With the advent of the IVAC pump, we don't
need to do this anymore.

Cheers,
William C Biggs MD

Cheers