I am a very light smoker. (2-3 tokes a couple times a week for 2 weeks
in a row then 2 weeks off with nothing to smoke)I weigh about 200 lbs
and have an average metabolism. I am about 25 lbs overweight for my
height (6'0) I get very good exercise 3 days a week and am active most
of the rest of the week. I recently took a drug screening (urine
test)It had been 11 days since my last smoke. When i got home after
the screening I took a fairly big toke. I remembered a home test that
I had not opened yet. I figured if I acted quick enough I could get an
accurate reading without the toke affecting it. It took about five
minutes since I smoked. My home test came up positive so I naturally
assumed my screening will come up positive. I took another home test 3
days later and it was negative. My positive home test was 1 year old
but still in an unopened package. My question is this: If I had about
3-4 tokes 11 days ago and I test positive on a home test how could I
test negative 3 days later after doing a new toke and could the new
toke affect my test after just 3-4 minutes in my bloodstream?

It all depends on what you mean by "toke".  Was it is a small, medium
or large toke? If the oranges are all lined up there shouldn't be any
apples in between the oranges.  The THC content of the smoke could
also be a factor.  Toke, smoke, job, they all end in "e".

large tokes held in

large toke held in

First of all, English is not my first language so apologize if I make mistakes...

2 explanations:

1)
I don't know the kind of test you used at home but the test we use in
hospitals are very very sensible (and I think that home tests are now
almost as sensibles). We can detect up to 20 ng/ml and sometimes 15
ng/ml. Since THC (11-carboxy-THC is the exact element we test) binds
to seric proteins at a level of 97%, you'll have a THC concentration
very fast in your blood. Your blood is then filtered by your kidneys.
If you're renal function is good enough, you are able to filter
100-200 ml/min of blood. After 5 minutes, you filtered almost 1
liter... You'll not have 1 liter of urine but 1 liter of liquid will
have been filtered and a part of it detoxified by concentrating the
THC in your bladder. I say again, if you are young and have a normal
kidney function. 5 minutes is enough to test positive...

2) You say by yourself that you are about 25 lbs overweight. THC is
very lipophilic. Those kind of test can come back positive up to 6
weeks after the last "toke" because of THC stored in fat. However,
it'll stay in your fat as long that you don't burn that fat. Suppose
that you smoke, then you do no sport at all for 3 days, the test may
be negative three days later if you have a very good renal function
and you take a small quantity of marijuana at first (half-life of THC
is between 20-40 hours). BUT, if on the fith day you do intense
physical exercise, you'll release in your blood stored THC already in
your fat and you can have a positive test even if you did not smoke in
a week. This phenomenom is even more true if you are a regular smoker
(you say you don't smoke a lot but you do smoke regurlarly, wich is
enough to have a lot of THC stored in your fat, or at least, enough
for our test to detect).

So, in summary, yes, a "toke" could affect your test few minutes only
after taking it. Your test can also come positive after days or weeks
without taking any drug because of your body fat and depending on the
fat burning process occuring in your body.

If you have some other questions, ask, I'll be glad to answer!

Hope this helps

From a last year medical student (MD in 2 months! yeah!)