Be reassured, you can
vape all you like: Nicotine is
not what causes the elevated hemoglobin levels. It's the
carbon monoxide from cigarettes: see
this abstract here from the Journal of the American Medical Association. Quoted:
Anemia is a condition of inadequate hemoglobin, due either to defects in hemoglobin formation or a reduced number of red blood cells. Cigarette smoking is known to cause an increase in the level of hemoglobin, apparently as a response to the tight chemical bond that becomes established between carbon monoxide (a by-product of tobacco smoking) and hemoglobin.
Sadly, this effect (along with the extra energy from nicotine) is probably what has been masking my ferritin(iron)-deficiency anemia for a
long time now...I am just discovering this.

(I would especially encourage young women who are vaping to get their ferritin levels and red blood counts checked when they have stopped analogs, especially if they have any symptoms associated with anemia.)
See
this abstract for the explanation:
Among women, smokers had a mean (±SE) hemoglobin level of 137 ±0.4 g/L, significantly higher than the mean hemoglobin level of 133 ±0.5 g/L for never-smokers. Among men, the mean hemoglobin levels for smokers and never-smokers were 156 ±0.4 and 152 ±0.5 g/L, respectively. No significant difference in mean hemoglobin was noted between ex-smokers and never-smokers. Mean hemoglobin levels and carboxyhemoglobin levels increased progressively with the number of cigarettes consumed per day. Cigarette smoking seems to cause a generalized upward shift of the hemoglobin distribution curve, which reduces the utility of hemoglobin level to detect anemia. Among women of comparable socioeconomic status, the prevalence of anemia was 4.8% ±0.6% among smokers, compared with 8.5% ± 1.2% among never-smokers. This study suggests that minimum hemoglobin cutoff values should be adjusted for smokers to compensate for the masking effect of smoking on the detection of anemia.
(They don't use "ex smokers" in these studies, because it can be so variable (how long has it been since quitting, how much did you use, etc.) They usually compare "never-smokers" with "current smokers".)
Back to the original poster's question:
So
it's not nicotine. If you start vaping 100% of the time, your hemoglobin will return to normal.
How long would this change take...?
According to the
CDC's tox profile on carbon monoxide, it takes about a
day for your body to rid itself of carbon monoxide. That's
acute exposure, though,
not chronic like us smokers have had.
In chronic years of exposure,
you've built it up in your blood, it's bound to a lot of hemoglobin, and it will take time for your body to replace that.
So on the other end of the time-spectrum, there is this paper (which is gated so I can't link to an abstract):
Quitting Smoking May Restore Hematological Characteristics within Five Years, Annals of Epidemiology, Volume 12, Issue 6, Pages 378-388, E.Van Tiel
These kinds of studies usually measure levels at year or multi-year intervals. Five years is probably the outer limit for
all blood levels to restore to normal in almost all people.
In between those two (one day vs. five years) where do you probably stand???
How long will it take on average for you to replace all your hemoglobin with healthy, carbon-monoxide-free normal-level hemoglobin? (I am
not a scientist or a doctor, this is a totally back-of-the-envelope type thing.) Well, based on blood-donation schedule estimates, it takes about 36 days for the average male to replace 500 ml of red blood cells (produced by the bone marrow). (The range is wide, between 20 and 59 days.) The average 70 kg/154 lb man would have ~5.5 liters of blood. To replace all of the blood in your body entirely then would take about
1.08 years on average, with a range of eight months to two years.
My guesstimate? An ex-chronic smoker will probably get back within normal range
within a year,
plus or minus a lot of individual variation based on how much and how long one has smoked.
Unfortunately, I
wouldn't expect a week to make a huge difference, especially if you're still smoking. (But do report back and I hope I'm proven wrong!)
whew.
i loves the medical internets.