Albumin is a test included in the (usually yearly) Comprehensive Metabolic Panel (CMP). It’s the most abundant protein in the blood stream, made in the liver at the high rate of 10-15 grams per day.
Here’s what it does.
Albumin and Blood Volume
First, a quick lesson in osmosis. In any given closed environment, any system will tend toward equilibrium, or balance. What this means: say you have two fluids, one highly concentrated salt water and the other is very dilute salt water, separated by a membrane only permeable to water. What will happen is, the water in the less concentrated solution flow into the more highly concentrated salt water until both sides are equal in terms of their concentration of salt (even though one will end up with a much higher volume than the other side). That’s osmosis.
In the bloodstream, the main solute (or component of the blood) that regulates this process is albumin. This is because it’s a big molecule, so it doesn’t flow out into the tissues easily. Instead, it tends to draw water in to the blood vessels, which helps the blood pressure to remain stable. It’s also because albumin is negatively charged, and water is polar (meaning one end of the molecule is positive and the other end is negatively charged). This, too, will attract water into the bloodstream, because the negatively charged albumin will attract the positive end of the water molecule.
Albumin as a Delivery System
Albumin is also a major transporter of smaller molecules from point A to point B in the body. This, too, is because it’s negatively charged, and so it can attract various other polar or positively charged molecules. Albumin can thus serve as a carrier for vitamins, enzymes, hormones, bilirubin, free ions (positively charged), and fatty acids, as well as for various pharmaceuticals.
Because of this latter function, significantly low albumin levels (see below) can mean more unbound drugs, which can increase sensitivity to the drug in question.
What Low Levels Mean
Low levels of albumin are significantly more concerning than high levels, and there are quite a few more possible causes.
The first possible concern with low levels is a poorly functioning liver. This is because albumin is made in the liver. If the liver is compromised, it won’t perform its various functions well, and levels will be inadequate.
The second is that the kidneys might be damaged. The kidneys should reabsorb anything that shouldn’t be urinated out. If they’re not doing their job properly, albumin might spill into the urine, leaving too little in the bloodstream.
Another possibility is that the albumin is somewhere other than in the bloodstream. It’s normal for some of it to leak out into the lymph and interstitial tissues (the spaces between cells), but if too much of it does that, it becomes edema, or ascites (depending upon where the excess fluid is located in the body). This is usually symptomatic of another, possibly severe condition.
Any inflammatory condition can present with low albumin levels as well. This study speculates that this has to do with decreased albumin mRNA made in the liver, leading to less albumin made and more of it getting broken down. (I would assume, if this mechanism is correct, that it implies liver compromise under inflammatory conditions, which might make sense from the standpoint of oxidative stress.)
There’s some speculation that malnutrition can cause low albumin; while it’s true that fasting can drop albumin production within 24-48 hrs, it will resume at normal levels within 15-30 minutes of eating again. Furthermore, this study states that only rare nutritional conditions can cause low albumin. It’s thus not generally a good marker of nutritional status.
What High Levels Mean
High albumin generally just means fluid loss, one way or the other—dehydration, or dehydration secondary to something like vomiting or diarrhea. This is because any sort of fluid loss will increase the relative concentration of other solutes in the blood, and albumin is a big one.
There are certain medications that can increase albumin levels too.
(I’ve recently noticed that major labs have shifted the upper limit of the albumin reference range lower, too. Thus, what was considered “normal” before, suddenly isn’t. Reference ranges vary by the lab, and they’re just based on a bell curve of values for a given test for the population. Because of this, reference ranges aren’t always indicative of optimal levels for health.)