Serum vs Intracellular Nutritional Testing: There is a Difference

Serum vs Intracellular Nutritional Testing: There is a Difference

January 15, 2021

What is serum testing?

A serum test is simply a laboratory test that detects something in the liquid (which would essentially be the plasma) part of blood, as opposed to a laboratory test that detects something in the solid part (which would be the red and white blood cells) of the blood.

Since blood is made of both cells and plasma, the term “blood test” is not very specific, as it could refer to either. However, the term “serum test” is specific – it means something measured outside the cells (extracellular) in the plasma portion of blood.

For the purposes of micronutrient testing, serum testing is practically synonymous with plasma testing. (Serum + clotting proteins = Plasma). In both cases, measuring a micronutrient in serum means you are measuring the micronutrient level in the liquid portion of the blood, i.e. the portion of the blood that does not contain cells. Blood serum does contain nutrients, hormones and proteins – but measuring these items in serum means they are extracellular – their levels are being measured outside the actual cells.

What is intracellular testing?

An intracellular blood test is a laboratory test that measures something inside a red or white blood cells, as opposed to measuring something in the liquid surrounding the blood cells in which they are essentially floating. In the case of SpectraCell’s Micronutrient test, it measures nutrient status in white blood cells (peripheral T-lymphocytes).

Why is it important to measure nutrients inside the cells instead of just in the blood serum?

The reason is that all metabolism happens inside the cell. Metabolism does NOT happen in the liquid plasma outside the cell. This means every biochemical reaction needed to sustain life – like energy production, cellular repair, detoxification, growth, protein synthesis, genetic expression – all these functions occur inside the cell. Measuring nutrient levels outside the cell tells you nothing about what is going on intracellularly — where it matters.

Imagine you have a car that has a full gas tank. The gas gauge says FULL. But for whatever reason – perhaps the fuel line is broken – that fuel is not reaching the engine. Your car will not function. Your cells are like that engine. It doesn’t matter if there is gas in the tank (or nutrients in the serum) if that gas cannot get to the engine (inside the cell), it won’t drive. If nutrients don’t get inside the cell, metabolic function doesn’t happen.

Can I have high serum but low intracellular micronutrient status?

Yes, in fact, this is common. There are many reasons that a nutrient may be low inside the cell:

  • Poor transport of nutrients across the cell membrane
  • Cofactors needed to utilize the nutrient are missing or low
  • Malabsorption of nutrients into cells
  • Circadian rhythms alter serum levels but not intracellular levels
  • Serum levels fluctuate with recent supplement or food intake 

Functional deficiencies often exist when serum levels are “normal.”


Is intracellular testing the same as functional testing?

Not necessarily. Intracellular testing of micronutrients simply means that micronutrient status is being measured inside the cell wall (versus outside the cell in the blood serum).  However, measuring the mass (quantity) of a nutrient in a cell is different than measuring the function (quality) of a nutrient within a cell. It doesn’t matter how much of a vitamin exists in or out of the cell, if that cell is incapable of utilizing that nutrient. Ideally, micronutrient status should be assessed both intracellularly and functionally

Measuring levels instead of function would be akin to measuring the amount of fuel in the engine (cell) and discovering the car still won’t drive (function) because it didn’t need gas, it needed oil. Gasoline levels would be fine in the engine, but the engine still won’t function if gas is not what it needs. SpectraCell’s Micronutrient Test is both intracellular and functional


If serum testing is less useful, why is it so commonly used?

The simple reason is that serum testing has been around for decades, is widely available, easy to perform, and very inexpensive. A serum test can be run in any hospital or national laboratory because it is a commodity, non-specialty type of blood test. As far back as the 1970s, medical literature demonstrated that serum tests will miss functional deficiencies and that intracellular nutrient function is more clinically reliable than serum, but the relative cost and availability of serum testing obscured the clinical superiority of functional testing.

Serum testing may still appear cheaper, even though functional nutrient testing is more clinically informative. But for those who really delve into the research, the notion of serum testing of nutrients being less useful (at best) and misleading (at worst), is highly substantiated.

In summary, not all laboratory testing is created equal, and understanding the difference, can have a profound impact on your health. 

Discover why SpectraCell's Micronutrient has been chosen by over a million patients worldwide. 

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Diet and Nutrients , Dietary Supplements, Blog