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What are TNC, MNC, CD34+, and CFU, and why should I care?

These are all ways of counting cell types, and they tell you whether or not your cord blood collection has lots of stem cells and if they are healthy.

Stem cells happen to be Mono-Nuclear Cells or MNC: when you look at them under a microscope there is only one nucleus.  Unfortunately, one of the most difficult aspects of stem cell biology is that you can't identify a stem cell just by looking at it.  There are other types of blood cells which are also MNC, such as nucleated red blood cells.  The only proof that a cell is a stem cell comes from how it behaves when it multiplies. 

Scientists have worked for years to develop various chemical stains which have a high affinity for stem cells.  The best known marker for blood-forming stem cells is that they test positive for CD34, a protein found on the surface of stem cells.  But, CD34+ counts are not an accurate measure of stem cells: CD34+ results vary between labs, they can vary within a single lab, and only 1-2% of the MNC that have CD34+ are actually stem cells.

The Total Nucleated Cell count or TNC is the test most often reported as a measure of the cell count after cord blood processing. The main advantage of measuring TNC is that the count is highly reproducible within and among labs, so it can be used accurately throughout the blood banking community.  Even better, the TNC count can be automated with the use of a device called a flow cytometer.

At present Colony Forming Units or CFU are considered to be the best measure of whether stem cells are "viable", or quite frankly alive. Unlike the TNC count, which  includes both living and dead cells, the CFU test only reads living cells. The CFU  test is run by taking a small portion of the cord blood and watching it under controlled conditions to see if stem cells divide and form colonies. This used to be a subjective measure, performed by a human with a microscope,, but in recent years it has been standardized with technology to image the cells and count colonies in the image. The only practical problem with this test is that it takes a week for colonies to grow. If the CFU test reads "zero", it means the cord blood does not contain living cells and is not worth banking