The nucleated red blood cell (NRBC) count may be increased at birth in an infant with intrauterine fetal asphyxia. If a cord blood sample was not analyzed, an estimate of the number of NRBC present at birth can be made based on the number of seen within histologic sections of the placenta. The authors are from the University of Rochester, Toledo Children's Hospital and Medical College of Ohio.



(1) Count the number of nucleated red blood cells in a given volume of blood within a large placental blood vessel.

(2) Convert the count to NRBC in 10^9/L.

(3) Estimate the NRBC count in the fetal blood based on the placental count. This is done using a linear regression equation comparing placental and cord blood counts.


The volume for counting is determined by a counting square, grid or circle. The simplest calculation is for the number of NRBC within an area delimited by a counting square.


volume in µL =

= ((side of counting square in mm)^2) * (thickness in microns) =

= ((side) ^2) * (thickness) * 0.001 cubic mm =

= ((side) ^ 2) * (thickness) * 0.001 µL


NRBC count per µL =

= (number NRBC counted in volume) / (volume in µL)


NRBC count in 10^9/L =

= (NRBC count per µL in the placenta) / 1000


LN(newborn NRBC count in 10^9/L) =

= (1.002 * LN(placental count in 10^9/L)) + 1.173 =

= X


newborn NRBC count in 10^9/L at birth =

= EXP(X)



• There are numerous sources of errors in the counts, and the correlation coefficient is mediocre (r-square 0.743). However, it can give a rough estimate of the count when no other data is available.


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