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CBC and PTH Tubes
Arthur Rosenthal, Ph.D
Nationwide Laboratories strongly recommends the use of two 2-mL light lavender tubes, Becton-Dickinson no.36-7841 instead of one 4-mL dark lavender tube (BD 36-7861), when both CBC (or H&H) and intact PTH I intact Osteocalcin tests are ordered. No more blood is involved in carrying out this new recommendation, but a number of advantages accrue.
By spreading out the blood collection between two separate specimens, the PTH I osteocalcin tests, which are long procedures, can be started earlier, which will tend to improve turnaround time.
The CBC specimens are mixed slightly more rapidly in the lower-volume tube, since there is more mixing space.
No additional blood is required for Hemoglobin A1C or Reticulocyte tests, which can still be taken from the CBC tube.
It should be noted that both the 2-mL and 4-mL tubes have the same external dimensions, but the 2-mL tube has half the vacuum and half the EDTA. They will fill up only to about one-third the total volume of the tube (Instead of the two-thirds seen in the 4-mL tube). This is normal and does not signify any defect in the draw.
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