It is necessary to reduce the amount of anticoagulant (0.129 M = 3.8% sodium citrate) used in specimens for coagulation testing, when the hematocrit is elevated above the normal adult values. With higher hematocrits, less plasma is present; if not reduced, the relative amount of anticoagulant is increased and prolongs the clotting time.
Elevated hematocrits requiring the adjustment are seen in newborns and in patients with polycythemia.
NCCLS recommends the following equation:
volume of anticoagulant required to prepare 1 mL of anticoagulated blood =
= (100 - (hematocrit)) / (595 - (hematocrit))
where:
• The hematocrit is given as a whole number and not the percent.
Hathaway and Goodnight give the following table:
Hematocrit (in percent)
Amount of Anticoagulant for 1 mL Anticoagulated Blood (End Product)
70
0.06
60
0.075
50
0.09
40
0.10
A line fitted to this data is:
amount of anticoagulant for 1 mL anticoagulated blood =
= ((-0.00135) * (hematocrit)) + 0.1555
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