Which of the following statement(s) concerning laboratory studies used in monitoring a patient with intravenous heparinization is/are correct?

c. The activated partial thromboplastin time (aPTT) should be maintained at approximately 1.5 times normal

In monitoring the effect of heparin, an activated partial thromboplastin time (aPTT) of 1.5 control or a thrombin clotting time (TCT) of 2 times control reflects adequate anticoagulation. The prothrombin time remains normal. Heparin-associated thrombocytopenia from an immune mechanism is a potential complication of the use of this anticoagulant. Therefore any patient undergoing heparin therapy should have a platelet count determined every other day after the fourth day of therapy or earlier if he or she is known to have been exposed to heparin in the past. Heparin is not excreted through the kidneys or the liver but is cleared through the reticuloendothelial system. Therefore the dose of heparin need not be adjusted in cases of liver or renal dysfunction.