It is commonly known that the period between 1935 and 1953 represents the so-called golden age of coagulation discoveries (e.g., 1936 discovery of FVIII, 1947 discovery of FV, 1951 discovery of FVII, 1936 discovery of FVIII, 1952 discovery of FIX, and 1953 discovery of FXI). In 1953, Langdell and collaborators described for the first time the partial thromboplastin time in a hemophilic patient. They modified the laboratory purification method to obtain thromboplastin using only a “partial” form that today is known to consist exclusively of phospholipids. Indeed, the PT was not altered in the plasma of hemophilic subjects. Instead, the use of a partial thromboplastin (without tissue factor) allowed us to easily distinguish hemophilic from nonhemophilic subjects. The aPTT is performed on a sample of citrated plasma, recalcified with calcium chloride, to which phospholipids and an activating agent are added. Indeed, to make aPTT more reproducible, in 1961, Rapaport introduced the use of kaolin (an activator) capable of activating FXII, which represents the starting point of the intrinsic pathway. Today, in addition to kaolin, ellagic acid, and silica crystals are also used.
The aPTT is expressed as the ratio between the time, expressed in seconds, of the patient and an average time obtained from a sample of subjects not affected by coagulation alteration or in therapy with anticoagulant drugs, according to the following relationship:
aPTT = aPTTpatient (s) / aPTTplasma pool
The aPTT allows evaluation of the most common facto rial deficiencies of the intrinsic and common pathways (especially FXII, FVIII, and FIX). Moreover, the observations of Conley and Hartmann first and then of Bowie led to the evidence that the elongation of the aPTT was due to the presence of the so-called lupicanticoagulant (LAC). The different commercial reagents have different sensitivitin recognizing the presence of LAC, and, therefore, specific aPTT (aPTT-LA) have been developed to recognize the presence of these antibodies that can lead to thrombotic situations. The aPTT is, therefore, a very versatile test that has found wide use in the clinical laboratory for the assessment of both hemorrhagic and thrombotic risk.
