Summary
Patients with a shortened activated partial thromboplastin time (APTT) of less than
29 sec (≥2.5 SD below the mean) were followed for the development of peripheral deep
vein thrombosis by clinical findings. Perfusion lung scans were performed in patients
with clinical symptoms suggesting pulmonary embolism. 23 of 100 patients in this prospective
study developed thrombo-embolism (TE). This represents a tenfold increase over the
overall incidence of 2.2% in medical and surgical patients during the study period.
Shortened APTT’s were encountered most commonly in patients with disseminated malignancy
and in surgical patients. Post-op er ative patients with an APTT of ≤ 28 sec were
at high risk for the subsequent development of TE (43 %). There was a correlation
between frequency of shortened APTT, degree of shortening of the APTT and incidence
of TE. Patients with APTT’s of ≤ 28 sec on at least three occasions or ≤ 25 sec on
at least one occasion had a 53% incidence of TE. Prophylactic low dose heparin therapy
is therefore recommended for all patients who show a persistent mild shortening of
the APTT or a severe shortening of the APTT on at least one occasion during periods
of high risk, e.g. during immobolization or after surgery.