Introduction
Heparin, also known as unfractionated heparin (UFH), is a widely used
anticoagulant in medicine due to its pharmacological properties, such as
the rapid mechanism of action, simplicity of monitoring, and rapid
reversibility (1). Therefore, heparin remains ahead of other
anticoagulants in many circumstances, such as cardiac surgery and
mechanical valves, where alternatives are limited. But unfortunately,
along with its beneficial properties, it can lead to severe adverse
effects such as Heparin-induced thrombocytopenia (HIT). (2,3)
HIT is a severe and potentially fatal prothrombotic syndrome. (4,5)
Additionally, HIT frequently goes undiagnosed since thrombocytopenia is
common in hospitalized patients and can be brought on by various causes.
HIT refers to a platelet count drop within 5-10 days of receiving
heparin. There are two distinct forms of HIT. The first type (HIT type
1) is benign without an elevated risk of thrombosis; it was once known
as heparin-associated thrombocytopenia. The second form is type 2, which
usually occurs due to an immunological reaction to heparin-platelet
factor 4 antibody complexes (2,6). The reaction results in platelet
activation, the release of procoagulant platelet microparticles,
increased thrombin release, platelet consumption, and thrombocytopenia.
Therefore, thrombosis is a much more common sign of HIT than bleeding
(5,7).
Current guidelines recommend using the 4T pretest probability scoring
system (Table 1) if HIT is suspected. This is then used to guide testing
and treatment. If the score is intermediate to high, PF4 testing is
performed. If positive, the diagnosis is confirmed through an ELISA test
or serotonin release assay (SRA). If the PF4 is negative, HIT is ruled
out. When the diagnosis of HIT is intermediate or high in probability
and leads to serological testing, all forms of heparin should be
discontinued (8,9,10). However, anticoagulation can be continued with
non-heparin anticoagulation, such as danaparoid, lepirudin, or
argatroban. (10,11)
A low score on the 4T would result in a < 1% pretest
probability. In this case, further testing is not recommended in most
cases. This has led to an absolute reliance on the 4Ts to guard against
PF4 testing in several hospital settings. In some circumstances, the
provider must input patient data and obtain the score before being
allowed to test.
Are guidelines infallible or absolute? What happens when Physicians are
guided to rely solely on policies and forget about their clinical
judgment?
In this article, we report an interesting case of HIT thrombosis without
thrombocytopenia, and with a low pretest probability that led to delayed
testing and treatment. We aim to raise awareness of not relying blindly
on guidelines but using them and therapeutic guides and tools to aid in
our clinical diagnosis and treatment of patients.