Chong and Chong developed a scoring system for the diagnosis of heparin-induced thrombocytopenia (HIT). This can help identify a patient who should be anticoagulated with a non-heparin agent. The authors are from St George Hospital, in Kogarah, New South Wales in Australia.
Patient selection: Thrombocytopenia in a patient exposed to heparin (mandatory). Thrombocytopenia is defined as one of the following:
(1) platelet count < 150,000 per µL, OR
(2) > 50% decline from baseline
Parameters:
(1) onset of thrombocytopenia
(2) exclusion of other causes of thrombocytopenia
(3) resolution on discontinuing heparin
(4) recurrence on heparin rechallenge
(5) thrombosis
(6) laboratory testing
|
Parameter |
Finding |
Points |
|
onset of thrombocytopenia after starting heparin |
starting 4-14 days |
3 |
|
|
< 4 or > 14 days |
1 |
|
exclusion of other causes |
yes |
2 |
|
|
no |
0 |
|
resolution on discontinuing heparin |
yes |
2 |
|
|
no |
0 |
|
recurrence on rechallenge |
yes |
1 |
|
|
no |
0 |
|
thrombosis |
present |
1 |
|
|
absent |
0 |
|
laboratory testing |
immunoassay positive |
2 |
|
|
2-point functional assay positive |
3 |
|
|
non-2-point functional assay positive |
2 |
|
|
assays negative |
0 |
where:
• I thought that HIT could appear quickly (less than 4 days) if the patient had a previous episode recently.
• I am assuming that only 1 laboratory test result is scored.
• A 2 point functional assay refers to a positive test when heparin is present at a therapeutic level but negative at 100 U/mL (high level). Excess heparin characteristically interferes with the antibody reaction in HIT (page 549).
total score =
= SUM(points for all 6 parameters)
Interpretation:
• minimum score: 1
• maximum score: 12
• The higher the score the more likely HIT is present.
|
Total Score |
Interpretation |
|
1 or 2 |
unlikely |
|
3 or 4 |
possible |
|
5 or 6 |
probable |
|
7 to 12 |
definite |
Specialty: Hematology Oncology, Clinical Laboratory, Pharmacology, clinical, Critical Care, Immunology/Rheumatology
