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Thrombocytopenia (or -paenia, or thrombopenia in short) is the presence of relatively few platelets in blood. more...

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Generally speaking a normal platelet count ranges from 150,000 and 450,000 per mm3. These limits, however, are determined by the 2.5th lower and upper percentile, and a deviation does not necessary imply any form of disease.

Signs and symptoms

Often, low platelet levels do not lead to clinical problems; rather, they are picked up on a routine full blood count. Occasionally, there may be bruising, nosebleeds and/or bleeding gums.

It is vital that a full medical history is elicited, to ensure the low platelet count is not due to a secondary process. It is also important to ensure that the other blood cell types red blood cells, and white blood cells, are not also suppressed.


Laboratory tests might include: full blood count, liver enzymes, renal function, vitamin B12 levels, folic acid levels, erythrocyte sedimentation rate.

If the cause for the low platelet count remains unclear, bone marrow biopsy is often undertaken, to differentiate whether the low platelet count is due to decreased production or peripheral destruction.


Decreased platelet counts can be due to a number of disease processes:

  • decreased production
    • vitamin B12 or folic acid deficiency
    • leukemia or myelodysplastic syndrome
  • peripheral destruction
    • immune thrombocytopenic purpura (ITP)
    • thrombotic thrombocytopenic purpura (TTP)
    • hemolytic-uremic syndrome (HUS)
    • disseminated intravascular coagulation (DIC)
    • paroxysmal nocturnal hemoglobinuria
    • antiphospholipid syndrome
    • medication-induced:
      • Many of the commonly used drugs may cause thrombocytopenia or low platelet counts. Some drugs like anticancer drugs and valproic acid causes thrombocytopenia in a dose depended mechanism by causing myelosuppression. Some other groups of drugs cause thrombocytopenia by immunological mechanisms. Based up on the mechanism immunological drug induced can be caused by two types.
      • Example of the first mechanism is the quinidine group of drugs. This is caused by drug depended binding of Fab part of the pathological antibody with the platelets, causing the destruction of platelets.. Fc portion of the antibody molecule is not involved in the binding process.
      • Example of the second mechanism is heparin induced thrombocytopenia (HIT). In this type the Fab portion of the pathological antibody binds to platelet factor 4 (PF4).When complexed with heparin or other drugs, the Fc portion of the antibody molecule bind to platelet receptors causing platelet activation. Since Fc portion of the antibody is bound to the platelets, they are not available to the Fc receptors of the reticulo-endothelial cells. This may explain, why severe thrombocytopenia not commonly seen in patients with HIT.
      • A full list of known drugs causing thrombocytopenia is available at the linked website. Most of the elderly patients are on multiple medications and the intake of these drugs must always be considered in the differential diagnosis of thrombocytopenia.
      • heparin-induced thrombocytopenia (HIT or white clot syndrome): this is a rare but serious condition that may occur in a hospitalized population especially in the cardiac units where they are exposed to large quantities of heparin. HIT may occur with a delay of 4 to 14 days after exposure to heparin. As mentioned above the heparin-PF4 antibody complex will activate the platelets, and this will lead to clotting. A term known as paradoxical thrombosis (HITT, where the last T is for thrombosis) is often used to describe this condition.
      • abciximab-induced thrombocytopenia

In some tropical countries, dengue infection is a known rather common cause of thrombocytopenia associated with fever.


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Heparin-induced skin lesions and other unusual sequelae of the heparin-induced thrombocytopenia syndrome : a nested cohort study
From CHEST, 5/1/05 by Theodore E. Warkentin

Background: Heparin-induced thrombocytopenia (HIT) is caused by platelet-activating, heparin-dependent IgG antibodies (HIT-IgG). Although HIT is known to predispose the patient to thrombosis, the relationship between the formation of HIT-IgG and various other unusual clinical sequelae putatively linked with the HIT syndrome, such as heparin-induced skin lesions and acute anaphylactoid reactions following treatment with an IV heparin bolus, is not clear.

Methods: We used data from a clinical trial of postoperative heparin prophylaxis to compare the frequency of one or more predefined unusual clinical sequelae developing in 20 patients who formed platelet-activating HIT-IgG with 80 control patients who did not form HIT-IgG (nested cohort study). Results: Five of the 20 patients in whom HIT-IgG developed had one or more unusual clinical sequelae, compared with none of 80 control patients (25% vs 0%, respectively; odds ratio, [infinity]; 95% confidence interval, 4.3 to 0% p < 0.001). The unusual complications included heparin-induced erythematous or necrotic skin lesions (n = 4), an anaphylactoid reaction following IV heparin bolus use (n = 1), and warfarin-associated venous limb ischemia (n = 1). Thrombocytopenia, as it is conventionally defined (ie, platelet count fall to < 150 x [10.sup.9] cells/L) developed in only one of these five patients.

Conclusions: Certain unusual clinical sequelae, such as heparin-induced skin lesions, are strongly associated with the formation of HIT-IgG and should be considered as manifestations of the HIT syndrome, even in the absence of thrombocytopenia as conventionally defined.

Key words: anaphylactoid reaction; heparin; IgG; skin lesions; thrombocytopenia

Abbreviations: DVT = deep-vein thrombosis; HIT-IgG = heparin-induced thrombocytopenia IgG antibodies; HIT = heparin-induced thrombocytopenia; LMWH = low-molecular-weight heparin; PF4 = platelet factor 4; UFH = unfractionated heparin


Heparin-induced thrombocytopenia (HIT) is an Ig-mediated adverse drug reaction characterized by an increased risk for venous and arterial thrombosis. (1,2) There is anecdotal evidence that some patients with HIT can experience other unusual clinical events, including skin lesions at heparin injection sites, (3-5) acute anaphylactoid reactions following IV bolus administration of heparin, (5-7) adrenal hemorrhagic infarction, (8,9) warfarin-associated venous limb ischemia or gangrene, (10-12) "classic" warfarin-associated (central) skin necrosis, (11-14) and transient global amnesia. (15) Since thrombocytopenia, as conventionally defined (ie, platelet count fall to < 150 x [10.sup.9] cells/L), did not develop in some of these patients, the association of these clinical events with the HIT syndrome has been uncertain. (3,4)

Previously, we performed a large clinical trial in which patients undergoing elective hip replacement surgery were randomized to receive either unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH) for the treatment of deep-vein thrombosis (DVT) prophylaxis. (16-18) We performed a systematic serologic investigation for the presence of heparin-dependent IgG antibodies (HIT-IgG) in a large subgroup of these patients and identified 20 patients who formed platelet-activating HIT-IgG that were detectable by both platelet activation assay (ie, platelet serotonin release assay) (19,20) and platelet factor 4 (PF4)/heparin-enzyme immunoassay. (21) We observed a strong association between serologically confirmed HIT and thrombosis in this study. (17,18) We also found that some patients who form HIT-IgG experience a fall in platelet count of > 50% without developing thrombocytopenia (defined conventionally as a platelet count fall to below < 150 x [10.sup.9] cells/L). (18)

We now report our investigation into whether these various unusual sequelae of heparin exposure are associated with the formation of HIT-IgG. We used a nested ease-control study design, in which we compared the 20 patients who formed HIT-IgG with 80 randomly selected patients who did not form HIT-IgG. Our study suggests that the spectrum of complications of the HIT syndrome is greater than is widely appreciated, even in the absence of thrombocytopenia as conventionally defined.


Clinical Trial

Analysis was performed using data from a clinical trial of UFH and LMWH (16,17) that was approved by the institutional review board, and for which all participating patients provided written informed consent. In brief, the clinical trial compared the use of a UFH preparation (Calciparin; Anglo French Drug Company; Montreal, QC, Canada) [7,500 U subcutaneously twice daily] with the LMWH preparation enoxaparin (Lovenox; Rhone-Poulenc Borer; Montreal, QC, Canada) [30 mg subcutaneously twice daily], both beginning on the first postoperative day.

Assay for Platelet-Activating HIT-IgG

The platelet [sup.14]C-serotonin release assay and the PF4/lieparinenzyme immunoassay were used to detect HIT-IgG, as described. (19-21) For 362 patients, serial plasma samples were available in which at least one of the plasma samples was obtained on postoperative day 7 or later. Plasma samples that gave the following reaction pattern were considered to be strongly positive for platelet-activating HIT-IgG: > 50% release at 0.1 U/mL heparin; < 20% release at 100 U/mL heparin; < 20% release at 0.1 U/mL heparin in the presence of an Fc receptor blocking the monoclonal antibody IV.3; and a positive test result for anti-PF4/ heparin antibodies of IgG class (optical density, > 0.45 absorbance units). For all patients who tested positive, HIT-IgG seroconversion was proven by comparative testing with the baseline (preoperative) specimen.

Nested Cohort Study

As 20 of the 362 patients in the subgroup tested positive for HIT-IgG using the criteria defined above, we used a nested ease-control (1:4) design, thus designating for detailed chart review 100 patient records, for the 20 patients who tested positive, and 80 randomly selected patients (using a random number table) who tested negative for HIT-IgG with both the platelet activation assay and the anti-PF4/heparin-enzyme immunoassay. All medical and nursing records were reviewed in detail by study personnel who had been blinded to the results of both HIT-IgG assays and platelet counts, using specially prepared data collection sheets that listed the criteria for the following putative sequelae of the HIT syndrome (6): (1) heparin-induced skin lesions, defined (4) as painful or pruritic inflammatory (erythematous) or necrotic lesions localized to the sites of study drug injections that began on day 5 or later of UFH or LMWH use; (2) acute anaphylactoid reactions beginning within 30 min of IV bolus heparin administration (6); (3) warfarin-associated venous limb ischemia or gangrene, defined as acral (distal extremity) ischemia or necrosis despite palpable arterial pulses in a patient receiving warfarin (10-12); (4) "classic" warfarin-induced (central) skin necrosis, defined as nonacral necrosis of dermal and subcutaneous tissues in a patient receiving warfarin (22); (5) adrenal hemorrhagic infarction (compatible clinical picture of abdominal or flank pain and/or hypotension, confirmed by radiologic imaging); (6) transient global amnesia (15); and (7) "resistance" to the anticoagulant effect of therapeutic-dose UFH, defined as the requirement for > 35,000 U of heparin per 24 h to maintain a therapeutic activated partial thromboplastin time. (23)

Statistical Analysis

We compared the proportions of patients who had outcome events between groups by Fisher exact test (24) and an associated method by Gart (25) for computing confidence intervals around the odds ratio. All quoted p values are two-tailed.


Inflammatory skin lesions (n = 3) or necrotic skin lesions (n = 1) at heparin injection sites were more likely to have developed in patients with test results that were positive for HIT-IgG, compared with patients in whom HIT-IgG did not develop (4 of 20 vs 0 of 80 patients, respectively; p < 0.001) [Table 1]. These lesions all began on postoperative day 7 or later. The patient in whom necrosis developed at the heparin injection sites had mesenteric artery thrombosis complicating an 81% fall in the platelet count from 401 to 75 x [10.sup.9] cells/L, but heparin therapy was later restarted as the thrombocytopenia had been attributed to the effects of bowel infarction rather than to HIT (which was not proven serologically until after the patient's discharge from the hospital). Thrombotic events did not occur in the remaining three patients in whom nonnecrotizing, inflammatory, heparin-induced skin lesions developed.

A severe acute anaphylactoid reaction developed in one patient who tested positive for HIT-IgG on postoperative day 13 that began 10 min after an IV bolus administration of 5,000 U UFH (Fig 1). The reaction was characterized by chills and rigors, dyspnea, tachypnea, diaphoresis, headache, flushing, restlessness, and tachycardia, and the platelet count abruptly fell by 58% from 705 to 297 x [10.sup.9] cells/L. This patient had been noted to have inflammatory (erythematous) skin lesions at the LMWH injection sites 3 days before the UFH bolus was administered, but this had not been recognized as a possible manifestation of the HIT syndrome.

Limb ischemia, despite palpable pulses (ie, cyanotic toes and painful forefoot) in the limb affected by veno-graphically proven calf DVT during anticoagulation therapy with warfarin, developed in one patient who had tested positive for platelet-activating HIT-IgG. The clinical manifestations were of sufficient severity to prompt a vascular surgical consultation. The platelet count fell by 58% from 383 to 161 x [10.sup.9] cells/L in association with this clinical event, which was judged to be a ease of warfarin-associated venous limb ischemia (ie, digital and forefoot ischemia associated with warfarin use during the treatment of HIT-associated DVT).

Adrenal hemorrhagic infarction, classic warfarin-induced skin necrosis, or transient global amnesia did not develop in any patients or control patients. Resistance to the anticoagulant effect of IV therapeutic-dose UFH was not more common among patients who formed HIT-IgG, compared with control patients treated with therapeutic-dose UFH.

Thus, 5 of the 20 patients in whom HIT-IgG formed developed six unusual sequelae putatively linked to the HIT syndrome, which was a higher percentage than that in the control population (25% vs 0%, respectively; odds ratio, 4.3 to [infinity]; p < 0.001). Thrombocytopenia, as conventionally defined, developed in only one of these five patients, although the platelet count fell by [greater than or equal to] 50% from the postoperative peak in association with HIT-IgG formation in three of the remaining four patients.


The association between thrombocytopenia and thrombosis in patients who form HIT-IgG has been recognized for > 25 years. (26) Subsequently, a number of other unusual clinical events, including heparin-induced skin lesions, (3-6) acute systemic (anaphylactoid) reactions following IV bolus heparin use, (6,7,15 and warfarin-associated peripheral limb or central skin necrosis syndromes, (10-14) among others, have been reported in association with HIT.

In this study, we capitalized on our observation that platelet-activating HIT-IgG developed in 20 of 362 patients participating in a clinical trial comparing UFH and LMWH for postoperative antithrombotic prophylaxis following elective hip replacement surgery. We performed a detailed chart review of these 20 patients, as well as of 80 randomly selected control patients who had tested negative for HIT-IgG. The reviewers were blinded to the HIT-IgG and platelet count results.

Among the 20 patients who tested positive for HIT-IgG, we identified 5 patients in whom one or more unusual clinical sequelae putatively linked to the HIT syndrome had developed. These included four patients in whom heparin-induced skin lesions developed, one patient in whom an acute anaphylactoid reaction developed following administration of an IV heparin bolus, and one patient in whom venous limb ischemia developed during the use of warfarin to treat DVT. Neither these nor any other predefined unusual complications associated with the HIT syndrome developed in any of the 80 control patients. A platelet count fall that reached thrombocytopenic levels, as conventionally defined (platelet count of < 150 x [10.sup.9] cells/L) developed in only one of the five patients who had tested positive for HIT-IgG. However, a platelet count fall of [greater than or equal to] 50% developed in four of the five patients in association with HIT-IgG formation. None of these five patients were suspected of having had HIT by the attending physicians when the clinical trial was conducted, suggesting that the infrequent occurrence of thrombocytopenia (as conventionally defined) or the unusual nature of the complicating events obscured the relationship of these clinical features with the HIT syndrome. The importance of recognizing these unusual sequelae as manifestations of the HIT syndrome was illustrated by the patient who evinced erythematous skin lesions at the sites of LMWH injection, and who subsequently received an IV bolus of UFH that resulted in an acute systemic reaction (Fig 1). Although this patient recovered without adverse longterm consequences, fatal cardiopulmonary arrest (5,6,27,28) in association with IV heparin bolus use in the setting of HIT antibodies has developed in other patients. Moreover, in recent years, several nonheparin anticoagulants, such as lepirudin and argatroban have been approved to treat patients who cannot receive UFH or LMWH because of HIT. (29) We suggest that unusual, but clinically important, sequelae of the HIT syndrome may be relatively more common than is widely recognized.

ACKNOWLEDGMENT: We thank Luba Klama for assistance with data collection.

* From the Departments of Pathology and Molecular Medicine (Dr. Warkentin), Medicine (Drs. Hirsh and Kelton), and Clinical Epidemiology and Biostatistics (Prof. Roberts), McMaster University, Hamilton, ON, Canada.

This study was supported by Rhone-Poulenc Rorer (now Sanofi-Aventis). The serologic studies described were supported by the Heart and Stroke Foundation of Ontario (grants No. T-4502 [T.E.W], No. T-5207 [T.E.W.], and No. T-4404 [J.G.K]). Neither the clinical trial sponsor nor the funding agency had any role in the analysis or interpretation of the data, or in the decision to submit the manuscript for publication.


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(2) Greinacher A. Antigen generation in heparin-associated thrombocytopenia: the nonimmunologic type and the immunologic type are closely linked in their pathogenesis. Semin Thromb Hemost 1995; 21:106-116

(3) White PW, Sadd JR, Nensel RE. Thrombotic complications of heparin therapy: including six cases of heparin-induced skin necrosis. Ann Surg 1979; 190:595-608

(4) Warkentin TE. Heparin-induced skin lesions. Br J Haematol 1996; 92:494-497

(5) Platell CFE, Tan EGC. Hypersensitivity reactions to heparin: delayed onset thrombocytopenia and necrotizing skin lesions. Aust N Z J Surg 1986; 56:621-623

(6) Warkentin TE. Clinical picture of heparin-induced thrombocytopenia. In: Warkentin TE, Greinacher A, eds. Heparin-induced thrombocytopenia. 3rd ed. New York, NY: Marcel Dekker, 2004; 53-106

(7) Popov D, Zarrabi MH, Foda H, et al. Pseudopulmonary embolism: acute respiratory distress in the syndrome of heparin-induced thrombocytopenia. Am J Kidney Dis 1997; 29:449-452

(8) Arthur CK, Grant SJB, Murray WK, et al. Heparin-associated acute adrenal insufficiency. Aust N Z J Med 1985; 15:454-455

(9) Ernest D, Fisher MM. Heparin-induced thrombocytopaenia complicated by bilateral adrenal haemorrhage. Intensive Care Med 1991; 17:238-240

(10) Warkentin TE, Elavathil LJ, Hayward CPM, et al. The pathogenesis of venous limb gangrene associated with heparin-induced thrombocytopenia. Ann Intern Med 1997; 127: 804-812

(11) Warkentin TE, Sikov WM, Lillicrap DP. Multicentric warfarin-induced skin necrosis complicating heparin-induced thrombocytopenia. Am J Hematol 1999; 62:44-48

(12) Srinivasan AF, Rice L, Bartholomew JR, et al. Warfarin-induced skin necrosis and venous limb gangrene in the setting of heparin-induced thrombocytopenia. Arch Intern Med 2004; 164:66-70

(13) Celoria GM, Steingart RH, Banson B, et al. Coumarin skin necrosis in a patient with heparin-induced thrombocytopenia: a case report. Angiology 1988; 39:915-920

(14) Gailani D, Reese EP Jr. Anticoagulant-induced skin necrosis in a patient with hereditary deficiency of protein S. Am J Hematol 1999; 60:231-236

(15) Warkentin TE, Hirte HW, Anderson DR, et al. Transient global amnesia associated with acute heparin-induced thrombocytopenia. Am J Med 1994; 97:489-491

(16) Levine MN, Hirsh J, Gent M, et al. Prevention of deep vein thrombosis after elective hip surgery: a randomized trial comparing low molecular weight heparin with standard unfractionated heparin. Ann Intern Med 1991; 114:545-551

(17) Warkentin TE, Levine MN, Hirsh J, et al. Heparin-induced thrombocytopenia in patients treated with low-molecular-weight heparin or unfractionated heparin. N Engl J Med 1995; 332:1330-1335

(18) Warkentin TE, Roberts RS, Hirsh J, et al. An improved definition of immune heparin-induced thrombocytopenia in postoperative orthopedic patients. Arch Intern Med 2003; 163:2518-2524

(19) Sheridan D, Carter C, Kelton JG. A diagnostic test for heparin-induced thrombocytopenia. Blood 1986; 67:27-30

(20) Warkentin TE, Hayward CPM, Smith CA, et al. Determinants of donor platelet variability when testing for heparin-induced thrombocytopenia. J Lab Clin Med 1992; 120:371-379

(21) Horsewood P, Warkentin TE, Hayward CPM, et al. The epitope specificity of heparin-induced thrombocytopenia. Br J Haematol 1996; 95:161-167

(22) Warkentin TE. Thrombotic complications of anticoagulant therapy. In: Colman RW, Hirsh J, Marder VJ, et al, eds. Hemostasis and thrombosis: basic principles and clinical practice. 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2000; 1371-1382

(23) Levine MN, Hirsh J, Gent M, et al. A randomized trial comparing activated thromboplastin time with heparin assay in patients with acute venous thromboembolism requiring large daily doses of heparin. Arch Intern Med 1994; 154: 49-56

(24) Matthews DE, Farewell VT. Using and understanding medical statistics. 2nd ed. New York, NY: Karger, 1988; 20-26

(25) Thomas DG. Exact confidence limits for the odds ratio in a 2 x 2 table. Appl Stat 1971; 20:105-110

(26) Rhodes GR, Dixon RH, Silver D. Heparin induced thrombocytopenia with thrombotic and hemorrhagic manifestations. Surg Gynecol Obstet 1973; 136:409-416

(27) Ansell JE, Clark WP Jr., Compton CC. Fatal reactions associated with intravenous heparin [letter]. Drug Intell Clin Pharm 1986; 20:74-75

(28) Hewitt RL, Akers DL, Leissinger CA, et al. Concurrence of anaphylaxis and acute heparin-induced thrombocytopenia in patients with heparin-induced antibodies. J Vasc Surg 1998; 28:561-565

(29) Warkentin TE, Greinacher A. Heparin-induced thrombocytopenia: recognition, treatment, and prevention: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy. Chest 2004; 126(suppl):311S-337S

The corresponding author had full access to all of the data and had final responsibility for the decision to submit for publication. Manuscript received July 20, 2004; revision accepted November 29, 2004.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal. org/misc/reprints.shtml).

Correspondence to: Theodore E. Warkentin, MD, Hamilton Regional Laboratory Medicine Program, Hamilton Health Sciences, General Site, 237 Barton St East, Hamilton, ON, L8L 2X2 Canada; e-mail:

COPYRIGHT 2005 American College of Chest Physicians
COPYRIGHT 2005 Gale Group

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