Pseudothrombocytopenia in a patient undergoing splenectomy of an accessory spleen: case report

Abstracts

JUSTIFICATIVA E OBJETIVOS: Os testes de coagulação (hemograma e tempo de protrombina) foram inicialmente concebidos como uma forma de rastrear e acompanhar coagulopatias congênitas raras e o hemograma é o que fornece o número de plaquetas por milímetro cúbico. O objetivo deste relato foi apresentar o caso de uma paciente que apresentava um número de plaquetas extremamente baixo quando sua amostra de sangue era analisada em tubo com EDTA e um número normal quando analisada com citrato, alertando para o risco de administração errônea de hemoderivados. RELATO DO CASO: Paciente do sexo feminino, 40 anos, ASA II. Em 2001, apresentou plaquetopenia no hemograma e foi encaminhada para o hematologista em Manaus, AM, sendo realizada esplenectomia nesse mesmo ano, com diagnóstico de púrpura trombocitopênica idiopática. Com a persistência da plaquetopenia nos hemogramas foi verificado na ecografia de abdômen: imagem hipoecóica de ecotextura semelhante à esplênica, medindo 2,0 × 1,7 cm, forma esférica, conteúdo bem definido (baço acessório) e indicada esplenectomia de baço acessório. Após uma hora de operação, foram colhidas amostras para hemograma e bioquímica: Hb = 11,3 g.dL-1; Ht = 33,4%; Plaquetas = 35.000.µL-1; TAP = 15,2 (86,0% Atividade) (RNI = 1,09). Em virtude do sangramento mínimo no campo cirúrgico, foi solicitado novo exame com citrato para dosagem de plaquetas (resultado: 138.000 plaquetas). CONCLUSÕES: O resultado anômalo em um exame isolado sem correspondência com a clínica do paciente não deve guiar a terapêutica. Todos os exames têm uma porcentagem definida de erros, e a busca desses erros técnicos impede que uma terapêutica errônea seja usada.

EXAMES COMPLEMENTARES; EXAMES COMPLEMENTARES; SANGUE

CLINICAL REPORT

Pseudothrombocytopenia in a patient undergoing splenectomy of an accessory spleen. Case report^*

Pseudoplaquetopenia en paciente sometida a la esplenectomía de bazo accesorio. Relato de caso

Eduardo Jorge Yamada^I; Anne Francy Pereira Souto^I; Ellen da Encarnação Onety de Souza^I; Cid Amorim Nunes^I; Cremilda Pinheiro Dias, TSA^II

^IAnestesiologista Colaborador do CET/SBA HUGV-UFAM

^IIAnestesiologista; Membro do Comitê em Via Aérea Difícil da SBA

Correspondence to

SUMMARY

BACKGROUND AND OBJECTIVES: Coagulation tests (CBC and prothrombin time) were initially conceived as a mean of screening and following rare congenital coagulopathies; the CBC provides the number of platelets per cubic milliliter. The objective of this report was to present the case of a patient who presented with an extremely low number of platelets when her blood was analyzed in an EDTA-containing tube and its numbers were normal when the blood was analyzed with citrate, alerting for the risk of erroneously administering blood products.

CASE REPORT: This is the case of a 40-year old female patient, ASA II. In 2001 she presented with thrombocytopenia and was referred to a hematologist in Manaus, in the state of Amazonas, Brazil and underwent splenectomy that same year with a diagnosis of idiopathic thrombocytopenic purpura. Since her CBCs continued to show thrombocytopenia, an abdominal ultrasound was done and showed a spherical hypoechoic image, with an echotexture similar to the spleen, measuring 2.0 × 1.7 cm, with well-defined contents (accessory spleen), and a splenectomy was indicated. One hour into the surgery, blood samples were drawn for CBC and chemistry: Hb = 11.3 g.dL^-1; Ht = 33.4%; Platelets = 35,000.µL^-1; PT = 15.2 (86.0% Activity) (INR = 1.09). Due to the minimal blood loss in the surgical field, a new test with citrate was requested to determine the platelet count (results: 138,000 platelets).

CONCLUSIONS: The anomalous result of an isolated exam without corresponding clinical signs should not guide the treatment. All exams have a defined percentage of errors and the search for those technical errors can avoid the use of the wrong treatment.

Key Words: BLOOD: transfusion; COMPLEMENTARY EXAMS: platelet count, pseudothrombocytopenia.

RESUMEN

JUSTIFICATIVA Y OBJETIVOS: Las pruebas de coagulación (hemograma y tiempo de protrombina) fueron inicialmente concebidas como una forma de rastrear y acompañar las coagulopatías congénitas raras, siendo el hemograma el que suministra el número de plaquetas por milímetro cúbico. El objetivo de este relato fue presentar el caso de una paciente que presentaba un número de plaquetas extremadamente bajo cuando su muestra de sangre era analizada en un tubo con EDTA y un número normal cuando se analizaba con citrato, avisando sobre el riesgo de la administración equivocada de hemoderivados.

RELATO DEL CASO: Paciente del sexo femenino, 40 años, ASA II. En 2001, presentó plaquetopenia en el hemograma y fue llevada al hematólogo en Manaus, estado brasileño de Amazonas, siendo realizada la esplenectomía en ese mismo año, con diagnóstico de púrpura trombocitopénica idiopática. Al continuar la plaquetopenía en los hemogramas se verificó en la ecografía de abdomen: imagen hipoecoica de ecotextura similar a la esplénica, midiendo 2,0 × 1,7 cm, forma esférica, contenido bien definido (bazo accesorio) e indicada esplenectomía de bazo accesorio. Después de una hora de operación, se recogieron muestras para hemograma y bioquímica: Hb = 11,3 g.dL^-1; Ht = 33,4%; Plaquetas = 35.000.µL^-1; TAP = 15,2 (86,0% Actividad) (RNI = 1,09). Debido al sangramiento mínimo en el campo quirúrgico, fue solicitado un nuevo examen con citrato para la dosificación de plaquetas (resultado: 138.000 plaquetas).

CONCLUSIONES: El resultado anómalo en un examen aislado en correspondencia con la clínica del paciente, no debe ser el leitmotiv de la terapéutica. Todos los exámenes poseen un porcentaje definido de errores, y la búsqueda de esos errores técnicos impide que una terapéutica equivocada sea usada.

INTRODUCTION

Coagulation tests were conceived as a mean of screening and following rare congenital coagulopathies. Among them, the complete blood count (CBC) provides the number of platelets per cubic milliliter. To prevent coagulation inside the collection tubes, the manufactures use two types of anticoagulants: EDTA (ethylenedinitrilotetraacetic acid) or citrate. Usually, the test tube used for CBC (purple) contains EDTA and the tube used to evaluate the prothrombin time (PT) (blue) contains citrate. In specific situations, a reaction between EDTA and platelets can develop causing platelet aggregation around the EDTA molecule, inducing an error by the equipment. The objective of this report was to present the case of a patient with an extremely low platelet number when her blood was analyzed in an EDTA-containing tube and normal number of platelets on the citrate-containing tube, and warn physicians in general for the dangers of the improper administration of blood products.

CASE REPORT

A female patient, 40 years old, 68 kg, 1.65 m, physical status ASA II, was referred for resection of an accessory spleen. In 2001, she presented thrombocytopenia during a routine work-up and was referred to a Hematology service. She had one episode of epistaxis, which was controlled by applying pressure. Splenectomy was indicated on that same year; she was given the diagnosis of idiopathic thrombocytopenic purpura and treated with 10 mg of prednisone a day. On the following years, she continued to present thrombocytopenia in her CBCs, but without bleeding, episodes of epistaxis, or purpuric lesions. Preoperative laboratory work up was as follows: Hb 12.3 g.dL^-1; Ht 37.3%; platelets 57,000.µL^-1; PTP15.2 sec (86%); INR 1.09. The electrocardiogram was normal. Ultrasound of the abdomen showed a spherical hypoechoic image with echotexture similar to the spleen, measuring 2.0x1.7 cm, with well-defined contents (accessory spleen). The preoperative evaluation was performed the day before the surgery; general anesthesia was indicated and the probability of platelet transfusion was raised. Pre-anesthetic medication consisted of 10 mg of oral diazepam. Upon arrival to the operating room, monitoring with cardioscopy, pulse oximeter, and non-invasive blood pressure was instituted. Venipuncture was performed with two 18G catheters: one in each upper limb. Denitrogenization was initiated with the administration of 5 L.min^-1 of oxygen via face mask; 300 µg of fentanyl, 200 mg of propofol, and 30 mg of atracurium were used for anesthetic induction; a 7.5 ETT with cuff was used for the tracheal intubation. Maintenance was accomplished with oxygen and 1% isoflurane, 10 mg of atracurium 30 minutes after induction, and 100 mg of hydrocortisone. One hour into the surgery, blood samples were drawn for CBC and chemistry. The results showed Hb 11.3 g.dL^-1; Ht 33.4%; platelets 35,000.µL^-1; PT 15.2 sec (86.0% activity) (INR = 1.09). Due to minimal blood loss in the surgical field, a new CBC with citrate was requested, which showed 138,000 platelets.µL^-1 and microscopic exam of the blood with EDTA showed platelet aggregates around the immunoglobulin (Figure 1). It was requested microscopic exam of citrated blood on a slide (free and dispersed platelets) (Figure 2). Patient had no intercurrences postoperatively, and was discharged from the hospital 48 hours after the surgery. To confirm that the blood tests were not mistaken, the patient was asked to return after seven days for new blood tests. Blood samples were divided in three pairs of EDTA and citrate tubes. Four of the six tubes were provided by other hospitals (a pair of EDTA/citrate from hospital A and another pair from hospital C), while the remaining pair was from the hospital the patient was operated. New measurements of all tubes were analyzed by the laboratory equipment (Table I) and, afterwards, they were evaluated microscopically to compare the results (Figures 3 to 8).

DISCUSSION

Platelets are derived from megakaryocytes, multinucleated cells present in small number in the bone marrow. Megakaryocytes are derived from stem cells under the influence of growth factors (interleukin-3, interleukin-6, macrophage-granulocyte stimulating factor, and interleukin-11) and a specific thrombopoetin ¹.

Thrombocytopenia occurs when platelet count is below 150,000 per milliliter of blood. Daily platelet production is around 15,000 to 45,000 and they have a half-life of 9 to 10 days. Fluctuation is minimal during a 24-hour period. The level of thrombopoetin increases as the number of platelets decreases and vice-versa. In the absence of thrombopoetin, the volume of megakaryocytes can decrease up to 80%. Exogenous erythropoietin can increase the number of megakaryocytes in three days, and the platelet number increases after 5 days. Platelets are the main factors to stimulate the coagulation cascades. Coagulation is not a serum or plasma event, but it is mediated by platelets and controlled by ligands on the surface of the platelet.

Thrombocytopenia is the most common cause of abnormal bleeding and usually is the result of four factors, acting together or isolatedly: (1) thrombocytopenia resulting from artifact (for example, inadequate counting or consumption); (2) deficit in platelet production; (3) increased destruction; and (4) abnormal distribution ¹. When the patient has low platelet numbers in the absence of a consistent clinical history, one should suspect of pseudothrombocytopenia. Although pseudothrombocytopenia is the most common artifact, one should not forget other causes, such as the presence of giant platelets or platelet satelitism ^1,3,4. Pseudothrombocytopenia is usually caused by the anti-coagulant Ethylenediaminetetraacetic acid (EDTA) (a calcium chelator). EDTA alters the conformation of platelet glycoproteins, and anti-coagulant dependent agglutinins (IgG, IgA, or IgM) bind several altered platelets, resulting in platelet aggregation (Figures 3, 5, and 7). There is evidence that the glycoprotein IIb/IIIa is the main protein altered ^3,4. In the presence of multiple platelet aggregates, computerized equipment cannot identify platelets adequately, resulting in an erroneous counting. This can be corrected by visualizing the blood on a microscope (Figures 3 to 8) ^1,3,4.

One should use the citrate-containing tube to determine the number of platelets, and this is the fastest test to detect pseudothrombocytopenia ^1,3.

As for correction of thrombocytopenia with EDTA, Sakurai ⁵ states that the addition of aminoglycosides (kanamycin) to the EDTA-containing tube before drawing the blood prevents the change in platelet count. Maintaining appropriate tubes with kanamycin in the anesthetic context is impractical and it is better to send the sample to be analyzed in a citrate-containing tube when pseudothrombocytopenia is suspected.

Early identification of a patient with thrombocytopenia decreases the risk of transmission if infectious diseases by preventing unnecessary transfusion of platelets.

REFERENCES

• 01. Puyo CA - Thrombocytopenia. Int Anesthesiol Clin, 2001;39: 17-34.
• 02. Spiess BD - Coagulation in the perioperative period. Int Anesthesiol Clin, 2004;42:55-71
• 03. Dalamangas LC, Slaughter TF - Ethylenediaminetetraacetic acid-dependent pseudothrombocytopenia in a cardiacal surgical patient. Anesth Analg, 1998;86:1210-1211.
• 04. Pegels JG, Bruynes ECE, Engelfriet CP et al. - Pseudothrombocytopenia: an immunologic study on platelet antibodies dependent on ethylene diamine tetra-acetate. Blood, 1982; 59:157-161.
• 05. Sakurai S, Shiojima I, Takeshi T et al. A- minoglycosides prevent and dissociate the aggregation of platelets in patients with EDTA-dependent pseudothrombocytopenia. Brit J Haematol, 1997;99:817-823.
• 06. Goodnough LT - Risks of blood transfusion. Crit Care Med, 2003;31:S678-S86.
• 07. Wall MH, Prielipp RC - Transfusion in the operating room and the intensive care unit: current practice and future directions. Int Anesthesiol Clin, 2000;38:149-169.

*

Recebido do Hospital Universitário Getúlio Vargas (HUGV) da Universidade Federal do Amazonas (UFAM), Manaus, AM

Publication Dates

• Publication in this collection
  12 Sept 2008
• Date of issue
  Oct 2008

History

• Accepted
  26 May 2008
• Received
  01 Dec 2007