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Cardiovascular Lab Tests

Cardiovascular Lab Tests. Dr. Felix Hernandez M.D. Complete Blood Count (CBC). A series of tests of the peripheral blood that provides valuable information about the hematologic system. Is very inexpensive and can be performed rapidly. CBC. Includes measurement of the following: RBC count

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Cardiovascular Lab Tests

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  1. Cardiovascular Lab Tests • Dr. Felix Hernandez M.D.

  2. Complete Blood Count (CBC) • A series of tests of the peripheral blood that provides valuable information about the hematologic system. • Is very inexpensive and can be performed rapidly

  3. CBC • Includes measurement of the following: • RBC count • Hemoglobin • Hematocrit • Mean Corpuscular Volume • Mean Corpuscular Hemoglobin • White Blood Cell Count w/ Differential • Neutrophils • Lymphocytes • Monocytes • Eosinophils • Basophils • Platelet Count

  4. RBC Count • Test Range and Collection • (RBC, or erythrocyte count), whole blood • 4.3–6.0 x 106/mcL (male) • 3.5–5.5 x 106/mcL (female) • Physiologic Basis • Red blood cells (erythrocytes) are counted by automated instruments using electrical impedance or light scattering. • Interpretation • Increased in: Secondary polycythemia, hemoconcentration (dehydration), Polycythemia Vera. Spurious increase with increased white blood cells. • Decreased in: Anemia. Spurious decrease with autoagglutination (eg, cold agglutinins).

  5. Hemoglobin • Test Range and Collection • whole blood (Hb) • Male: 13.6–17.5 • Female: 12.0–15.5 g/dL (age-dependent) • Physiologic Basis • Hemoglobin is the major protein of erythrocytes that transports oxygen from the lungs to peripheral tissues. • It is measured by spectrophotometry on automated instruments after hemolysis of red cells and conversion of all hemoglobin to cyanmethemoglobin. • Interpretation • Increased in:Hemoconcentration (as in dehydration, burns, vomiting), polycythemia, extreme physical exercise. • Decreased in: Macrocytic anemia (liver disease, hypothyroidism, vitamin B12 deficiency, folate deficiency), normocytic anemia (early iron deficiency, anemia of chronic disease, hemolytic anemia, acute hemorrhage), and microcytic anemia (iron deficiency, thalassemia). • Hypertriglyceridemia and very high white blood cell counts can cause false elevations of Hb

  6. Hematocrit • Test Range and Collection • whole blood (Hct) • Male: 39–49% • Female: 35–45% • (age-dependent) • Physiologic Basis • The Hct represents the percentage of whole blood volume composed of erythrocytes. • Laboratory instruments calculate the Hct from the erythrocyte count (RBC) and the mean corpuscular volume (MCV) by the formula: • Hct = RBC x MCV • Interpretation • Increased in: Hemoconcentration (as in dehydration, burns, vomiting), polycythemia, extreme physical exercise. • Decreased in: Macrocytic anemia (liver disease, hypothyroidism, vitamin B12 deficiency, folate deficiency), normocytic anemia (early iron deficiency, anemia of chronic disease, hemolytic anemia, acute hemorrhage), and microcytic anemia (iron deficiency, thalassemia). • Conversion from hemoglobin (Hb) to hematocrit is roughly Hb x 3 = Hct. • In hemodialysis patients, maintaining an Hct in the range of 33–36% provides best outcomes in studies of hospitalizations and mortality.

  7. Mean Corpuscular Volume (MCV) • Test Range and Collection • blood (MCV) • 80–100 fL • Physiologic Basis • MCV is the average volume of the red cells, and it is measured by automated instrument (electrical impedance or light scatter). • Interpretation • Increased in: Liver disease (alcoholic and nonalcoholic), alcohol abuse, HIV/AIDS, hemochromatosis, megaloblastic anemia (folate, vitamin B12 deficiencies), reticulocytosis, newborns. Spurious increase in autoagglutination, high white blood cell count. Drugs: methotrexate, phenytoin, zidovudine. • Decreased in: Iron deficiency, thalassemia, sideroblastic anemia, hereditary spherocytosis, and some anemia of chronic disease. • MCV can be normal in combined iron and folate deficiency. • In patients with two red cell populations (macrocytic and microcytic), MCV may be normal.

  8. Mean Corpuscular Hemoglobin • Test Range and Collection • blood (MCH) • 26–34 pg • Physiologic Basis • MCH indicates the amount of hemoglobin per RBC in absolute units. • MCH is calculated from measured values of hemoglobin (Hb) (g/dL) and RBC/L by the formula: • MCH = (Hb/RBC) x 10 • Interpretation • Increased in: Macrocytosis, hemochromatosis. • Decreased in: Microcytosis (iron deficiency, thalassemia), hypochromia (lead poisoning, sideroblastic anemia, anemia of chronic disease). • Low MCH can mean hypochromia or microcytosis or both. • High MCH is evidence of macrocytosis.

  9. White Blood Cell Count w/ Differential • Test Range and Collection • blood • Reference ranges are age- and laboratory-specific • Adult ranges: WBC 4.5–11.0 x 103/mcL; • differential: • segmented neutrophils 50–70%; • band neutrophils 0–5%; • lymphocytes 20–40%; • monocytes 2–6%; • eosinophils 1–4%; • basophils 0–1%. • Panic: <1.5 x 103/mcL

  10. White Blood Cell Count w/ Differential • Physiologic Basis • The WBC count and differential determine the number of white blood cells and the percentage of each type of white cell in a blood sample. It is typically generated by an automated laboratory hematology analyzer as part of the CBC panel. • Manual differential is also routinely obtained by examing a blood smear under a microscope. • Interpretation • Increased in: Acute infections, inflammatory disorders, acute and chronic leukemias, myeloproliferative disorders, circulating lymphoma, tissue injury/necrosis, various drugs, corticosteroids, allergies, hypersensitivity reactions, stress, smoking. • Decreased in: Infections, constitutional and acquired myeloid hypoplasia, myelosuppression (eg, chemotherapy, radiation, various drugs), myelodysplasia, collagen vascular diseases, hypersplenism, cyclic neutropenia, autoimmune neutropenia, alcoholism • It is important to perform a manual differential in certain conditions such as presence of blasts, immature granulocytes, nucleated red blood cells, leukemia or lymphoma cells, plasma cells, or dysplasia.

  11. Platelet Count • Test Range and Collection • whole blood (Plt) • 150–450 x 103/mcL • [x 109/L] • Panic: <25 x 103/mcL • Physiologic Basis • Platelets are released from megakaryocytes in bone marrow and are important for normal hemostasis. • Platelet counting is performed as part of the complete blood cell count (CBC) panel. It is typically obtained by automated hematology analyzer. • Interpretation • Increased in:Myeloproliferative disorders (chronic myeloid leukemia, essential thrombo-cythemia, myelofibrosis), acute blood loss, post-splenectomy, pre-eclampsia, reactive thrombocytosis secondary to inflammatory disorders, infection, tissue injury, iron deficiency, malignancies. • Decreased in: Decreased production: bone marrow suppression or replacement/infiltration, chemotherapy, drugs, alcohol, infection (eg, HIV), congenital marrow failure (eg, Fanconi anemia, Wiskott-Aldrich syndrome, Thrombocytopenia with Absent Radius (TAR) syndrome, etc); increased destruction or excessive pooling: hypersplenism, DIC, platelet antibodies (idiopathic thrombocytopenic purpura, Evans' syndrome, posttransfusionpurpura, neonatal isoimmune thrombocytopenia, drugs [eg, quinidine, cephalosporins, clopidogrel, HIT])

  12. Platelet Count • Platelet counts are determined in patients with suspected bleeding disorders, purpura or petechiae, leukemia/lymphoma, DIC, in patients on chemotherapy, and to determine the response to platelet transfusions. • There is little tendency to bleed until the platelet couint falls below 20,000/mcL. Bleeding due to low platelet counts typically presents as petechiae, epistaxis, and gingival bleeding. For invasive procedures, platelet counts above 50,000/mcL are desirable. • HIV infection may result in both decreased platelet production and decreased platelet survival.

  13. Coagulation Screening • Used to evaluate a patient’s blood coagulation system status • Has multiple factors that are measured: • Prothrombin Time (PT) • Partial Thromboplastin Time (PTT) • INR

  14. Prothrombin Time • Test Range and Collection • whole blood (PT) • 11–15 seconds • (laboratory specific) • Physiologic Basis • PT evaluates the extrinsic and common coagulation pathways. It is performed by adding calcium and tissue thromboplastin to a sample of citrated, platelet-poor plasma, and measuring the time required for fibrin clot formation. • It is most sensitive to deficiencies in the vitamin K-dependent clotting factors II, VII, and X. It is also sensitive to deficiency of factor V. It is less sensitive to fibrinogen deficiency and heparin. • PT is the most commonly used test for monitoring warfarin therapy. • Interpretation • Increased in: Warfarin, liver disease, DIC, vitamin K deficiency, hereditary deficiency in factors VII, X, V and II, fibrinogen abnormality (eg, hypofibrinogenemia, afibrinogenemia, dysfibrinogenemia), circulating anticoagulant affecting the PT system (rarely lupus anticoagulant), massive transfusion. • Routine preoperative measurement of PT is unnecessary unless there is clinical history of a bleeding disorder

  15. Partial Thromboplastin Time (PTT) • Test Range and Collection • activated, plasma • (aPTT) • 25–35 seconds (range varies) • Panic: 60 seconds (off heparin) • Physiologic Basis • The aPTT is a clot-based test in which phospholipid reagent, an activator substance, and calcium are added to the patient's plasma, and the time for a fibrin clot to form is measured. • PTT evaluates the intrinsic and common coagulation pathways and adequacy of all coagulation factors except XIII and VII. • PTT is usually abnormal if any factor level drops below 25–40% of normal, depending on the PTT reagent used. • PTT is commonly used to monitor heparin therapy. • Interpretation • Increased in: Deficiency of any individual coagulation factor except Factors XIII and VII, presence of nonspecific inhibitor (eg, lupus anticoagulant), specific factor inhibitor, von Willebrand disease (PTT may also be normal), hemophilia A and B, DIC. Drugs: heparin, direct thrombin inhibitor (eg, hirudin, argatroban), warfarin. • Decreased in:Hypercoagulable states (eg, increased factor VIII levels). • PTT cannot be used to monitor very high doses of heparin (eg, cardiac bypass surgery) because the clotting time is beyond the analytical measurement range of PTT.

  16. INR • Test Range and Collection • International Normalized Ratio (INR) is calculated. • INR = [Patient PT/Normal mean PT] • Physiologic Basis • The INR was introduced in the early 1980s to improve PT reporting and standardization. An International Sensitivity Index (ISI) is assigned to each thromboplastin by the reagent manufacture. The ISI is a measure of a reagent's respnsiveness to low levels of vitamin K-dependent factors compared with the WHO International Reference Preparation. • Interpretation • Warfarin therapeutic range is INR 2.0–3.0. Bleeding has been reported to be three times more common in patients with INRs of 3.0–4.5 than in patients with INRs of 2.0–3.0.

  17. Cardiac Injury Lab Tests • Are part of the diagnostic procedure for myocardial infarctions. • Measure various substances that are released by myocytes upon injury • Individual Substances Include: • Creatine Kinase • CK-MB • Troponin I

  18. Creatine Kinase • Test Range and Collection • serum (CK) • 32–267 IU/L • [0.53–4.45 mckat/L] (method-dependent) • Physiologic Basis • Creatine kinase splits creatine phosphate in the presence of ADP to yield creatine and ATP. • Skeletal muscle, myocardium, and brain are rich in the enzyme. • CK is released by tissue damage. • Interpretation • Increased in: Myocardial infarction (MI), myocarditis, muscle trauma, rhabdomyolysis, muscular dystrophy, polymyositis, severe muscular exertion, malignant hyperthermia, hypothyroidism, cerebral infarction, surgery, Reye syndrome, tetanus, generalized convulsions, alcoholism, IM injections, DC countershock. Drugs: clofibrate, HMG-CoA reductase inhibitors. • During an MI, serum CK level rises rapidly (within 3–5 hours); elevation persists for 2–3 days post-MI. • Total CK is not specific enough for use in diagnosis of MI, but a normal total CK has a high negative predictive value. A more specific test is needed for diagnosis of MI or acute coronary syndrome (eg, CK-MB, now largely replaced by cardiac troponin I).

  19. Creatine Kinase MB • Test Range and Collection • serum enzyme activity (CK-MB) • <16 IU/L • Physiologic Basis • CK consists of three isoenzymes, made up of 2 subunits, M and B. The fraction with the greatest electrophoretic mobility is CK1 (BB), CK2 (MB) is intermediate, and CK3 (MM) moves slowest toward the anode. • Skeletal muscle is characterized by isoenzyme MM and brain by isoenzyme BB. • Myocardium has approximately 40% MB isoenzyme. • Interpretation • Increased in: Myocardial infarction, cardiac trauma, certain muscular dystrophies, and polymyositis. Slight persistent elevation reported in a few patients on hemodialysis. • CK-MB is a relatively specific test for MI. It appears in serum approximately 4 hours after infarction, peaks at 12–24 hours, and declines over 48–72 hours. CK-MB mass concentration is a more sensitive marker of MI than CK-MB isoenzymes or total CK within 4–12 hours after infarction. Cardiac troponin I levels are useful in the late (after 48 hours) diagnosis of MI because, unlike CK-MB levels, they remain elevated for 5–7 days. Within 48 hours, sensitivity and specificity of troponin I are similar to CK-MB. Specificity of troponin I is higher than CK-MB in patients with skeletal muscle injury or renal failure, or postoperatively. Cardiac troponin I is therefore the preferred test. • Estimation of CK-MM and CK-BB is not clinically useful. Use total CK.

  20. Troponin I • Test Range and Collection • serum ( Cardiac Troponin I: cTnI) • <1.5 ng/mL (method- dependent) • Physiologic Basis • Troponin is the contractile regulatory protein of striated muscle. It contains three subunits: T, C, and I. • Subunit I consists of three forms, which are found in slow-twitch skeletal muscle, fast-twitch skeletal muscle, and cardiac muscle, respectively. • Troponin I is predominantly a structural protein and is released into the circulation after cellular necrosis. Cardiac troponin I is expressed only in cardiac muscle, throughout development and despite pathology, and thus its presence in serum can distinguish between myocardial injury and skeletal muscle injury.

  21. Troponin I • Interpretation • Increased in: Myocardial infarction (sensitivity 50% at 4 hours, 97% at 6 hours; specificity 95%), cardiac trauma, cardiac surgery, myocardial damage following PTCA, and other cardiac interventions, nonischemic dilated cardiomyopathy, prolonged supraventricular tachycardia, acute dissection of the ascending aorta. Slight elevations noted in patients with recent aggravated unstable angina, muscular disorders, CNS disorders, HIV infection, chronic renal failure, cirrhosis, sepsis, lung diseases, and endocrine disorders. • Not increased in: Skeletal muscle disease (myopathy, myositis, dystrophy), external electrical cardioversion, noncardiac trauma or surgery, rhabdomyolysis, severe muscular exertion, chronic renal failure.

  22. Troponin I • Interpretation • Cardiac troponin I is a more specific marker for myocardial infarction than CK-MB with roughly equivalent sensitivity early in the course of infarction (4–36 hours). • Sensitivity and specificity for peak concentrations of cTnI (100%; 96%) are equivalent to or better than those for CK-MB (88%; 93%) and total CK (73%; 85%). • cTnI appears in serum approximately 4 hours after onset of chest pain, peaks at 8–12 hours, and persists for 5–7 days. This prolonged persistence gives it much greater sensitivity than CK-MB for diagnosis of myocardial infarction beyond the first 36–48 hours.

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