Cardiac Enzyme tests. 1

Transcription

1 Cardiac Enzyme tests An enzyme test is a bld test that measures certain enzyme levels t assess hw well the bdy s systems are functining. They can als be used t determine whether there has been any tissue damage. Cardiac enzyme tests are perfrmed t help diagnse a heart attack and t determine the extent f damage t the heart muscle. Less frequently, cardiac enzyme tests can be used t help diagnse a variety f ther cardivascular cnditins, including crnary artery disease, heart failure and alchlic cardimypathy. Similarly, liver enzyme tests are used t diagnse and mnitr the extent f liver diseases r disrders. There are three factrs that culd interfere with the enzyme test results: vigrus exercise, certain medicatins and (in sme cases) eating befre the test. Patients are strngly encuraged t fllw their physician s rders in rder t maximize the accuracy f their test results. Althugh they can detect damage fr any reasn, cardiac enzyme tests are mst cmmnly used t diagnse and mnitr heart attacks. The enzyme test is a bld test that measures certain enzyme levels within the bld. By measuring enzymes that are specific t the heart, physicians are able t detect a heart attack, assess the damage and determine if there is an nging risk. As enzyme tests becme mre sensitive and widespread, they have becme ne f the mst imprtant tls in diagnsing a heart attack, alng with the presence f ther symptms, such as chest pain and abnrmal readings n an electrcardigram. If a very recent heart attack is suspected, a cardiac enzyme test might be cnducted alng with a myglbin test. Studies have shwn that it takes several hurs (usually three t six) fr cardiac enzyme levels t be elevated after a heart attack. In sme peple, levels are nt elevated fr 12 hurs. The prtein myglbin, hwever, is rapidly 1

2 released during a heart attack, making it pssible t mre quickly and accurately diagnse the cnditin. In general, patients having an acute heart attack will have a diagnsis based n an immediate EKG, resulting in immediate treatment. Bld tests fr cardiac enzymes will be perfrmed, but it may take 6 t 12 hurs fr the test t be abnrmal. These bld tests help diagnsis small heart attacks nt detectable n the EKG r assess the magnitude f large heart attacks. In recent years, the science f cardiac enzyme testing has advanced and has develped mre sensitive tests and better understands hw cardiac enzymes react t stress r muscle damage. Hwever, because f variatins between labratries, there is still sme need fr standardizatin amng test results and cut-ff pints. A cardiac enzyme test measures the bld levels f specific cardiac enzymes. Cardiac enzymes help natural chemical reactins that allw the heart t functin nrmally. These tests have becme extremely imprtant t diagnsis f a heart attack because f predictable swings in enzyme levels after damage t the heart muscle. By measuring the levels f enzymes, physicians are able t tell when a heart attack ccurred, hw severe it was and if damage is nging. The tw mst cmmn cardiac enzyme tests perfrmed are: Creatine kinase (CK) Cardiac trpnin In the past, anther enzyme, lactate dehydrgenase (LDH r LD), was als cmmnly measured. Hwever, recent studies have shwn that the cmbinatin f trpnin and specific CK levels is mre specific t the heart. Accrdingly, lactate dehydrgenase testing is n lnger cnsidered a diagnstic tl fr heart attacks. Alternatively, anther enzyme, aspartate amintransferase (AST), is smetimes measured t detect heart damage. Hwever, AST is a liver enzyme and is mre cmmnly measured as part f a standard liver 2

3 functin test t diagnse and mnitr liver disease. This test is rarely perfrmed in cnnectin with heart attack. Enzyme testing may be dne either as part f an initial diagnstic examinatin r t mnitr the prgress f treatment fr an existing disrder. Sme cnditins require a series f regular enzyme tests ver time. Creatine kinase (CK) Als knwn as creatine phsphkinase (CPK), creatine kinase (CK) is a cardiac enzyme that helps cnvert creatine t creatinine, a reactin that is necessary fr metablism and energy prductin. Creatine kinase is made up f three imprtant isenzymes. CK-BB (CK1). Exists primarily in the brain. CK-BB can be an imprtant indicatr f tissue damage in the brain frm strke, trauma r ther causes. CK-MB (CK2). The primary indicatr used t diagnse a heart attack because it exists in the highest amunt in the heart. If CK-MB makes up mre than 5 percent f a ttal CK level, a heart attack is suspected. CK-MB rarely rises fllwing chest pain caused by angina, pulmnary emblism r heart failure, making it a valuable tl fr determining whether a heart attack is the cause f chest pain. CK-MB levels typically increase t abve nrmal levels abut six hurs after a persn has had a heart attack. Furthermre, if ne part f CK-MB (CK-MB2) is greater than anther part (CK-MB1) by a rati f 1.5 r mre, then this is anther indicatin that a heart attack has ccurred. CK-MB levels can als be used after balln angiplasty and ther catheter-based techniques. Studies have shwn an increased risk f sudden cardiac death with higher CK-MB levels after these prcedures. CK-MB can als be fund in small intestine, uterus, prstate, diaphragm, and tngue. 3

4 CK-MM (CK3). Exists primarily in skeletal muscle. Creatine kinase tests may measure ttal CK levels r may break ut the individual levels f CK-BB, CK-MB and CK-MM. Nrmal results are as fllws: Ttal creatine kinase level (CK ttal). Nrmal levels are 25 t 130 micrgrams per liter fr men and 10 t 150 micrgrams per liter fr wmen. CK levels may be much higher in very muscular peple, and infants up t 1 year may have levels up t fur times the nrmal adult level. Accrding t the American Cllege f Cardilgy (ACC), ttal CK levels shuld nt be used in the diagnsis f heart attack. Instead, the Cllege recmmends that physicians rely n the mre sensitive CK-MB levels, which are specific t the heart. CK-BB. Unless tissue damage in the brain has ccurred, CK- BB levels will be undetectable. CK-MB. Nrmal range is frm undetectable t 7 micrgrams per liter. CK-MM. Nrmal range is frm 5 t 70 micrgrams per liter. Cardiac trpnin There are tw types f cardiac trpnin in cardiac muscle Trpnin T (ctnt) and Trpnin I (ctni). These prteins cntrl the interactins f tw ther substances (actin and mysin) that cause the heart muscle t cntract r squeeze. Nrmal levels f cardiac trpnin in the bld are very lw, but they rise sharply and quickly in respnse t a heart muscle injury, usually within tw r three hurs after the beginning f a heart attack. Unlike creatine kinase (CK), cardiac trpnin will als rise in respnse t angina, which is ne reasn the tw tests are ften perfrmed tgether. Cardiac trpnin is mre sensitive t damage than CK and is therefre valuable at detecting mild heart attacks and early detectin f ther heart prblems. Trpnin T and I levels have als been used t help predict a patient s heart attack risk because f their sensitivity 4

5 and the fact that elevated levels are specific t a heart injury. Because trpnin is filtered by the kidneys, it had been held that trpnin level testing was nt reliable in patients with renal disease. Recent studies have shwn, hwever, that the test is sensitive enugh even when the kidneys are nt functining nrmally. It is believed that the results f a trpnin test culd help identify peple at a higher risk f a serius cardivascular prblem r death. Nrmal cardiac trpnin levels are listed belw. Hwever, it is imprtant t nte that because f variatins between individual labratries, these numbers might vary fr individual patients: ctnt. Nrmal range is less than 0.1 nangrams per milliliter. ctni. Nrmal range is less than 0.4 nangrams per milliliter. Lactate dehydrgenase Until recently, levels f lactate dehydrgenase (LDH) were used t measure cardiac damage. Hwever, there were certain drawbacks with this apprach. LDH is an enzyme that helps cnvert lactic acid t pyruvic acid. It is present in nearly all bdy tissues. Because trpnin is specific t cardiac muscle, the LDH test has largely been replaced by the trpnin test. Currently, the American Cllege f Cardilgy (ACC) des nt recmmend measuring LDH in the diagnsis f heart attack. Aspartate amintransferase Frmerly knwn as serum glutamic-xalacetic transaminase (SGOT), aspartate amintransferase (AST) is ne f tw enzymes that cnvert amin acids t amin acid residues, which is vital t energy prductin. Nrmal AST levels are 8 t 20 micrgrams per liter, but infants up t 1 year may have levels up t fur times the nrmal adult level. 5

6 Increases in AST levels are prprtinal t cell damage within the bdy, making it an imprtant tl fr mnitring the prgressin f damage and the healing prcess. The degree t which AST is elevated can als help pinpint the type f cell damage that has ccurred. Fr example: A maximum increase f 20 times nrmal usually indicates severe viral hepatitis, severe trauma r surgery. A high level f 10 t 20 times nrmal may indicate a heart attack r alchlic cirrhsis f the liver. Mderate t high levels f five t 10 times nrmal culd be caused by muscular dystrphy r chrnic hepatitis. Lw levels f tw t five times nrmal may indicate a number f cnditins, including pulmnary emblism, and disrders f the liver r pancreas. Thugh AST is smetimes used t track heart attack patients, it is nt used as cmmnly fr this purpse as CK r LDH. AST is mre cmmnly used t track liver disease as a cmpnent f liver enzyme testing. Heart damage and cardiac enzymes When heart damage ccurs the heart releases enzymes at a predictable pace. Trpnin levels begin t rise tw t fur hurs after a heart attack and peak within 10 t 24 hurs. Elevated levels can still be detected a week r mre after the nset f chest pain. CK-MB levels begin t rise fur t six hurs after a heart attack and may remain elevated fr up t 48 hurs after the heart attack. The degree the CK-MB level rises depends n the severity f the heart attack. When these enzyme levels begin t decline, it is a sign that the heart attack stpped several hurs earlier. Heart muscle cannt heal itself, hence the imprtance f rapid diagnsis and treatment. 6

7 Based n this infrmatin, physicians can determine frm cardiac enzyme tests that: Cardiac enzymes will demnstrate increased levels fllwing heart damage. If subsequent tests shw that enzyme activity is decreasing, the heart attack stpped several hurs ag and the heart tissue may be healing. If enzyme activity cntinues t increase, it is likely that the heart attack was larger than initially thught. If enzyme activity plateaus, begins t decline, then rises again, it is likely a secnd, fllw-up heart attack is ccurring. The extent f the heart attack based n the magnitude f rise f the enzymes. Enzyme testing may be dne as part f making an initial diagnsis r t mnitr the prgress f treatment fr a disrder. Sme cnditins will require a series f regular enzyme tests ver time. Understanding cardiac enzyme test results Higher-than-nrmal enzyme levels indicate tissue damage in ne r mre areas f the bdy. Cnditins that may have caused the damage include but are nt limited t the fllwing: Heart attack. An event that results in permanent heart damage r death. It is als knwn as a mycardial infarctin, because part f the heart muscle (mycardium) may literally die (infarctin). It is caused by a lengthy r severe episde in which the heart is nt getting enugh xygen-rich bld. Over time, the accumulated effects f tissue damage frm a heart attack can lead t heart failure. 7

8 Cardiac ischemia. A temprary episde in which part f the heart is nt getting enugh xygen rich bld. Whether r nt cardiac enzyme testing is valuable as a screening and diagnsis tl fr nn-acute heart disease is actually a cntrversial issue amng physicians. Sme physicians believe that particularly trpnin testing can help diagnse ischemic heart disease, while cntrlled studies f subjects in stress testing has nt cnsistently shwn elevatins in enzymes due t ischemia. In additin, trpnins may be elevated in respnse t a wide variety f diseases. Hwever, because trpnins are generally nly elevated in respnse t a disease smewhere in the bdy, any elevatin f trpnins shuld be taking seriusly. Strke. An event in which the brain des nt receive enugh xygen-rich bld, as a result f either an bstructing bld clt in a majr artery (e.g., ne f the cartid arteries) r excessive bleeding int the brain (cerebral hemrrhage). Pericarditis. An inflammatin f the pericardium a thin, fluidfilled sac surrunding the heart. Alchlic cardimypathy. An enlargement, stiffening r thickening f the heart muscle due t excessive cnsumptin f alchl. As a result, the heart muscle s ability t pump bld is ften weakened. Lw bld pressure (hyptensin). Heart failure. A serius cnditin in which the heart is nt pumping well enugh t meet the bdy s demand fr xygen. It gets its name because the heart is failing t pump efficiently, which ften results in cngestin in the lungs. Crnary artery disease. A chrnic disease in which there is a hardening (athersclersis) f the arteries n the surface f the heart. The term hardening refers t a cnditin that causes the arteries t becme s narrwed and stiff that they blck the free flw f bld. Many patients have symptms 8

9 such as chest pain, pressure r discmfrt angina, but ther patients have n warning signs befre a ttal blckage ccurs, which can lead t heart attacks. Platelet disrders. Platelets are cmpnents in bld necessary t the frmatin f bld clts. Muscular dystrphy. A prgressive, ften inherited disease characterized by the deteriratin f muscle. Hypthyridism. An underactive thyrid gland that leads t a deficiency f thyrid hrmne in the bdy. Hypkalemia. A deficiency f ptassium in the bld. Carbn mnxide pisning. Seizures r cnvulsins. Pulmnary infarctin (lung tissue death). Leukemia, lymphma r brain cancer. Hemlytic anemia. A type f anemia (red bld cell deficiency) caused by the premature destructin f red bld cells. Liver, kidney r pancreas disrders. Trauma frm accident, injury r electric shck. Lwer-than-nrmal enzyme levels may indicate: Malnutritin. Inadequate nutritin that may be caused by either an unbalanced diet r malabsrptin a cnditin in which the bdy has difficulty digesting r absrbing nutrients frm fd. Cngenital enzyme disrder. Metablic disrders present frm birth that prduce a deficiency in ne r mre enzymes. 9

10 Liver enzyme tests Liver enzymes are enzymes that help perfrm chemical reactins in the bdy necessary t nrmal liver functins. The liver enzyme tests mst cmmnly perfrmed are: Aspartate amintransferase (AST). Althugh AST is nt specific t liver disease, levels are a vital cmpnent f liver enzyme testing because it is the best enzyme t use in tracking bth the tissue damage and the healing prcess. As nted earlier, nrmal levels are 8 t 20 micrgrams per liter, but infants up t 1 year may have levels up t fur times the adult nrmal. A maximum increase f 20 times nrmal usually indicates severe viral hepatitis, severe trauma r surgery. A high level f 10 t 20 times nrmal may indicate a heart attack r alchlic cirrhsis. Mderate t high levels f five t 10 times nrmal culd be caused by muscular dystrphy r chrnic hepatitis. Lw levels f tw t five times nrmal may indicate a number f cnditins, including pulmnary emblism, and disrders f the liver r pancreas. Alanine amintransferase (ALT), frmerly knwn as serum glutamate pyruvate transaminase (SGPT). ALT is ne f tw enzymes that cnvert amin acids t amin acid residues, which is vital t energy prductin. Nrmal levels are 8 t 20 micrgrams per liter. Lw levels ccur during a heart attack. Mderate levels indicate cirrhsis. 10

11 Mderate t high levels indicate chrnic hepatitis fr severe liver cngestin due t heart failure. Very high ALT levels, up t 50 times greater than nrmal, are an indicatin f severe hepatitis (inflammatin f the liver) caused by infectin r medicatins. Alkaline phsphatase (ALP). An enzyme fund primarily in the liver, bnes, kidneys and intestinal lining that influences bne grwth and the transprt f fats (lipids) thrugh the bldstream. ALP increases may be caused by bld disrders r liver disease and, in cmbinatin with ther enzyme tests, ALP levels can be used t differentiate between the tw. Nrmal levels are 90 t 239 micrgrams per liter fr males, 76 t 196 micrgrams per liter fr females under age 45 and 87 t 250 micrgrams per liter fr females ver age 45. Children have higher levels than adults because their bnes are still grwing. Mderate increases in ALP are usually caused by bile bstructins r liver infectins, but can als be an indicatr f rickets frm vitamin D deficiency. Higher levels may indicate liver diseases causing bstructins r skeletal diseases that cause rapid bne grwth. Gamma glutamyl transferase (GGT), als called gamma glutamyl transpeptidase. An enzyme fund primarily in the kidneys that is invlved in the transfer f amin acids acrss cell membranes. Recent studies suggest that elevated levels f GGT may indicate an increased risk f death frm cardivascular disease. Nrmal GGT levels are 8 t 37 micrgrams per liter in males and 5 t 24 micrgrams per liter in females under age 45 and 6 t 37 micrgrams per liter fr females ver 11

12 age 45. In cmbinatin with an elevated ALP, a nrmal GGT level indicates that the ALP elevatin is being caused by a bne disrder, nt liver dysfunctin. An elevated GGT level five t 10 days fllwing a heart attack is either a sign f the healing prcess r that the weakened heart is affecting liver functins. A variety f factrs can influence liver enzyme levels including drugs, tumrs, infectins, txins r trauma. When liver damage ccurs, the enzymes are released in stages, similar t the cardiac enzymes. When all f these enzyme levels begin t decline, it is a sign that the damaged liver is beginning t heal. Measuring a single enzyme level will nt diagnse a cnditin, but a cmbinatin can prvide valuable infrmatin t help in the diagnsis and management f varius cnditins. Enzyme testing may be dne either as part f making an initial diagnsis r t mnitr the prgress f treatment fr an existing disrder. Sme cnditins will require a series f regular enzyme tests ver time. 12