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Liver MSc Clinical Biochemistry Dr Sarah Mapplebeck Consultant Clinical Biochemist Lecture structure Session 1 Liver structure and function Liver investigations Session 2 Liver cases Session 1 STRUCTURE AND FUNCTION Structure of liver Largest internal organ Situated in right hypochnodrium Divided into right and left lobes by middle hepatic vein Subdivided into eight segments by divisions of the right, middle and left hepatic vein Blood supply Blood supply to liver constitutes 25% of resting cardiac output via two main vessels Hepatic artery Branch of coeliac axis Supplies 25% of total blood flow Autoregulation of blood flow by hepatic artery ensure a constant total liver blood flow Portal vein Drains most of the GI tract and Supplies 75% of blood flow spleen Functions of the liver Metabolic Protein metabolism Carbohydrate metabolism Lipid metabolism Formation of bile Metabolism and excretion of bilirubin Hormone and drug inactivation Protein metabolism Synthesis Principal site of synthesis of most circulating proteins Receives amino acids from intestine and muscle and regulates plasma levels Plasma contains approx 60-80 g/L (albumin, globulin, fibrinogen) Transport proteins e.g transferrin, caeruloplasmin produced in liver Coagulation factors and complement components Degradation (nitrogen excretion) Amino acids degraded by transamination and oxidative deamination to ammonia Ammonia converted to urea and is renally excreted Failure of excretion occurs in severe liver disease Carbohydrate metabolism Glucose homeostasis and maintenance of blood sugar major function of liver Stores approx 80g glycogen Immediate fasting state Blood glucose maintained by glucose released from glycogen breakdown (glycogenolysis) or by newly synthesized glucose (gluconeogensis) Sources for gluconeogensis are lactate, pyruvate, amino acids from muscle (alanine and glutamine) Prolonged starvation Ketone bodies and fatty acids are used as alternative sources of fuel Body adapts to lower glucose requirement Lipid metabolism Fats transported in plasma as lipoproteins (protein-lipid complexes) Liver has major role in metabolism of lipoproteins VLDL and HDL synthesised by liver Triglycerides (come from diet) also synthesised in liver from circulating free fatty acids and glycerol Cholesterol comes from diet but mainly synthesised in liver from acetyl CoA Formation of bile Bile secretion Bile acid metabolism Bilirubin metabolism Bile secretion Bile consists of water, electrolytes, bile acids, cholesterol, phospholipids and conjugated bilirubin Two processed involved in bile acid secretion Bile salt dependent Bile salt dependent Bile salt independent Uptake of bile acids (and other organic/inorganic ions) across the basolateral (sinusoidal) by transport proteins – driven by NaK-ATPase in basolateral membrane Sodium and water follow passage of bile acids Bile salt independent Water flow is due to other osmotically active solutes e.g glutathione, bicarbonate Bile acid metabolism Bile acids are synthesised in hepatocytes from cholesterol Excreted into the bile and pass into duodenum Primary bile acids Cholic acid and chenodeoxycholic acid are conjugated with glycine or taurine which increases their solubility Secondary bile acids Primary bile acids converted by intestinal bacteria into deoxycholic and lithocholic acid Bile acids act as detergents – main function lipid solubilisation Have both hydrophobic and hydrophilic end and in aq solution aggregate forming micelles Bile acid metabolism Hormone and drug inactivation Major site for metabolism of drugs and alcohol Fat soluble drugs are converted to water soluble substances facilitating excretion in bile or urine Liver catabolises hormones e.g insulin, glycogen, oestrogens, growth hormone, glucocorticoids, parathyroid hormone Prime target organ for hormones e.g insulin Bilirubin metabolism Produced mainly from breakdown of mature red cells in Kupffer cells of liver and reticuloendothelial cells 15% bilirubin comes from catabolism of other haem containing proteins (myoglobin, cytochromes, catalases) Typically 250-300mg bilirubin produced daily Iron and globulin removed from the haem and reused Biliverdin is formed from the haem and is reduced to form bilirubin Bilirubin produced is unconjugated Bilirubin metabolism Uncongugated bilirubin Not water soluble Transported to liver bound to albumin Dissociates from albumin and taken up by hepatic cell membrane and transported to ER In ER is conjugated with glucuronic acid by bilirubin-uridyl diphosphate (UDP) Bilirubin metabolism Conjugated bilirubin Water soluble Secreted into biliary canaliculi reaching small intestine In gut bilirubin converted into urobilinogen (colorless) Most urobilinogen oxidised in colon to brown pigment stercobilin excreted in stool Some urobilinogen is absorbed from gut into portal blood and small amount excreted in urine Bilirubin metabolism LIVER INVESTIGATIONS Investigations Blood tests Liver function tests Liver biochemistry Viral markers Additional blood investigations; haematological, biochemical, immunological and genetic For bilirubin and urobilinogen Imaging techniques ALT/AST – reflecting hepatocellular damage ALP and GGT – reflecting cholestasis Total protein Urine tests Serum albumin Prothrombin time To define gross anatomy Liver biopsy For histology Liver function tests Serum albumin Marker of synthetic function Guide to severity of chronic liver disease Falling serum albumin is poor prognostic sign In acute liver disease albumin may be normal Prothrombin time (PTT) Marker synthetic function Short half life so sensitive indicator of both acute and chronic liver disease Vit K def should be excluded as cause of prolonged PTT Vit K def commonly occurs in biliary obstruction as low intestinal concentration of bile salts results in poor absorption of vit K INR often used as PTT varies in laboratories Hypoalbuminaemia Causes of hypoalbuminaemia Haemodilution Pregnancy, iv therapy, cirrhosis, antidiuretics Decreased synthesis Severe liver disease (chronic hepatitis, cirrhosis) Malabsorption, malnutrition Altered distribution Loss from the body Skin (burns, exudative lesions) Gut (protein loosing enteropathy) Increased catabolism Liver failure/cirrhosis Malignancy Malignancy Misc Acute/chronic illness, malignancy Hyperalbuminaemia Increased albumin Dehydration/haemoconcentration Venous stasis Healthy young adult Liver biochemistry Bilirubin Aminotransferases alanine amino transferase (ALT) and asparate amino transferase (AST) Alkaline phosphatase (ALP) Gamma glutamly transpeptidase Total protein Bilirubin and jaundice Yellow discoloration of tissues due to bilirubin deposition Clinical jaundice may not be clear until plasma bilirubin >50 umol/L First observed in sclera of the eye Laboratory investigation of Jaundice Classified on basis of other LFTs Isolated hyperbilirubinaemia High serum bilirubin only abnormality Unconjugated Conjugated Hepatobiliary disease High bilirubin accompanies other abnormalities in LFTs Laboratory investigation of jaundice Isolated hyperbilirubinaemia Increased production Haemolytic anaemias, hypersplenism, mechanical heart valves, resorption of haematomas, Decreased hepatic uptake Gilbert’s syndrome Drugs- Rifampicin, Testosterone, Sulphasalazine Decreased conjugation Gilbert’s syndrome Gallstones Further investigation Bilirubin fractionation FBC Haemolytic disease does not always produce low Hb High retic indicated high red cell production rate seen in haemolytic disease Lactate dehydrogenase Haemolytic disease and pernicious anaemia (megaloblastic anaemia) Associated with mild isolated hyperbilirubinaemia Reticulocytes Conjugated, unconjugated or mixed hyperbilirubinaemia Elevated in haemolysis, pernicious anaemia and hepatitis Haptoglobulin Bind to haemoglobin released in intravascular haemolysis causing low levels Gilberts syndrome Autosomal dominant (7% population) Bilirubin between 20 and 60 μmol/L Decreased conjugation especially during intercurrent illness or starvation Elevation <100 umol/L Measure Conjugated and unconjugated bilirubin Reflexed in lab on all GP requests when total bilirubin is over 30 umol/L and no other abnormalities >75 % unconjugated is consistent with Gilberts Syndrome Become jaundiced when unwell or fasting Reassure that no further tests are required Cholestatic jaundice Extrahepatic cholestasis Due to large duct obstruction of bile flow at any point in the biliary tract distal to the bile canaliculi Intrahepatic cholestasis Failure of bile secretion Pale stools and dark urine with conjugated serum bilirubin Transaminases ALT and AST are present in hepatocytes and leak into blood with liver cell damage Indicate hepatocellular damage AST Mainly mitochondrial and also present in heart, muscle, kidney and brain High levels seen in hepatic necrosis, MI, muscle injury and CCF ALT Cytosol enzyme More liver specific rise only in liver disease Released early in liver damage and remain elevated for weeks In hepatocelluar disease ALT rises before jaundice Cholestatic disease ALT may not rise Many labs only measure ALT as more specific than AST Levels of ALT Minor elevations (<100 U/L) Moderate elevations (100-300 U/L) Chronic hepatitis B and C Haemochromatosis Fatty liver Alcoholic hepatitis Autoimmune hepatitis Wilson’s disease Major elevations (>300 U/L) Drug toxins e.g. paracetamol Acute viral hepatitis Ischaemic liver Non-hepatic causes of elevated ALT Coeliac disease Muscle disease Strenuous exercise Alkaline phosphatase (ALP) Present in canalicular and sinusoidal membranes of liver Present in other tissues Bone, intestinal, placenta Normal situations bone and liver are the major isoenzymes If required, origin determined by electrophoretic separation of isoenzymes If elevated GGT, ALP can be presumed to come from liver Alkaline phosphatase (ALP) Raised in cholestasis from any cause (intra or extra hepatic) Synthesis of ALP is increased and realsed into blood Cholestatic jaundice levels may be 4XURL Raised levels also in conditions with infiltration of liver e.g metastases and cirrhosis often in absence of jaundice Highest levels due to liver disease seen with hepatic metastases and primary bilary cirrhosis Isolated mild rise in Alkaline Phosphatase Bone disease Paget’s disease Osteomalacia Healing fractures Metastases Hyperparathyroidism Vitamin D deficiency Drugs Anti epileptics Pregnancy Growth Children and teenage growth spurt Biliary disease Primary biliary cirrhosis (AMA positive) Other investigations with elevated ALP Further investigation may include Calcium and phosphate VitD and PTH Liver enzymes PSA Electrophoresis Isoenzymes Radiology GGT Microsomal enzyme present in many tissues as well as liver Activity can be induced by drugs e.g phenytoin and alcohol If ALP normal a raised GGT good guide to alcohol intake Mild elevations in GGT is common even with small alcohol consumption and doesn’t mean liver damage if other liver biochemistry normal In cholestasis GGT rises in parallel with ALP Isolated rise in Gamma GT Only measure to clarify raised alkaline phosphatase or DVLA fitness to drive Alcohol (although not always) Drugs Anticonvulsants, NSAIDs, antibiotics, antifungals, cytotoxics, testosterone Non alcoholic fatty liver Congestive cardiac failure Afro-Caribbeans have higher reference range Main use to identify source of ALP cheaper the ALP isoenzymes Other liver function tests Total proteins Measurement alone is of little value Globulin fraction calculated Elevated globulin fraction is liver disease is usually polyclonal due to increased circulating immunoglobins (rather than monoclonal in myeloma) Viral markers Viruses are major cause of liver diease Virology investigations are often key in diagnosis e.g. hepatitis Additional blood investigations Biochemical Alpha1 antitrypsin Deficiency can produce cirrhosis Alpha fetoprotein Normally produced by fetal liver Reappearance in high conc indicates carcinoma Serum and urine copper Wilsons disease hepatocellular Additional blood investigations Immunoglobulins Increased serum immunoglobulins Due to reduced phagocytosis by sinusoidal and Kupffer cells of antigen from the gut Antigens then stimulate antibody production Immunoglobulins (not produced by liver) Polyclonal elevations in chronic liver disease IgM elevated in primary biliary cirrhosis (PBC) IgA elevated in alcoholic liver disease IgG increased in autoimmune liver disease Additional blood investigations Autoantibodies Anti mitochondrial Antibodies (AMA) Found in serum in >95% patients primary biliary cirrhosis Nucleic, smooth muscle, liver/kidney microsomal antibodies High titre in autoimmune hepatitis Also in other autoimmune conditions e.g. SLE and liver disease Other tests Genetic analysis HFE in haemochromatosis Copper transporting ATPast in Wilsons disease Urine tests Bilirubin not found in urine in health Bilirubinuria is due to presence of conjugated (soluble) bilirubin Found in jaundiced patient with hepatobilary disease Absence implies that jaundice is due to increased unconjuated bilirubin Urobilinogen Little value but suggests haemolysis or hepatic dysfunction of any cause Imaging techniques Ultrasound (USS) Computed tomography (CT) Magnetic resonance imaging (MRI) Plain X ray of abdomen Endoscopy Liver biopsy Histological examination of liver used in the differential diagnosis of diffuse or localised parenchymal disease Can be done day case Mortality rate <0.02% in good hands Guided by US or CT when specific lesions need to be biopsied Minor complications Usually in first 2hrs Abdominal or shoulder pain Minor bleeding Major complications Major bleeding Sepsis Symptoms of liver disease Acute liver disease May be asymptomatic Symptomatic (usually viral) produces generalised symptoms of malaise, anorexia ad fever Jaundice as illness progresses Chronic liver disease May be asymptomatic or complain of non specific symptoms esp fatigue Specific symptoms include Right hypochondrial pain due to liver distension Abdominal distension due to ascites Ankle swelling due to fluid retention Haematemesis and melaenia due to GI haemorrhage Ithcing due to cholestasis Gynaecomastia, loss libido and amenorrhoea due to endocrine dysfunction Signs of liver disease Acute liver disease Few signs apart from jaundice and enlarged liver Cholestatic phase Pale stools and dark urine Spider naevi and liver palms may occur Chronic liver disease May be normal in advanced disease Skin Abdomen Chest and upper body may show spider naevi Hands show palmar erythema Xanthomas Hepatomegaly will be followed by small liver in well-established cirrhosis Splenomegaly seen in portal hypertension Endocrine system Gynaecomastia and testicular atrophy Signs of liver disease Session 2 LIVER CASES Case 1 AW (1) Age 48 male Hairdresser Painful joints Exhaustion Low libido AW (2) On examination pigmented ALT 167, ALP 175, GGT 147 Alb 43, BR 7 USS = hepatosplenomgaly. No varices AW (3) Viral studies negative Auto-antibodies negative α1-AT normal TSH 1.05 AW (4) Ferritin 5740 (rpt 6540) Testosterone 1.1 (n>10) Fasting Glu 9.7 Cortisol 612; prolactin 144; LH 3; FSH 3 IGF1 53 (n94-252); GH 0.12 Homozygous for C282Y Rx venesection, testogel liver biopsy (Jan 2009) = cirrhosis Iron Overload Syndromes Primary overload Secondary overload Others Iron loading due to liver disease Normal Iron Homeostasis in Humans Pietrangelo A. N Engl J Med 2004;350:2383-2397 Hereditary Haemochromatosis Type 1 Type 2a Type 2b Type 3 Type 4 Classical HFE Juvenile HH (Hemojuvelin) Juvenile HH (Hepcidin) TfR2 mutations Ferroportin HFE related Haemochromatosis C282Y mutation in HFE gene Autosomal recessive Mechanism complex/unclear Excess duodenal iron absorption leads to deposition in specific organs Frequency of HH 1 in 5000 ‘bronze diabetes” 1 in 200 N Europeans homozygous C282Y 1 in 9 carriers for C282Y Commonest autosomal genetic disorder in caucasians ??? Haemochromatosis (3) Often middle age More males 80% fatigue 56% abdo pain 45% arthralgia (2nd + 3rd metacarpals) 37% loss of libido Complications of HH Diabetes Joint symptoms Cardiac disease Skin pigmentation Impotence Sites of iron deposition Skin Liver Pancreas Endocrine (ant pit, rarely thyroid, adrenal) Myocardium HFE-Related Hereditary Hemochromatosis, a Multistep, Multifactorial Iron-Overload Disorder Pietrangelo A. N Engl J Med 2004;350:2383-2397 How to diagnose? Detection of HH Transferrin saturation (>45%) Ferritin (?) HFE genotype C282Y homozygote C282Y + H63D (4%) (Liver biopsy) (MRI) How to treat? Therapeutic Venesection Aim for ferritin 50-100 (satn<30%) Weekly to fortnightly Improves fatigue LFTs diabetic control arthropathy If fit can go to blood donation once ferritin down Endoscopy Unit Who to biopsy? HH with ferritin >1000 40% risk of cirrhosis HH with ferritin <1000 cirrhosis very unlikely Further Management Rx diabetes Testogel etc Bone density FU for cirrhosis Family screening Learning Points HH is common HH is usually easy to diagnose HH is easy to treat Early treatment prevents “disease” Think: iron overload Case 2 3rd July 47 year old female Called ambulance 26 hours after taking a paracetamol overdose Seen at 22:00 The patient (1) Suffers from depression due to physical pain and death of mum in 2008 Took overdose of approx. 50g paracetamol (100 tablets) at approx. 20:00 on 2nd July 08 Taken on empty stomach The patient (2) Started vomiting at 23:00 which made her regret her actions Started feeling cold and sweaty at 18:00 on 3rd July 08 Impulsive O/D following an argument with son No further suicidal thoughts or plans Initial assessment, 3rd July No suspicion of alcohol or illicit drugs Airway clear and respiratory rate 20/min (normal: <8-25/min)Temperature of 36.7oC Bp: 154/112 (normal: 127/85) Heart rate: 116 (normal: 54-83) Glasgow coma score (15/15) Alert Quite nervous Other conditions in patient Osteoarthritis Fibromyalgia Rheumatoid arthritis Depression Past drug history Pain killers Fentanyl Transdermal Patches Naproxen E/c Tramadol m/r Paracetamol 500mgs (8 per day) Antidepressants Amitriptyline Sertraline Arthritis drugs Alendronic Acid Calcichew-D3 Folic Acid Hydroxylchloroquine Sulphate Prednisolone E/c Paracetamol poisoning <24h Anorexia, nausea and vomiting 24 – 48h Abdominal pain, hepatic tenderness, prolonged PT, elevated plasma aminotransferases and bilirubin >48h Jaundice, encephalopathy, renal and hepatic failure Paracetamol poisoning No immediate effect after O/D The PT is the best marker of severity The likelihood of a liver damage can be predicted from the plasma concentration of paracetamol, which also helps with the determination of appropriate decisions for antidotal therapy ALT indicates severity of overdose Treatment options Antidote of choice is N-acetylcysteine (intravenous) Methionine (oral) 5% dextrose (for hydration) Liver transplantation may be appropriate in the most severe cases Patient Investigations Liver function tests Total protein Albumin Bilirubin ALT (Aminotransferase) ALP (Alkaline Phosphatase) Clotting screen INR (International Normalised Ratio) Patient results 3rd July BLOOD COUNT Haemoglobin 15.1 g/dl White cell count 13.6 109/L Platelet count 386 109/L (normal value) 12 – 16 3.9 – 11.1 150 – 450 LFT (liver function test) TP (total protein) 85 g/L Albumin 44 g/L ALP 78 u/L Total bilirubin 29 umol/L ALT 3533 u/L 60 – 80 35 – 50 30 – 130 0 – 20 5 - 65 FULL CLOTTING SCREEN PT 15.1 secs INR 1.3 APTT 29.5 secs 10.2 – 13.3 0.8 – 1.2 27.8 – 36.3 PARACETAMOL paracetamol 30 mg/L Treatment DATE INFUSION FLUID VOLUME DRUG DOSE DURATION 3/7/08 5% DEXTROSE 200ml N-acetylcysteine 20000mg 15mins 3/7/08 5% DEXTROSE 500ml N-acetylcysteine 6000mg 3/7/08 5% DEXTROSE 1000ml N-acetylcysteine 13000mg 16hourly 5/7/08 5% DEXTROSE 1000ml N-acetylcysteine 11g 16hourly 5/7/08 5% DEXTROSE 1L N-acetylcysteine 11g 16hourly 4hourly N-acetylcysteine Paracetamol is metabolised in the liver, mainly by conjugation with glucuronide and sulphate to form a reactive, potentially toxic, metabolite In paracetamol overdose, the glucuronide and sulphate conjugation pathways are saturated, so that more of the toxic metabolite N-acetyl-pbenzoquinoneimine (NAPQI)is formed N-acetylcysteine Acetylcysteine protects the liver from damage by restoring depleted hepaticreduced glutathione levels, or by acting as an alternative substrate for conjugation with, and thus detoxification of, the toxic paracetamol metabolite. Results 6th July BLOOD COUNT Haemoglobin 13.4 g/dl White cell count 9.9 109/L Platelet count 386 109/L (normal value) 12 – 16 3.9 – 11.1 150 – 450 LFT (liver function test) TP (total protein) 72 g/L Albumin 38 g/L ALP 62 u/L Total bilirubin 12 umol/L ALT 1472 u/L 60 – 80 35 – 50 30 – 130 0 – 20 5 - 65 FULL CLOTTING SCREEN PT 14.7 secs INR 1.2 APTT 27.0 secs 10.2 – 13.3 0.8 – 1.2 27.8 – 36.3 PARACETAMOL paracetamol <10 mg/L ALT Results Results INR Results Results Outcome Reviewed by psychiatrist Medically fit for discharge (after review of anti-depressant therapy) Referral for bereavement counselling Discharged Thoughts of taking O/D again Finally She had a lucky escape Paracetamol poisoning is a very slow and agonizing process of death Case 3 SW Female Age 69 Retired secretary November 2009 short of breath for 3-4 weeks on exertion (step aerobics, dog walking) Hb 10.2 No recent loss of weight, blood loss, melaena or altered bowel habit Microcytic anaemia Results from GP 12/11/09 Hb WBC Platelets MCV Ferritin 8.2 5.9 213 99.4 95 Referred by GP to A&E Na K Urea Creat TP Alb Glob Alk phos Bilirubin ALT 140 Haemolysed 11.1 152 69 44 25 47 67 Haemolysed A&E results 12/11/09 16:28 hours, jaundiced anaemic dehydrated Hb 8.0 WBC 5.9 Platelets 213 Na K Urea Creat Bili ALT What tests would you do now? 137 Haemolysed 11.4 165 68 Haemolysed Results over next few days Date 9.12 9.12 10.12 12.12 14.12 15.12 16.12 Hb 8.0 8.0 7.6 7.4 7.2 8.9 9.1 K H H H H H H H Urea 11.3 11.4 10.0 7.7 8.0 7.7 7.1 Creat 163 165 143 129 123 125 131 Bili 67 68 61 39 50 49 36 ALT H H H H H H H What do you make of these? What other tests would you do? Clinical History Hypothyroidism Hysterectomy Psoriasis Mitral valve replaced 1988 and 1994 Aortic valve replaced 1994 Hypertension Left hip and right knee replaced due to OA Perforated peptic ulcer Drug therapy Thyroxine 125 ug Candesartan 8mg OD Warfarin 5mg/ 4mg Other results Conjugated/ unconjugated bilirubin Haemolysed LDH 5450 IU/L Haptoglobin <0.3 g/l B12 282 Folate Haemolysed Ferritin 277 Serum appearance noted by Biochemistry Other results Reticulocyte count Blood film Direct Coombes test Hep B/ Hep C ANA, ANCA 15.5 % Negative Negative Haemolysed Blood film Red cell fragments and polychromasia with occasional nucleolated red cells Burr cells Acanthocytes Schistocytes Consistent with mechanical haemolysis from prosthetic heart valves Additional tests •Direct Coombe’s test Haptoglobin Protein which binds to free haemoglobin in the blood Acute phase protein Complex removed by spleen Low result indicates intravascular haemolysis Methaemalbumin Haemoglobin is converted to Haematin which is then bound to albumin-brown pigment Further course Another 20 U&Es done with no potassium available due to haemolysis Transfused ECHO showed para prosthetic mitral regurgitation from 20% of surface. Referred to Essex CTC for mitral valve replacement then to UCLH In May vegetation on valve so not operated on RIP May 2010 Haemolytic anaemia Due to breakdown of red blood cells (normally 1% break down each day, removed by spleen) Intravacular Extravascular Inherited or acquired Lab tests required Haemoglobinopathy screen if indicated Film and direct Coombe’s test, reticulocyte count Conjugated bilirubin, LDH and haptoglobin Treatment depends on the cause Transfusion Steroids or Rituximab Bone marrow transplant Splenectomy Avoiding triggers Inherited causes Defects in Hb production Thalassaemia Sickle cell Haemoglobinopathies Defects in red cell membranes Hereditary Hereditary spherocytosis ellipsoidosis Defects in red cell metabolism G-6-PD deficiency Pyruvate kinase deficiency Paroxysmal nocturnal haemoglobinuria Acquired haemolytic anaemia Immune mediated causes AIHA or CHAD Hypersplenism Aquired Burns, infections Toxins Lead, fava beans Drugs Penicillin, anaesthetics, antimalarials, Dapsone in succeptible patients, Transfusion reaction/ rhesus incompatability Physical destruction mechanical heart valves, heart-lung machines Footstrike haemolysis Mechanical heart valves Mitral valve Mechanical Stented or open surgery Last indefinitely Lifelong treatment with anticoagulants Damage red cells Biological Allograph or xenograph (pigs) Only last 15 years No anticoagulation required Do not damage red cells