Biochemistry Lecture #3

Transcription

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2 Hello Awn.. This lecture includes the slides.. anything with (!) is important.. and Italic line Any sentence within Double Brackets {{ }} is just for understanding (Not from Slides) Let s start with this easy lecture Today s lecture will be about Liver Function Tests (LFTs): We will start with a case to see how important the LFTs are: 75 years old Female Presented to the *General Practitioner complaining of Dyspepsia and Back pain The background History: She had breast cancer which was treated with mastectomy, and she s on Tamoxifen an Anti-cancerous Drug, Variegate Porphyria {{ which is an inherited disease that affects one of Heme s biosynthetic enzymes }}, Type 2 Diabetes Mellitus And Subclinical Hypothyroidism. *GP requested LFT, and the results came : Albumin 43 (34-48) g/l Total Bilirubin 7 (0 21) µmol/l Alkaline Phosphatase 67 (35-104) IU/L GGT 93 (5 36) IU/L ( gamma-glutamyl transferase ) Alanine Transaminase (ALT) 40 (6 31) IU/L Normal Normal Normal Slightly Elevated Slightly Elevated Now, when the doctor saw her LFT which was Almost normal except for the GGT and ALT he ordered further investigations which are a little specialized ones : - Anti Smooth Muscle Abs (ASMA) - negative - Anti Mitochondrial Abs (AMA) - negative - Alpha-1 Antitrypsin : 1.5 ( ) g/l - Ceruloplasmin: 26.2 (20 60) mg/dl - Transferrin Saturation : 34% (15 45) % بتعرفو مش هيك - Prothrombin time : 14.8 ( ) s - Activated Partial Thromboplastin time : 30.4 s (25 35) s And All of them were Normal so we are left we these slightly elevated tests which are ALT And GGT 2 P a g e

3 So, further investigations are ordered (Imaging Studies) in view of negative blood tests: - Ultrasound of Abdomen And Pelvis: Liver: diffuse inhomogeneous somewhat echogenic texture, No focal lesion, Bile Ducts Not Dilated. ( Normal ) - CT Scan Of Abdomen : Liver: Normal Size, Subcapsular surface of the liver has a nodular outline, Liver texture has a diffuse slightly coarse appearance. ( Now These Are Consistent With Liver Cirrhosis ) Note : The only indicator for the presence of underlying cirrhosis in this patient were her mildly abnormal LFTs, So Pay Attention To mild Elevations! Now.. Easy Question What are the Functions of the liver? 1. Great Rule In Metabolism. (e.g. gluconeogenesis, glycolysis, ketogenesis, lipid synthesis) 2. Protein synthesis. (including many plasma proteins and blood clotting factors) 3. Bile secretion and role in digestion 4. Primary site of Xenobiotic Detoxification (drug and toxin metabolism) 5. Ureagenesis ( Role in acid-base balance ) Now For The Main Concept of this lecture : Liver Function Tests Total Bilirubin : Two Types : Conjugated vs. Unconjugated. Alkaline Phosphatase : - Reference range varies with age > Higher in childhood {{ Because of higher Metabolism }} vs. adolescence. - Isoenzymes : e.g. bone, liver, intestine, malignancy ( Not Only In Liver! ) - Bile flow. Gamma-Glutamyl Transferase : - Sensitive indicator of liver disorder. - Cholestasis. - Induced by many drugs and toxins e.g. C2H5OH ( Alcohol ) (Drugs) : phenytoin, Barbiturates and <possibly> statins. Transaminases: ( Amino Acid Metabolics ) - Alanine Aminotransferase (ALT) - Aspartate Aminotransferase (AST) - Both are specific to liver BUT ALT is more specific Than AST! And we usually look at the Ratio : AST / ALT. 3 P a g e

4 - AST is also found in cardiac and skeletal muscle. - These enzymes are INDICATORS of Hepatocellular Integrity because they are intracellular, usually we don t see them in plasma or blood but when there is damage to the hepatocytes we can see them. Albumin: Plasma Transport Protein, Assess protein synthesis in liver. Prothrombin Time: Extrinsic Pathway of coagulation, Reflects Protein synthesis in the liver. What Are #the Roles of LFTs in clinical Management? Detecting the presence of liver diseases. Indicating the broad diagnostic category of the liver disease. Diagnose to Monitor treatment, because if you put a patient on a toxic drug e.g. Phenytoin you have to monitor his liver functions. Also we have #specialized Liver Function Tests: Viral Hepatitis Screen A, B, C etc. Autoimmune Hepatitis screen AMA (antimitochondrial antibody), ASMA (Antismooth muscle antibodies) Serum protein electrophoresis α1- antitrypsin α fetoprotein (AFP) Transferrin Saturation, Ferritin, HFE Genotyping which is a gene for: (hereditary hemochromatosis) Ceruloplasmin, Plasma, Urine Copper Ultrasound scan, CT, MRI Biopsy Now when you re about to order LFT you should take history from the patient: 1. Ethanol Consumption C2H5OH because it s highly toxic to the liver. 2. Family History because of certain hereditary diseases(hemochromatosis) 3. Drug History, Which were mentioned earlier. 4. Travel History, to Areas with epidemics. 5. Blood transfusion History? ( HCV HIV ) 4 P a g e

5 Now For the Process of degradation of Heme which we all know about :P *I hope this figure is clear and the doctor simply read it: ( > means then ) Haemoglobin is broken down by Reticulo-endothelial System >Unconjugated bilirubin is transferred to the liver carried by the albumin > the process of bilirubin conjugation By 2 molecules of Glucoronic-Acid are added. UDP Glucoronosyl-transferase > production of Bile and excretion into the intestine > conversion into Urobilinogen > Stercobilin will go with feces > some of Urobilinogen will be excreted through the kidney So the process of conjugation is important when we tests to determine conjugated vs. unconjugated bilirubin if it s from liver disease or not as we will see : Hyperbilirubinaemia Jaundice evident with Bilirubin levels μmol/l. ( Normal: <22 μmol/l ) Normally 95% of plasma bilirubin is unconjugated. Hyperbilirubinaemia is of 3 Causes : Unconjugated pre-hepatic 1 *(No bilirubinuria): Hemolysis. Resolving hematoma. That s been dissolving Gilbert s Syndrome. Crigler-Najjar syndrome. 5 P a g e

6 Conjugated Hepatic 2 /posthepatic 3 (Bilirubinuria) in constriction of secretion Hepatocellular diseases Cholestatic diseases Dubin-Johnson** {{ Autosomal Recessive disorder, increases CONJUGATED bilirubin without interfering with liver enzymes, and usually Asymptomatic }} Rotor s syndrome** {{This disease shares many features with the previous one, BUT an exception for that is that the liver cells in this one are NOT pigmented}wiki **These two diseases will result in Benign congenital conjugated hyperbilirubinemia. *(No bilirubinuria from prev page):except in Nephrotic Syndrome 6 P a g e if we take a look at this figure we can see an increased production, when? Heamolytic Anemia: excessive Destruction > Excessive Bilirubin. -Impaired Hepatic Uptake: Toxins or Viral. -Impaired Secretion: When we say post hepatic that means that there is obstruction in the excretion Could be : -intrahepatic: cirrhosis and infiltration -posthepatic: gallstones.. *If we have a damage to the hepatocytes we will see increase in both conjugated and Unconjugated bilirubin... Gilbert s Syndrome : Disease that causes elevation of Unconjugated bilirubin. - Present in 5% of the population. Pretty common - Males > females. - Genetic origin : insertion of Tail Anchored (TA) protein in promoter region of UGT-1A gene ( UDP-Glucoronosyl-transferase 1).

7 - Exacerbated by fasting and illness. - Confirm Unconjugated hyperbilirubinemia. - Rule out hemolysis CBC, Reticulocyte count. when you do differential diagnosis you rule out these diseases - Rule out underlying liver disease. Now we all know about Neonatal Jaundice, Most babies have jaundice because of the destruction of fetal Hemoglobin, if it reaches a high level then this will cause a problem: Unconjugated bilirubin level > 300μmol/L may be associated with Kernicterus (brain damage due to uptake of unconjugated bilirubin) in the normal process fetal haemoglobin will be replaced by adult haemoglobin and the levels are within the acceptable range The other causes are listed in this table and the doctor read them all Hepatocellular Now the #Patterns LFTs: Predominant elevation in AST/ALT ratio*: {{ 2:1 or greater is suggestive of liver disease }} *Both enzymes require pyridoxal-5'-phosphate (vitamin B6) in order to carry out this reaction, although the effect of pyridoxal-5'-phosphate deficiency is greater on ALT activity {{that s why it is more specific!}} than on that of AST. This has clinical relevance in patients with alcoholic liver disease, in whom B6 deficiency may decrease ALT serum activity and contribute to the increase in the AST/ALT ratio that is observed in these patients. 7 P a g e

8 Cholestatic Predominant elevation in ALP (alka.phosph) with GGT ± Bilirubin Note: Bilirubin could be elevated and could be normal..but in cholestatic ALP and GGT are always elevated Mixed Elevation in both AST/ALT, and ALP/GGT ± Bilirubin #Causes of a Hepatocellular Pattern of LFTs: Marked elevations in ALT/AST > X5 : (patient likely to be Symptomatic!) if the elevation is X2 it s mild, X3 it s moderate, however X5 is called MARKED -Viral hepatitis A,B,C in Acute form. -Ischaemic hepatitis. -Autoimmune hepatitis. -Drug/toxins e.g. alcoholic hepatitis! Pay Attention! Mild/Moderate elevations in ALT/AST < X5 : (patient may be Asymptomatic!) - Chronic Hepatitis - ALD (Adrenoleukodystrophy), Beta Oxidation of fatty acids disorder ( metabolic pathway that breaks down fatty acids for energy production ) - *NAFLD/NASH (Nonalcoholic fatty liver disease /Non-alcoholic steatohepatitis): *associated with obesity, T2DM, Hyerlipidemia - Metabolic liver diseases: Hereditary Hemochromatosis (HH), Wilson Disease, Alpha-1 antitrypsin deficiency. - Drugs. - Autoimmune Liver Disease. 8 P a g e

9 Now, How to approach an Asymptomatic patient with ALT/AST Ratio: Elevated AST/ALT Repeat Test(for conformation) Muscle Problem Normal Still Elevated Send Patient home Check CK Elevated? Normal? Drug History etc More Likely to be Liver Etiology so we start our investigations -Viral Serology -Autoimmune(AI) hepatitis screen -Fe/TIBC(Total iron binding capacity)/hfe(hemochromatosis Gene) Genotyping -Ceruloplasmin if patient is < 40 Years old. -Alpha-1Anti Trypsin (AAT) deficiency. -Celiac Screen. -Ultrasound Scan Other Investigations: -MRI/CT -Bx (doctor said barium but i think it s biopsy) 9 P a g e

10 #Causes of Cholestatic Patterns of LFTs: As we said in this case we ll see Elevated ALP and GGT ± Bilirubin, relative to transaminases, it s divided into intra-hepatic 1 and Extra-Hepatic 2 : * Intrahepatic 1 : (Bilirubin Not elevated) * Extrahepatic 2 :(Bilirubin elevated) -Medications -TPN (Total Parenteral Nutrition) -Sepsis -Postoperative -PBC (Primary Biliary Cirrhosis) -Alcoholic hepatitis -Liver metastasis -Pregnancy-related -CCF (Congestive Cardiac Failure) -Cholelithiasis (CBD) -Malignancy -Primary sclerosing cholangitis Note: GGT is useful in differentiating Liver as a cause of elevated ALP!imp But why?!: because we said that Alkaline Phosphatase have many isozymes and it could be of Non-liver origin so we pay attention to GGT more than ALP.. *so now we have ALT and GGT both are more liver specific please memorize this.. Now, An approach to the patient with isolated elevation in ALP(only ALP is elevated) Elevated ALP? Now if there is NO abnormalities: we look for -Primary Biliary Then this is Normal? Check GGT Cirrhosis By doing: Anti- A Non liver cause Mitochondrial antibodies Could be: bone,placenta, Elevated? 3 -and you consider another The intestine, etc.. causes maybe medication and We do further studies order further investigations 1 Like: US,MRI,CT Biliary dilation 2 Focal mass? 10 P a g e

11 #By now we ve talked about Specialized and Non-Specialized LFTs but we have kman shwi lsa :P Serum ammonia: #Other LFTs : (little important informations) -Used for investigation of Hepatic Encephalopathy.! (because Ammonia highly toxic to brain CNS if in high levels) -Lacks sensitivity and specificity for the liver and it could be of Non-liver Origin. -Useful for investigation of urea cycle disorders.(if ammonia is elevated طبعا كلنا عارفينو cycle) Most probably there s a problem with urea Serum LDH: (Lactate Dehydrogenase) -Included in LFTs -5 isoenzymes heart, erythrocytes, skeletal muscles, liver, others. -Not Specific for the liver. -it displays abnormalities in ischemia-related liver diseases. -useful in monitoring certain malignancies e.g. B-cell lymphoma - not really a LFT ( the doctor said that it was a cardiac marker, but now b76oh 3l-rf.. same As Guyton w hdol el sh3 lat :P). Now for the #Reference Ranges we asked the doctor about the numbers and he said that they are not for memorizing, I ll write what he said about them: You should be familiar with these, Albumin Bilirubin g/l <17 mmol/l *Note: ALP is age related, it s always higher in ALP* AST ALT GGT IU/L* 7-40 IU/L 7-35 IU/L IU/L children, why is that? Because of higher metabolic and catabolic processes in children!. ALT and AST are pretty much the same. 11 P a g e

12 #Paracetamol Overdose: Now, Drugs are toxic to the liver, and one of the highly abused drug is Paracetamol or Acetaminophen.. why? L2no mna5do mtl el bnbon.eza ma fhmt 3adi :P The doctor mentioned it as Telenol, and it puts a lot of stress to the liver, so hepatic Necrosis could be seen from Paracetamol Note 1 : Hepatic Necrosis observed within hours (within 3 days), some people who drink and become hangovers next morning they will have headache and take paracetamol!, but it will worsen the situation on the liver and they will have liver damage faster than others! Note 2 : toxicity is caused by accumulation of breakdown product *NAPQI, It consumes most of the Cytochrome P-450. And it will lead to cell death. Paracetamol Sulphation Cytochrome p-450 Glucuronidation *N-acetyl-β-Benzoquinone Imine +glutathione + Nucleophilic cell Macromolecules Mercapturic Acid Cell Death Now for a patient who comes with toxicity: Antidote? Yes:N-acetylcysteine (Parvolex) is an effective agent. Note: Ideally before 12 hours post ingestion. ( the more delay the more irreversible damage to the liver..) And By that you ve ended the Final Lecture in this system my friend.. eb2a 2ablni b3d el imti7an Best of luck to you All 12 P a g e