BACHELOR OF MEDICINE AND BACHELOR OF SURGERY UNIT CODE: MBMB2200 UNIT TITLE: MEDICAL BIOCHEMISTRY II (MBMB2211A: Tissue Metabolism and Integration of Metabolis
BACHELOR OF MEDICINE AND BACHELOR OF SURGERY UNIT CODE: MBMB2200 UNIT TITLE: MEDICAL BIOCHEMISTRY II (MBMB2211A: Tissue Metabolism and Integration of Metabolism MBMB2211D: Clinical Biochemistry) UNIVERSITY EXAMINATION 2021/2022 DEPARTMENT OF MEDICAL BIOCHEMISTRY DATE: TIME: 2 HOURS GOOD LUCK DAKTARI Sample Handling in Clinical Diagnosis Explain the Concept of Sample Handling in Clinical Diagnosis (5 Marks) Definition: Collection, processing, and storage of biological specimens to ensure accurate laboratory results. --- 1. Blood Sample Types & Additives (1 mark) - Serum (clotted blood) → no fibrinogen - Plasma (anticoagulated) → contains fibrinogen - Heparin - blocks clotting factors - EDTA/Citrate - bind Ca²⁺ - Note: Use serum for Na⁺, K⁺, Li⁺ (anticoagulants interfere) --- 2. Special Tubes (1 mark) - Fluoride tube → glucose (stops glycolysis) - Urine additives: Azide/toluene → prevent bacteria - HCl → Ca²⁺, Mg²⁺, phosphate(prevents precipitation). - Alkaline → urate --- 3. Avoid Contamination (1 mark) - No drip arm sampling - Correct tube selection - Proper labeling --- 4. Timely Separation (1 mark) - Separate within 12 hours - Delayed = false high K⁺, phosphate, LDH - Hemolysis → red serum --- 5. Labile Analytes (1 mark) - Blood gases → anaerobic + ice to prevent gas loss and lactic acid formation. - Peptide hormones → protease inhibitors - Ammonia → immediate analysis due to glutamine breakdown --- Key Points: Time-sensitive processing essential Proper handling = accurate results Wrong technique = wrong diagnosis Definition: - These are the ranges of values from which the clinical parameters are measured from Significance: - Aid in diagnosis – Compare patient results to normal limits. - Monitor treatment – Track changes during therapy. - Detect disease early – Identify abnormalities before symptoms appear. --- --- Preanalytical Phase – Key Steps (Short Notes) - Preparation for Collection Patient instructions: diet, posture, urine containers . - Sampling Preparation Test request , data entry, and tube labeling . - Sampling Patient ID , timing, tourniquet use, site & needle positioning, tube changes. - Transport Prompt collection and safe transport to lab. - Sample Treatment Registration, centrifugation , mixing, and sample extraction . - Storage Control of storage time, temperature , and remixing before use . --- --- Explain Ways to Detect Systematic Errors (4 Marks) - Method Comparison Compare results from two different analytical methods ; significant differences suggest a systematic error. - Standard Value Comparison Compare experimental result with a known standard value ; deviation indicates possible error. - Use of Blank Solution Run a blank (no analyte). If it gives a reading, subtract it from the result to correct for systematic error. - Inter-Laboratory Testing Analyze same sample in different labs or by different analysts ; consistent differences suggest systematic error. --- o Unlabelled sample o Mislabeled sample – any mismatch or discrepancy of identification o Insufficiently labeled sample – less than two identifiers o Transfusion labeling requirements – no collector signature, no time and date of collection o Sample suspected to be from wrong patient – wrong blood in tube Causes of Low Total Protein in Blood - Liver disease – the liver makes most blood proteins. - Poor diet (malnutrition) – not enough building blocks to make proteins. - Too much water in blood (haemodilution) – proteins get diluted. - Loss of key proteins – like albumin or antibodies (globulins). ( hypoalbuminaemia or hypogammaglobulinaemia .) Examples of Tumor Markers: - Enzymes – general, not specific to one cancer type. - Acid Phosphatase – seen in prostate cancer . - Alkaline Phosphatase – associated with bone and liver cancers . - Prostate Specific Antigen (PSA) – specific for prostate cancer . - Alpha-Fetoprotein (AFP) – marker for liver cancer . - Immunoglobulins – elevated in plasma cell cancers (e.g. multiple myeloma). - Carbohydrate Antigen 125 (CA-125) – seen in ovarian cancer . - Carbohydrate Antigen 15-3 (CA 15-3) – used in breast cancer monitoring. - Isoenzyme Analysis : Separate enzyme isoforms to identify the specific tissue source. - Use of Specific Inhibitors : Apply enzyme inhibitors that target particular isoenzymes, improving specificity. - Glycolysis :Main energy source, anaerobic. - Glucose → 2 ATP and lactate (no mitochondria). - Hexose Monophosphate Shunt (Pentose Phosphate Pathway) :Produces NADPH to protect against oxidative stress. - Maintains cell integrity. - Lactate Production :Final product of glycolysis. - Transported to liver (Cori Cycle) to produce glucose. - No Mitochondria : Erythrocytes cannot perform oxidative phosphorylation, relying solely on glycolysis for ATP. - Bilirubin Metabolism : Heme → Biliverdin → Bilirubin → Conjugated in liver → Excreted as bile. - Unconjugated : Bound to albumin (not water-soluble). - Conjugated : Water-soluble, excreted in bile. - Disorders : Jaundice : Yellowing of skin/sclera. Pre-hepatic (Hemolytic) : Excess RBC breakdown. - Hepatic : Liver dysfunction (e.g., hepatitis). - Post-hepatic (Obstructive) : Blockage in bile flow (e.g., gallstones). - Gilbert’s Syndrome : Mild, reduced conjugation (asymptomatic, mild jaundice under stress). - Crigler-Najjar Syndrome : Severe conjugation deficiency, high unconjugated bilirubin (risk of brain damage). - Dubin-Johnson Syndrome : Impaired excretion of conjugated bilirubin, mild jaundice. - Clinical Tests : Total Bilirubin : Conjugated + Unconjugated. - Direct Bilirubin : Conjugated. - Indirect Bilirubin : Unconjugated. others Bilirubin Metabolism : Bilirubin is a breakdown product of heme , released from hemoglobin in aged red blood cells. Process : - Heme Breakdown : The heme group is first converted to biliverdin (green) by heme oxygenase , then biliverdin is reduced to bilirubin (yellow) by biliverdin reductase . - Transport to Liver : Bilirubin is transported to the liver bound to albumin in an unconjugated form (indirect bilirubin). - Conjugation in Liver : In the liver, UDP-glucuronosyltransferase conjugates bilirubin with glucuronic acid to form conjugated bilirubin (direct bilirubin), which is water-soluble. - Excretion : Conjugated bilirubin is excreted into the bile and stored in the gallbladder, eventually being excreted in the feces as stercobilin . A small amount is reabsorbed into the blood and excreted in urine as urobilinogen . Disorders of Bilirubin Metabolism : - Jaundice : A clinical manifestation of excessive bilirubin in the blood, resulting in yellowing of the skin and sclera. Jaundice can be: Pre-hepatic (Hemolytic Jaundice) : Due to excessive breakdown of red blood cells, leading to an overproduction of bilirubin. - Hepatic Jaundice : Caused by liver dysfunction (e.g., hepatitis, cirrhosis) that impairs conjugation of bilirubin. - Post-hepatic (Obstructive Jaundice) : Due to obstruction of bile flow (e.g., gallstones, tumors), preventing the excretion of conjugated bilirubin. - Gilbert's Syndrome :A mild, inherited disorder resulting in reduced conjugation of bilirubin due to a genetic deficiency in UDP-glucuronosyltransferase . - Clinical Significance : Often asymptomatic but can result in mild jaundice under stress, fasting, or illness. - Crigler-Najjar Syndrome :A rare genetic disorder characterized by a severe deficiency or absence of UDP-glucuronosyltransferase , leading to the accumulation of unconjugated bilirubin in the blood. - Clinical Significance : Can lead to kernicterus (brain damage) if untreated. - Dubin-Johnson Syndrome :An inherited disorder where there is impaired excretion of conjugated bilirubin due to a defect in the multidrug resistance protein 2 (MRP2) , which is responsible for transporting conjugated bilirubin into bile. - Clinical Significance : Results in conjugated hyperbilirubinemia and mild jaundice, but usually no significant long-term effects. Clinical Tests : - Total Bilirubin : The sum of conjug