Clinical Biochemistry Notes 11

Clinical Biochemistry: An Overview

Clinical biochemistry investigates the function and dysfunction of systems, organs, and tissues through the measurement of biochemical markers. This field is essential for understanding various physiological processes and disease states.

Key Areas in Clinical Biochemistry

The core areas include:

• Range of common methods used for collection and analysis of clinical samples.

• Investigations of major body and organ systems (e.g., renal function tests, liver function tests, tumor marker tests, and bone profile tests).

• Principles and applications of biochemical investigations used for screening, diagnosis, treatment, and monitoring of diseases.

• Therapeutic drug monitoring and investigation of substance abuse.

Types of Clinical Samples

Clinical biochemistry involves analyzing various samples:

• Blood (serum, plasma): Serum and plasma are not the same; their differences are significant in analysis.

• Urine: Used for assessing kidney function (e.g., potassium, sodium, creatinine, albumin).

• Cerebrospinal Fluid (CSF): Aids in differentiating between bacterial and viral meningitis based on glucose content.

• Stool: Used for fecal occult blood testing, which can detect colorectal cancer or bleeding in the intestines.

• Vitreous Humor: Fluid from the eye, used post-mortem to estimate the time of death by measuring sodium, potassium, and glucose levels.

• collection includes: Blood tubes used, order of tubes, patient identification transport.

Factors in Obtaining Correct Results

Several factors are critical for accurate results:

• Pre-analytical variables:

  • Technical: Correct patient identification, proper sample collection of the specimen, accurate labeling, rapid and secure transport.

  • Biological: Patient's age, gender(hormonal changes),Bmi changes due to ethnicity as well as build, body mass, origin, stress, posture, food intake, drugs, occupation and altitude.

• Analytical variables: Accuracy and precision of tests. time of day matters

• Post-analytical variables: Data interpretation and reporting.Transmission\Transcription of report.

Pre-analytical Variables

Technical Factors

• Patient Identification: Incorrect identification can lead to serious errors in diagnosis and treatment. For example, mixing up samples from two patients with similar names.

• Specimen Collection: Samples must be collected in the correct order to avoid contamination between different types of blood tubes. The order is crucial for the validity of results.

• Labeling: Accurate labeling is essential; improperly labeled samples are typically discarded to prevent incorrect diagnoses.

• Transport: Rapid and secure transport is crucial, especially for glucose samples, as glucose levels can change over time due to cellular consumption.

Biological Factors

• Age: Reference ranges for certain markers, like hemoglobin, vary with age.

• Gender: Men and women have different reference ranges for many tests due to hormonal and metabolic differences.

• Ethnicity: Certain reference ranges, like creatinine, vary among different ethnic groups. For example, black individuals tend to have higher creatinine levels.

• Body Mass: Reference ranges can vary based on an individual's body mass and muscle metabolism.

• Time-Dependent Changes: Some hormones, like cortisol and growth hormone, vary depending on the time of day, necessitating specific sampling times.

• Stress: Stress can influence hormone levels, like cortisol.

• Posture: Blood pressure and other measurements can change depending on posture.

• Food Intake: Diet can affect blood levels of certain substances, like B12 and folate.

• Drugs: Medications can impact various blood results.

• Occupation: Night shift work can affect hormone levels.

• Altitude: Training at high altitudes affects red blood cell production.

Analytical Variables

Accuracy and Precision

• Accuracy: How close a measurement is to the true value.

• Precision: How consistent a measurement is.

• For clinical tests, precision is often more valued because consistent results allow for better monitoring of changes over time.

• External Quality Assessment Schemes (e.g., NEQAS national external quality assesment scheme) help ensure the accuracy and reliability of tests.

• Sensitivity: The ability of a test to correctly identify individuals with a condition.

• Specificity: The ability of a test to correctly identify individuals without a condition.

Post-analytical Variables

Causes of Enzyme Elevations and Protein Alterations

• Extensive cell damage.

• Cell proliferation (e.g., cancer and newborn babies have similar signalling).

• Enzyme induction (e.g., alcoholism). This process can lead to altered drug metabolism and response in individuals.

• Duct obstruction (e.g., amylase and lipase in pancreatitis).

  protein alterations

• Altered protein structures (e.g., glycated hemoglobin in diabetes).

• Loss of organ function (e.g., reduced albumin production in liver disease).

• Protein induction due to cancer (e.g. monoclonal antibodies in myeloma).

• Lack of removal (e.g., creatinine in kidney disease).

Blood Collection Tubes and Their Uses

• Trisodium Citrate (cap colour;Light Blue): Used for coagulation tests (e.g., INR< APTT, D-dimer); citrate acts as a reversible anticoagulant by binding calcium. coagulation is dependant on calcium.

• Gel Tubes (Gold/Yellow): Serum separating tubes used for most biochemistry tests, containing a clot activator, but include no anticoagulant.

• Ethylenediaminetetraacetic acid EDTA (Lavender): Used for hematology procedures like full blood counts; EDTA irreversibly binds calcium to prevent clotting. tube coated with spray-dried K$2$ EDTA, on its inner wall. Ideal for counting leucocytes, platelets and red blood cells, or for flow cytometry as the morphologies of the blood cells are preserved.

• Lithium Heparin (Green): Used for genetics and some biochemistry tests.

• Sodium Fluoride (Grey): Inhibits glycolysis and is used for glucose and lactate measurements; contains EDTA for anticoagulation.

Specimen Selection and Handling

• Plasma: Contains platelets and is used for coagulation studies.

• Serum: Used in biochemistry after coagulation has occurred.

• Urine: Commonly used for kidney-related tests.

• CSF: For neurological disorders and infections.visual examination exihibits normal clear and colourless appearence, bright red-damaged blood vesssel or a recent haemorrage, xanthochromia is a yellow coloration of the CSF and results from altered haemoglobin.

• Proper blood collection order is vital to prevent cross-contamination between tubes.

• Specific cases like cryoglobulinemia require special handling to prevent protein precipitation, as they are insoluble at room temp. paraproteins precipitate in cold conditions, 90% linked with drug users.

• Ammonia samples need to be collected on ice to prevent rapid increases in ammonia levels. mainly liver failure tests

Major Body and Organ System Investigations

Renal Function

Key markers include:

• Urea: A product of amino acid breakdown.

• Creatinine: A waste product from muscle metabolism.
  $eGFR$: calculated from creatinine, age, sex, and ethnicity.

• Albumin: Normally reabsorbed by the kidneys; proteinuria indicates kidney damage.

• Bicarbonate: Marker in the acid production; helps maintain acid-base balance.

• Sodium and Potassium: Controlled in the kidneys; help regulate blood pressure.

Liver Function

Key markers include:

• ALT (Alanine Transaminase): Enzyme prevalent in the liver.

• AST (Aspartate Transaminase): Enzyme found in the liver and other tissues.

• ALP (Alkaline Phosphatase): Enzyme found in the liver and bones.

• GGT (Gamma-Glutamyl Transferase): Enzyme indicating liver damage.

• Bilirubin: Conjugated by the liver for removal.

• Albumin: Synthesized by the liver; low levels indicate liver damage.

• Prothrombin: Coagulation protein.

Tumor Markers

• AFP (Alpha-Fetoprotein): Marker for hepatocellular carcinoma.

• CEA (Carcinoembryonic Antigen): Associated with colorectal, breast, and lung cancers.

• Specific antibodies in multiple myeloma.

• Carbohydrate antigens CA 15-3, CA 19-9, CA 125, and CA 50 for breast, pancreatic, ovarian, and colorectal cancers, respectively.

Bone Profile

• Alkaline Phosphatase (ALP): Can be high with bone turnover.

• Calcium and Phosphate: Essential for bone health.

• Vitamin D: Controls calcium uptake and bone health.

• Parathyroid Hormone (PTH): Regulates bone calcium states. If calcium or phosphate is low, there is elevated bone turnover with alkaline phosphatase.

Other Systems and profiles

• Toxicological: Detects drugs, toxins, and heavy metals.

• Cholesterol and Lipids: Assesses risk of heart disease.

• Nutritional: Assesses vitamin and mineral deficiencies.

• Pituitary: Assesses hormone imbalances.

• Thyroid: Assesses thyroid function.

• Heart: Detects myocardial infarction.

• Acid-Base: Assesses acid-base balance.

• Pancreatic: Assesses pancreatic function. amylase and lipidsis blocked from leaving the pancreas so they travel wherever they want, people with pancreatitis end up with these horrible wounds, seeping sores on their skin the reason why that happens is because the lipase has left the pancreas has travelled around their body and then it reaches an area of blood supply where it slows down, the skin that tends to be where blood is moving quite slowly and then it starts to just sort of digesting the skin, which is all lipids, these sores are due to these pancreatic enzymes.

• Adrenal: Assesses hormones secreted by the adrenal glands.

• Muscular: Assess muscle disease.

• Immune: Assess immune disorders.
  Reference guide is not exhaustive, just a compilation of many important tests.

Renal Function in Detail

• Urea: Product of amino acid breakdown; if creatinine is normal but urea is not, kidney is still in good shape.

• Creatinine: Waste product, comes in the form of creatine powder often. Waste product of the breakdown of muscule.

• Proteinuria: Albumin is not being brought back efficiently enough. Usually indicated chronic kidney diseases.
  *Bicarbonate: Needed to remove the acidic load of acidic metabolism. If you have something acidic, you can give them bicarbonate.

• Kidneys, then, cannot bring this back, as in kidney disease you begin the cycle of acidification quickly.
  *For fluid control, we are reabsorbing the sodium then water follows

Liver Function

Everything that you consume into your intestines gets absorbed and it passes past the liver, we call this the first pass, and this is why most drugs don't work, If you can't take a drug orally and it has to be injected, it's probably because the liver removes it, The liver is excellent at removing alcohol. It is removing anything toxic anything suspicious, It will metabolise away and then make inactive. When you consume alcohol, it's absorbed through your intestines and it passes the liver, The liver will inactivate most of the alcohol and will bind to all of the alcohol. and its measured through the unit system, how long it takes your body to metabolise the alcohol in an hour.