Clinical Chemistry Flashcards

Random Error vs. Systematic Error

• Error Definition: The difference between test and reference method results.

Random Error (RE)

• Definition: Unpredictable variations in repeated measurements under the same conditions.
• Cause: Instrumental fluctuations, operator variability, environmental factors (temperature changes).
• Calculation: Standard deviation (SD) of the points about the regression line ($S_{y/x}$).
  • $S_{y/x}$ represents the average distance of data from the regression line.
  • Higher $S_{y/x}$ implies wider scatter and more random error.
• Effect:
  • Causes scatter around the mean value.
  • Affects precision (reproducibility), not accuracy.
• Detection:
  • Increased standard deviation or coefficient of variation (CV).
  • Detected through replicate testing.

Systematic Error (SE)

• Definition: Consistent, predictable error that skews results in the same direction.
• Influences observations consistently (higher or lower).
• Estimation: Measures of slope and y-intercept provide estimates of systematic error.
• Types:
  • Constant Error: Continual difference between test and comparative method values, regardless of concentration.
  • Proportional Error: Differences between test and comparative method values are proportional to analyte concentration; slope ≠ 1.
• Cause:
  • Calibration errors.
  • Reagent degradation.
  • Instrument bias.

Glucose Oxidase Specificity

• Glucose oxidase is the most specific enzyme for beta-D-glucose.
• It reacts only with β-D-glucose, converting it to gluconic acid.

Spectrophotometer Components

• A spectrophotometer includes:
  • Light source
  • Monochromator (with wavelength selector)
  • Sample holder (cuvette holder)
  • Photodetector
  • Readout device.
• Process: Light from the source is focused and separated into specific wavelengths by the monochromator, passed through the sample in the cuvette. The photodetector measures transmitted light, and the readout device displays absorbance or transmittance.

Chromatography Modes of Separation

1. Adsorption Chromatography (Liquid-Solid Chromatography):
   • Based on competition between the sample and mobile phase for adsorptive sites on the solid stationary phase.
   • Equilibrium between solute molecules adsorbed to the solid surface and desorbed/dissolved in the mobile phase.
2. Partition Chromatography (Liquid-Liquid Chromatography):
   • Separation based on relative solubility in an organic (nonpolar) solvent and an aqueous (polar) solvent.
   • Simple form: extraction in a separatory funnel.
3. Steric Exclusion:
   • Separation based on size and shape using a porous material in the chromatographic column.
   • Different-sized molecules move down the column at different rates when dissolved in the mobile solvent.
4. Ion-Exchange Chromatography:
   • Separation based on magnitude and charge of ionic species.
   • Stationary phase: resin with charged functional groups (polymers of substituted benzene, silicates, or cellulose derivatives).

Methods for Total Protein Determination

• Gravimetric Method:
  • Based on the estimation of the mass percent of an ion in an impure compound by determining the mass of the same ion in a pure compound.
• Kjeldahl Method:
  • Convert organic (and inorganic) nitrogen to ammonium sulfate by digestion at 400–420 °C in a $K<em>2SO</em>4/H<em>2SO</em>4$ mixture with a catalyst.
  • Estimate nitrogen concentration by distilling the ammonium sulfate in the presence of NaOH and titrating the ammonia with standard acid.
• Biuret Method:
  • Colorimetric reaction where a color change from blue to purple/violet indicates the presence of peptide bonds.
  • In an alkaline environment, cupric ($Cu^{+2}$) ions in the biuret reagent bind to nitrogen atoms in peptide bonds, forming a violet-colored coordination complex.
  • Intensity of the developed purple color is directly proportional to the concentration of peptide bonds present.
• Phenol/Lowry Method:
  • Employs Folin and Ciocalteau reagent (lithium salts of phosphotungstic - phosphomolybdic acid) in an alkaline solution.
  • Reduced to a blue color in the presence of:
    • Tyrosine
    • Tryptophan
  • Also known as the Phenol method because phenol is used as the oxidizing agent.
• Turbidimetric Method:
  • Based on measuring the cloudiness (turbidity) or light scattering of a solution when proteins precipitate out.
  • Turbidity is proportional to the protein concentration in the sample.
  • Diluted serum is treated with sulfosalicylic acid or trichloracetic acid, causing protein precipitation.
• Refractive Index Measurement:
  • The refractive index increases as the protein concentration increases.
  • RI measurements can be used to determine protein content.

Diagnostic Sensitivity vs. Specificity

• Diagnostic Sensitivity:
  • Ability of a test to correctly identify those with the disease (true positives).
  • Answers: "If a person has the disease, how often will the test be positive?"
  • Formula: $Sensitivity = \frac{True Positives}{True Positives + False Negatives}$
• Diagnostic Specificity:
  • Ability of a test to correctly identify those without the disease (true negatives).
  • Answers: "If a person does not have the disease, how often will the test be negative?"
  • Formula: $Specificity = \frac{True Negatives}{True Negatives + False Positives}$
• In simple terms:
  • Sensitivity = correctly detecting disease
  • Specificity = correctly ruling out disease

Differentiating Primary from Secondary Hypothyroidism

• Thyroid Stimulating Hormone (TSH) is the best parameter to differentiate.
• Primary Hypothyroidism:
  • Underactive thyroid gland leads to low thyroid hormone levels.
  • Pituitary gland releases high amounts of TSH to stimulate the thyroid.
  • High TSH indicates a primary thyroid issue.
• Secondary Hypothyroidism:
  • Insufficient TSH production by the pituitary gland.
  • Leads to low thyroid hormone levels despite a low or inappropriately normal TSH.
  • Low or normal TSH suggests a problem with the pituitary gland.

Significance of C-Peptide in DM Diagnosis

• C-peptide is a crucial biomarker in the differential diagnosis of DM as it indicates endogenous insulin secretion.
• Helps distinguish between:
  • Autoimmune destruction of beta cells (type 1 DM)
  • Insulin resistance with preserved beta-cell function (type 2 DM).
• Type 1 DM:
  • Autoimmune destruction of beta cells, leading to little or no endogenous insulin production.
  • C-peptide levels are typically low or undetectable.
• Type 2 DM:
  • Associated with insulin resistance and relative insulin deficiency.
  • Patients usually have normal or elevated C-peptide levels, reflecting preserved or increased endogenous insulin production.

Compensation for Metabolic Acidosis

• In primary metabolic acidosis, the amount of acid exceeds the buffering capacity, and there is a decrease in bicarbonate.
• Decrease in pH is due to the decreased ratio of the metabolic to respiratory component in the Henderson-Hasselbalch equation.
• Compensation:
  • Primary Compensation: Hyperventilation (increased rate or depth of breathing) to expel $CO_2$, normalizing the base-to-acid ratio and elevating pH.
  • Secondary Compensation: Kidneys excrete hydrogen ions and reabsorb bicarbonate ions.

Mechanisms of Parathyroid Hormone (PTH) to Increase Plasma Calcium

• PTH increases plasma calcium concentration by three primary mechanisms:

  1. Increases Bone Resorption of Calcium:
     • PTH stimulates osteoclast activity to break down bone matrix, releasing calcium ($Ca^{2+}$) and phosphate ($PO_4^{3-}$) into the bloodstream.
  2. Increases Intestinal Absorption of Calcium:
     • PTH stimulates renal conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D (calcitriol).
     • Calcitriol increases calcium absorption from the intestines.
  3. Increases Removal of Phosphate in the Kidneys:
     • PTH increases calcium reabsorption in the distal convoluted tubules of the kidneys, reducing urinary calcium excretion and conserving calcium in the body.

Negative and Positive Feedback Mechanisms

• Negative Feedback Loop:
  • A stimulus feeds back upstream to decrease its own production.
  • Thyroid Example:
    • Hypothalamus initiates secretion of thyrotropin releasing hormone (TRH).
    • TRH stimulates the anterior pituitary gland to produce thyroid stimulating hormone (TSH).
    • TSH stimulates the thyroid gland to release T3 and T4.
    • T3 and T4 negatively feedback at the hypothalamus and anterior pituitary to decrease TRH and TSH release.
• Positive Feedback Mechanisms:
  • Increase the stimulus received until a distinct endpoint is achieved.
  • Require counter-regulatory mechanisms to prevent them from going out of control.
  • Parturition (Childbirth) Example:
    • Stretch receptors on the cervix feel pressure, stimulating the hypothalamus and posterior pituitary gland to release oxytocin.
    • Oxytocin causes the myometrium of the uterus to increase the rate and strength of contractions.
    • Increased contraction pressure creates greater pressure on the cervix, causing more stimulation of stretch receptors and more oxytocin release.
    • This cycle continues until delivery.
    • The loop ends when the baby is born and its head is no longer exerting pressure on the cervix.

Anterior and Posterior Pituitary Hormones

• Anterior Pituitary Hormones (APH):
  • Thyroid-Stimulating Hormone (TSH)
  • Adrenocorticotropic Hormone (ACTH)
  • Follicle-Stimulating Hormone (FSH)
  • Luteinizing Hormone (LH)
  • Prolactin (PRL)
    *Growth Hormone (GH)
• Posterior Pituitary Hormones (PPH):
  • Oxytocin
  • Antidiuretic Hormone (ADH), also known as Vasopressin (AVP)

Effect of Bubbles on Blood Gas Parameters

• Bubbles in the specimen cause the measured $pO<em>2$ to rise markedly and the $pCO</em>2$ to fall as $CO_2$ diffuses into the bubble.
• pH and bicarbonate remain unchanged.

Differentiating Prehepatic, Hepatic, and Posthepatic Jaundice

• Prehepatic Jaundice:
  • Red blood cells break down, leading to increased unconjugated bilirubin in the blood.
  • Liver can conjugate bilirubin, but the amount is overwhelming.
  • Liver enzymes remain normal.
  • No bilirubin in the urine.
• Hepatic Jaundice:
  • Liver is affected, resulting in a rise in both unconjugated and conjugated bilirubin.
  • AST/ALT levels increase.
  • Bilirubin is present in the urine.
• Posthepatic Jaundice:
  • Blockage in the bile ducts after conjugated bilirubin has been processed.
  • Conjugated bilirubin increases in the blood.
  • Dark urine, pale stools, and increases in alkaline phosphatase and GGT are observed.

Lipoprotein Electrophoresis Results for Turbid Plasma with Creamy Plaque

• Turbid plasma with a creamy layer (creamy supernatant or plaque) indicates Type IIb or Type III hyperlipoproteinemia.

• Creamy Top Layer: Indicates the presence of chylomicrons (large triglyceride-rich lipoproteins).

• Turbid Plasma Beneath: Suggests elevated VLDL or IDL, rich in triglycerides and cholesterol.

• Expected Results:

  • Chylomicrons: Remain at the origin (don't migrate).
  • Increased β-lipoproteins (LDL) and pre-β-lipoproteins (VLDL): Seen as denser bands.

  1. Type IIb Hyperlipoproteinemia:

     • Elevated LDL (β-band) and VLDL (pre-β band).
     • Creamy top (from chylomicrons).
     • Turbid plasma due to VLDL.

  2. Type III (Familial Dysbetalipoproteinemia):

     • Broad β-band (combined remnant particles: IDL, β-VLDL).
     • Turbid plasma with creamy top possible, depending on fasting state.

Basic Renal Processes

1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion

Crystallized Substances Forming Renal Calculi

• Calcium Oxalate: The most prevalent type of kidney stone.
• Calcium Phosphate: Typically forms in alkaline urine and is associated with conditions like renal tubular acidosis and hyperparathyroidism.

OGTT Results for Diagnosing GDM

• One-Step Approach:
  • 75-gram, 2-hour oral glucose tolerance test (OGTT) done between 24 and 28 weeks of pregnancy.
  • Morning test after fasting for at least 8 hours.
  • Blood sugar levels measured at fasting, 1 hour, and 2 hours.
  • GDM is diagnosed if any one of the following values is met or exceeded:
    • Fasting ≥92 mg/dL
    • 1 hour ≥180 mg/dL
    • 2 hours ≥153 mg/dL
• Two-Step Approach:
  • Step 1:
    • 50-gram glucose drink, and blood sugar is checked after one hour.
    • If the result is 140 mg/dL or higher, proceed to Step 2.
  • Step 2:
    • 100-gram, 3-hour oral glucose tolerance test (OGTT), done after fasting for 8 to 14 hours.
    • At least three days of a normal diet and regular activity before this test.
    • Blood sugar is measured at fasting, 1 hour, 2 hours, and 3 hours.
    • GDM is diagnosed if any two of the following values are met or exceeded:
      • Fasting ≥95 mg/dL
      • 1 hour ≥180 mg/dL
      • 2 hours ≥155 mg/dL
      • 3 hours ≥140 mg/dL

Marijuana's Longest Detection Time

• Marijuana has the longest detection time mainly because its active chemical, Tetrahydrocannabinol (THC), is fat-soluble and gets stored in the body's fatty tissues.
• Over time, THC is slowly released back into the bloodstream and metabolized, which can cause it to be detectable for days or even weeks after use, especially in chronic users.
• Key reasons for the long detection time include:
  • Fat solubility- THC binds to fat molecules, so people with higher body fat retain it longer.
  • Frequency and amount of use- Chronic or heavy users accumulate more THC in fat stores, extending detection up to 30 days or more, while occasional users clear it faster (3 days or so).
  • Metabolism- Individuals with slower metabolism eliminate THC more slowly.
  • Type of drug test - Urine and hair tests detect THC metabolites longer (up to 90 days in hair), while blood and saliva tests have shorter windows (hours to a few days).
• In summary, marijuana's long detection window is due to THC's fat storage and slow release, combined with user-specific factors like body fat, usage patterns, and metabolism, as well as the sensitivity of the drug test used.

Specimen of Choice for Lead Screening

• Whole Blood
• Lead accumulates in RBCs, bones, and neural tissues.
• Whole blood, hair, and urine are suitable for demonstrating lead toxicity.
• Greatest sensitivity is obtained by using whole blood, which can detect exposure over time.
• Serum or plasma should not be used because lead is rapidly eliminated from plasma.

Metal Used as Treatment for Wilson’s Disease

• Copper
• However, copper is not directly administered:
  • Copper chelation therapy or copper-reducing medications are used to manage the disease by removing excess copper from the body

Tumor Marker for Herceptin Therapy

• The tumor marker used to determine the usefulness of Herceptin (trastuzumab) therapy is HER2 (human epidermal growth factor receptor 2).
• HER2 is a protein that, when overexpressed or amplified in breast cancer cells, can drive tumor growth.
• Herceptin is a monoclonal antibody that specifically targets and inhibits HER2, making it effective primarily in treating HER2-positive breast cancers.

Creatinine for Assessing Kidney Function

• Creatinine is utilized to assess kidney function because it is a waste product generated at a relatively constant rate from muscle metabolism, specifically from creatine, which is derived from amino acids like methionine, arginine, and lysine.
• Since creatinine is not significantly reabsorbed by the kidneys and is primarily eliminated through glomerular filtration, its concentration in the blood serves as a reliable indicator of renal function.
• Elevated serum creatinine levels may suggest impaired kidney function, as the kidneys are less effective at filtering and excreting this waste product.

Different Creatinine Tests

• Serum Creatinine Test
• Urine Creatinine Test
• Creatinine Clearance
• Estimated Glomerular Filtration Rate Creatinine Clearance
• Creatinine clearance is derived by mathematically relating the serum creatinine concentration to the urine creatinine concentration excreted during a period of time, usually 24 hours. Specimen collection, therefore, must include both a 24-hour urine specimen and a serum creatinine value, ideally collected at the midpoint of the 24-hour urine collection.
• The urine container must be kept refrigerated throughout the duration of both the collection procedure and the subsequent storage period until laboratory analysis can be performed.
• Creatinine clearance is calculated using the following formula:
  • $Cr = \frac{U<em>{cr} \times V</em>{ur}}{P_{cr}} \times \frac{1.73}{A}$
  • Where:
    • Cr = Creatinine clearance
    • $U_{cr}$ = Urine creatinine concentration
    • $V_{ur}$ = Urine volume excreted in 24 hours
    • $P_{cr}$ = Serum creatinine concentration
    • 1.73/A = Normalization factor for body surface area
    • 1.73 = Generally accepted average body surface in square meters
    • A = Actual body surface area of the individual determined from height and weight

Hormones Regulating Serum Calcium

• The three hormones that regulate calcium levels are:

• Parathyroid hormone (PTH):

  • Released by the parathyroid glands in response to a decrease in serum calcium.
  • Acts on the kidneys to increase calcium reabsorption in the ascending loop of Henle, the distal convoluted tubule, and the collecting duct.
  • Acts on the bones to stimulate osteoclasts involved in bone reabsorption and the release of free calcium.
  • The kidney also responds to PTH by increasing secretion of Vitamin D3, which stimulates calcium absorption through the gut.

• 1,25-dihydroxyvitamin D-3 (Vitamin D3):

• Calcitonin:

  • Released by the thyroid parafollicular cells (C-cells) in response to an increase in serum calcium.
  • Acts on the bones to stimulate osteoblasts to deposit calcium in bones.
  • Inhibits renal reabsorption of calcium, increasing urinary calcium excretion.
  • Inhibits calcium absorption in the intestines.

Advantages of Cystatin C for Assessing GFR

1. Less Affected by Muscle Mass and Diet

   • Unlike creatinine, cystatin C levels are not significantly influenced by muscle mass, age, sex, or diet, nor are they generally affected by most drugs, infections, diet, or inflammation.

2. More Sensitive to Early Changes in GFR

   • Cystatin C levels rise earlier than creatinine in mild or early kidney dysfunction, making it a more sensitive marker for detecting subtle decreases in kidney function.

3. Independent of Tubular Secretion

   • Cystatin C is freely filtered by the glomerulus and not secreted by renal tubules, unlike creatinine, which is partly secreted by tubules—this improves the accuracy of GFR estimation.

4. Cystatin C is a more reliable, unbiased, and sensitive GFR biomarker than creatinine, especially for early CKD detection, special populations, and risk stratification.

   • Cystatin C measurements may be performed by particle-enhanced immunoturbidimetric or immunonephelometric methods.

DM Type 1 vs. Type 2

Significance of Measuring Bilirubin Levels in Newborns

• At birth, the enzyme bilirubin UDP-glucuronosyltransferase, which conjugates bilirubin to glucuronic acid, is too immature to complete the process, and increased levels of unconjugated bilirubin and “physiologic” jaundice result.
• A normal baby may have a serum bilirubin level of up to 12 mg/dL, most of which is unconjugated.
• Excessive jaundice can lead to kernicterus and severe brain damage, thus the measurement of total and direct (conjugated) bilirubin has a critically important role in pediatrics.

Significance of Determining Osmolal Gap

• The osmolal gap is the difference between measured and calculated osmolality.
• The osmolal gap indirectly indicates the presence of osmotically active substances other than $Na^+$, urea, or glucose, such as ethanol, methanol, ethylene glycol, isopropanol, lactate, or β-hydroxybutyrate.
• For example: the osmolal gap may be used in cases of ethylene glycol poisoning since ethylene glycol isn’t routinely measured in the blood.
• When present in the blood, the osmolal gap is elevated.
• The normal range of the osmolal gap is 5-10 mOsm/kg, but in ethylene glycol poisoning it is >10 mOsm/kg.

Effects of Prolonged Tourniquet Use or Excessive Fist Clenching on Serum Electrolytes

• Potassium ($K^+$):
  • Muscle activity and pressure from a prolonged tourniquet can lead to potassium shifting from cells into the bloodstream, causing pseudohyperkalemia, resulting in falsely elevated potassium levels.
• Total Protein and Calcium:
  • Hemoconcentration elevates the concentration of proteins and calcium in the blood, which may not reflect the true concentration of these substances in the body.
• Sodium ($Na^+$) and Chloride ($Cl^-$):
  • These electrolytes may also show slight increases, although less pronounced than potassium, due to hemoconcentration.

Chloride Shift

• Electroneutrality is maintained by Chloride ($Cl^−$) through the chloride shift.
• In tissues:
  • $CO_2$ from metabolism diffuses into RBCs.
  • Carbonic anhydrase converts $CO<em>2 + H</em>2O → H<em>2CO</em>3 → H^+ + HCO_3^−$.
  • $HCO_3^−$ exits the RBC, and $Cl^−$ enters to balance charge.
• In lungs:
  • Reverse process occurs for $CO_2$ elimination
• This mechanism:
  • Maintains acid-base balance
  • Ensures electrical neutrality across RBC membranes
  • Enhances $CO_2$ transport from tissues to lungs

Hypogonadotropic vs. Hypergonadotropic Hypogonadism

• Hypogonadotropic hypogonadism
  • Also known as gonadotropin (Follicle Stimulating Hormone and Luteinizing Hormone) deficiency resulting in decreased sex steroid production is a common cause of secondary amenorrhea.
  • Its physiologic and pathologic cause includes weight loss as associated with anorexia nervosa or various disease processes, intense physical exercise and pituitary tumors that disrupts the secretion of FSH or LH.
• Hypergonadotropic hypogonadism
  • Characterized by ovarian failure resulting in elevation of FSH concentration, with or without LH elevations.

Importance of SPE with CSF Electrophoresis

1. To Identify Systemic Protein Abnormalities:

   • SPE helps to identify any unusual protein patterns in the serum (blood).
   • Since CSF is derived from blood plasma, systemic protein abnormalities can also affect the CSF protein profile.
   • Comparing the CSF electrophoresis pattern with the SPE pattern allows clinicians to determine if a particular protein abnormality in the CSF originates from the blood or if it is being produced within the central nervous system (intrathecal production).

2. To Detect Blood-Brain Barrier Integrity:

   • The blood-brain barrier (BBB) normally restricts the passage of large proteins from the blood into the CSF.
   • An intact BBB should result in a CSF protein profile that is distinct from serum, with lower total protein and different relative concentrations of specific proteins.
   • If the BBB is compromised due to various neurological conditions (e.g., meningitis, tumors, inflammation), serum proteins can leak into the CSF.
   • Comparing CSF electrophoresis with SPE helps assess the integrity of the BBB by identifying increased levels of serum proteins (like albumin) in the CSF.

3. To Differentiate Intrathecal Synthesis from Serum Transudation:

   • Certain neurological conditions, most notably multiple sclerosis (MS) and some central nervous system infections, can lead to the intrathecal synthesis of immunoglobulins (antibodies) within the CSF.
   • On CSF electrophoresis, this intrathecal production often manifests as oligoclonal bands – distinct bands in the gamma globulin region that are not present in the corresponding SPE.
   • The absence of these bands in the serum confirms that their presence in the CSF is due to local production within the CNS and not due to leakage from the blood.

Blood Collection Tubes

• Blood is collected in specific tubes because each tube contains anticoagulants specific to different tests.

  • Yellow (Sodium Polyanethol Sulfonate) - for culture
  • Blue / Light blue (3.2% Sodium Citrate) - Coagulation Tests
  • Red (No additive) - Immunosero Tests and Chemistry
  • Green (Heparin) - Plasma Chem and ABG
  • Lavender (EDTA) - Hematology tests
    *Black (3.8% Sodium Citrate) - ESR

• It's important to observe the proper order of draw to prevent the carryover of anticoagulants.

• Example: For calcium and CBC, the red top tube should be filled before the purple because EDTA chelates calcium, if purple is drawn first, it might cause a false decrease in calcium.

Urinary pH and Specific Gravity in Kidney Disease

• We measure urinary pH to assess how well the kidneys regulate acid–base balance, and specific gravity to evaluate their ability to concentrate or dilute urine.
• Abnormal values in either may indicate tubular dysfunction or kidney damage, making them important markers in suspected kidney disease.

Role and Importance of Albumin

• Maintains Colloidal Osmotic Pressure (Oncotic Pressure):

  • Albumin is the most abundant plasma protein (~60% of total protein).
  • It exerts osmotic pressure that helps keep fluid within the vascular compartment, preventing edema.

• Transport Function:

  • Albumin also serves as a transport protein, binding and carrying a wide variety of substances including free fatty acids, bilirubin, hormones, drugs, and metal ions such as calcium.

• Buffering Capacity:

  • it contributes to the buffering capacity of blood, helping to maintain acid-base balance by acting as a buffer
    *Importance of Measuring Albumin Levels:
  • Marker of Nutritional Status: Low albumin may indicate malnutrition or chronic illness.
  • Indicator of Liver Function:Albumin is synthesized in the liver and hypoalbuminemia may signal liver dysfunction (e.g., cirrhosis, hepatitis).
  • Assessment of Renal Function:Albuminuria suggests glomerular damage (e.g., in nephrotic syndrome).
  • Disease Monitoring and Prognosis: Low serum albumin is associated with poor prognosis in critically ill patients and is useful in monitoring chronic diseases, inflammation, or protein-losing enteropathies.

• Normal Reference Range (per Bishop): 3.5–5.0 g/dL in serum

Enzymes as Biomarkers

• Enzymes are globular proteins acting a biochemical catalyst making it possible for reactions to take place under normal conditions. Normally, enzymes are produced at low levels and found within the cells. However, during cellular injury they are released in great amount in the serum.
• Increased in enzymes indicates a damage in tissues. Their activity in biological fluids like blood can indicate various diseases or conditions, providing valuable insights into organ function and disease progression.

Importance of Fasting for Lab Tests

• Recent food consumption falsely increase glucose and lipid levels, therefore providing inaccurate results.
• Fasting gives us a true picture of a patient's metabolic health and is essential in diagnosing, managing, and monitoring of conditions like that of diabetes.
• It is also important to not overfast as this can falsely decrease glucose and lipid results.
• Extended fasting may lead to hypoglycemia, dehydration, and electrolyte imbalances, which can adversely affect test outcomes and patient health.
• Thus, it is important for Medtechs to clearly instruct patients and make them understand the need for fasting before getting their blood drawn for the said lab tests.
• Side notes:
  • FBG should be obtained in the morning after an approximately 8- to 12-hour fast.
  • Lipid profile minimum of 12 hours. (max is 14?)
• Other tests which require fasting:
  • OGTT - need baseline glucose levels
    *Gastrin - need baseline levels; eating increases gastrin release
  • Aldosterone/renin -Fasting helps minimize the impact of electrolyte shifts caused by recent meals; evaluate hypertension causes
  • Insulin - fluctuate during meals

Causes of Pseudohyponatremia

• Pseudohyponatremia can occur when $Na^+$ is measured using indirect ion-selective electrodes (ISEs) in a patient who is hyperproteinemic or hyperlipidemic.

• An indirect ISE dilutes the sample prior to analysis, and as a result of serum/ plasma water displacement, the ion levels are falsely decreased.

• Pseudohyponatremia may also be seen with in vitro hemolysis, considered the most common cause for a false decrease.

• When red blood cells (RBCs) lyse, $Na^+$, $K^+$, and water are released, and since $Na^+$ concentration is lower in RBCs, this results in a false decrease.

• Hyponatremia is defined as low serum/plasma $Na^+$ levels, usually less than 135 mmol/L, and levels below 120 mmol/L are clinically significant.

• Hyponatremia is one of the most common electrolyte disorders in hospitalized and nonhospitalized patients and can be assessed either by the cause of the decrease or with the osmolality level.

LDH Levels in Cancer

• In cancer, LDH is often used as a biomarker to help monitor the disease. Elevated LDH levels can be associated with tumor progression, metastasis, and poor prognosis.

• EXPLANATION: LDH (lactate dehydrogenase) is an enzyme that helps cells produce energy. Most of the time, cells use oxygen to make energy, but cancer cells often switch to a different method that doesn't need oxygen — called anaerobic glycolysis. This method creates a lot of lactate, and LDH is the enzyme that makes that happen. So, when someone has cancer, especially fast-growing or aggressive cancer, their body may have more LDH than usual because:

  • Cancer cells are making a lot of energy without oxygen.

  • More lactate is being made, and LDH helps with that.

  • Some cancer cells or damaged tissues release LDH into the blood.

Beer's Law

• Beer law states that the concentration of a substance is directly proportional to the amount of light absorbed or inversely proportional to the logarithm of the transmitted light.

• Beer's Law is used in spectrophotometric assays to measure the concentration of various substances in blood, urine, and other body fluids.

• Example Applications:

  1. Glucose measurement:

     • Enzymatic methods (like glucose oxidase) produce a colored compound.

     • The intensity of the color (measured by absorbance) is proportional to glucose concentration.

  2. Liver and kidney function tests:

     • Enzymatic reactions generate chromophores whose absorbance can be quantified.

  3. Drug concentration monitoring:

     • Therapeutic drug levels in plasma can be estimated by comparing absorbance to standard curves.

Quality Control Materials

• The use of quality control (QC) materials in clinical chemistry testing is essential to ensure the accuracy, precision, and reliability of laboratory results.

• According to Bishop's Clinical Chemistry (9th edition), QC materials help verify that analytical methods are functioning properly and that test results are consistent over time.

• They serve as a benchmark to detect errors or shifts in assay performance before patient results are reported, thereby safeguarding patient safety and ensuring high-quality laboratory service (Bishop, 2019, p. 123).

Serum and Plasma

• Serum: Liquid portion after coagulation (no fibrinogen)

• Plasma: Liquid portion with clotting factors (contains fibrinogen)

Calibration

• Calibration is the comparison of an instrument measurement or reading to a known physical constant (standard or calibrator). It is done to measure accuracy of the results.

AST and ALT

• AST is often measured alongside ALT