6.1

Summary

text

DIABETES MELLITUS: GENERAL OVERVIEW AND EPIDEMIOLOGY

CLASSIFICATION AND ETIOLOGY

• Type 1 DM was formerly called juvenile-onset or insulin-dependent diabetes, but these terms should no longer be used.
• Type 2 DM was formerly called adult-onset or non-insulin-dependent diabetes, but these terms should no longer be used.
• MODY (Maturity-Onset Diabetes of the Young) should be suspected in a young patient (e.g., age 24) who does not respond to metformin but responds to sulfonylureas.
• Chronic glucocorticoid use is a known external cause that can trigger or exacerbate diabetes.

TYPE 1 DIABETES MELLITUS: AUTOANTIBODIES AND GENETICS

• Autoimmune destruction of beta cells in Type 1 DM leads to an absolute deficiency in insulin production.
• Islet cell cytoplasmic antibodies (ICA) are among the antibodies found in patients with Type 1 DM.
• GAD65 (Glutamic acid decarboxylase) has the highest sensitivity (91%) as a single screening marker for Type 1 DM and is more common in adults.
• Insulin autoantibodies (IAA) are more commonly found in young children with Type 1 DM.
• IA-2 (Insulinoma-associated protein 2) and ZnT8A (Zinc Transporter 8) are found on the surface membrane of pancreatic islet beta cell secretory granules.
• HLA-DR and HLA-DQ genes on chromosome 6 are the primary genetic markers associated with Type 1 DM susceptibility.
• C-peptide and endogenous insulin levels are very low or undetectable in patients with Type 1 DM.
• Diabetic Ketoacidosis (DKA) is the clinical consequence of untreated or absolute insulin deficiency in Type 1 DM.

TYPE 2 DIABETES MELLITUS: RISK FACTORS AND SCREENING

• Type 2 DM screening for Asian Americans should begin at a BMI of ≥23 kg/m² (lower than the standard ≥25 kg/m²).
• Acanthosis nigricans is a clinical sign of insulin resistance commonly seen in Type 2 DM.
• Adult screening for DM should be performed on all adults ≥45 years old, or overweight adults with ≥1 risk factor, every 3 years.
• Pediatric screening for DM should start at age ≥10 or onset of puberty for overweight children with additional risk factors (family history, race, SGA birth weight).
• Dyslipidemia risk factors for Type 2 DM include an HDL ≤35 mg/dL and/or Triglycerides ≥250 mg/dL.
• C-peptide levels are measurable in Type 2 DM, distinguishing it from the absolute deficiency in Type 1.
• Hyperglycemia in Type 2 DM is toxic to beta cell function, leading to a progressive failure of insulin production over time.

DIAGNOSTIC CRITERIA (ADA/WHO)

• Diagnosis of DM generally requires two abnormal results from the same or different tests, unless clinical symptoms of hyperglycemia are present.
• Impaired Fasting Glucose (IFG) primarily reflects liver insulin resistance (excessive glucose production).
• Impaired Glucose Tolerance (IGT) primarily reflects muscle insulin resistance and early pancreatic beta-cell failure post-meal.
• Oral Glucose Tolerance Test (OGTT) preparation requires a minimum of 150g of carbohydrates per day for 3 days prior and an 8–14 hour fast.
• Gestational Diabetes (GDM) screening is performed at 24–28 weeks of gestation for average-risk women.
• Cystic Fibrosis–Related Diabetes annual screening starts at age 10 using OGTT; HbA1c is NOT recommended for these patients.

GLUCOSE MEASUREMENT AND LABORATORY METHODS

• Hexokinase is the gold standard/reference method for glucose measurement because it has the least interference.
• Gray-top tubes contain Sodium Fluoride (anti-glycolytic) and Potassium Oxalate (anticoagulant) and are the traditional preferred specimen for glucose.
• Glycolysis will lower glucose levels in unseparated samples; they must be tested within 30 minutes or kept on ice.
• Vitamin C (Ascorbic acid) can cause falsely high readings in glucose monitors using glucose oxidase or dehydrogenase enzymes due to electrochemical interference.
• Total Allowable Error for glucose analytic performance should be ≤ 6.9%.
• Fasting requirement for glucose is an 8–14 hour fast; fasting beyond 14 hours is discouraged as gluconeogenesis may falsely increase glucose.
• Specimen types for glucose include plasma, serum, whole blood, CSF, and pleural fluid; urine and interstitial fluid are not used for primary diagnosis.
• CSF glucose should ideally be measured 1 hour prior to a lumbar tap for accurate comparison with plasma levels.

MEASURES OF GLYCOSE CONTROL AND ALTERNATIVE MARKERS

• HbA1c (Glycosylated Hemoglobin) reflects the "weighted average" blood glucose over 2–4 months; 50% of the value is determined by the previous month's levels.
• Amadori rearrangement is the chemical process that forms the stable ketoamine measured in HbA1c assays.
• Falsely low HbA1c can be caused by conditions that shorten RBC lifespan, such as hemolysis, blood loss, pregnancy, or erythropoietin therapy.
• Iron deficiency anemia can cause a falsely high HbA1c.
• Fructosamine reflects glycemic control over the preceding 2–3 weeks and is useful when HbA1c is unreliable (e.g., hemoglobinopathies).
• Glycated albumin is better standardized than fructosamine and is not affected by bilirubin, though it is affected by low serum albumin (<3.0 g/dL).
• 1,5-Anhydroglucitol (1,5-AG) reflects short-term (1–2 weeks) glycemic control and specifically detects postprandial glucose excursions/spikes.
• Estimated Average Glucose (eAG) is the standardized calculation used to report HbA1c results in units (mg/dL) comparable to daily monitoring.
• Glucose Management Indicator (GMI) is a newer metric derived from Continuous Glucose Monitoring (CGM) meant to correlate with HbA1c.

KETONE TESTING AND DIABETIC KETOACIDOSIS (DKA)

• Ketone bodies include $\beta$-hydroxybutyric acid, acetoacetic acid, and acetone.
• $\beta$-hydroxybutyrate is the preferred ketone for diagnosis and monitoring of DKA as it more accurately reflects the redox state.
• Sodium Nitroprusside (traditional dipstick) only detects acetoacetic acid and acetone; it does NOT detect $\beta$-hydroxybutyric acid.
• Nitroprusside methods may show a "false negative" or underestimate the severity of early DKA because $\beta$-hydroxybutyrate is the predominant ketone during initial stages.
• Nitroprusside "False Positives" can be caused by sulfhydryl-containing drugs like captopril.
• DKA biochemical criteria include Arterial pH <7.3, Bicarbonate <17 mmol/L, Plasma glucose >250 mg/dL, and $\beta$-hydroxybutyrate >2.0 mmol/L.
• Anion Gap calculation and serial $\beta$-hydroxybutyric acid measurements are used to monitor recovery from DKA.

DIFFERENTIATING ENTITIES AND EXAM TRAPS

1. Type 1 vs. Type 2 DM: Type 1 features absolute insulin deficiency (low C-peptide) and positive autoantibodies; Type 2 features insulin resistance (measurable C-peptide) and clinical signs like acanthosis nigricans.
2. IFG vs. IGT: IFG (Fasting 100-125) relates to liver resistance; IGT (2-hr post-load 140-199) relates to muscle resistance/pancreatic failure.
3. MODY vs. Type 2 DM: MODY is monogenic (single gene), occurs <25 years, and responds well to sulfonylureas; Type 2 is polygenic/familial and often metformin-resistant.
4. HbA1c vs. Fructosamine: Use HbA1c for long-term (3 months) monitoring; use Fructosamine for short-term (2-3 weeks) or if RBC lifespan is altered.
5. 1,5-Anhydroglucitol vs. HbA1c: 1,5-AG is the best marker for identifying postprandial spikes/excursions that HbA1c might miss.
6. Hexokinase vs. Glucose Oxidase: Hexokinase is the most accurate (reference); Glucose Oxidase is affordable but prone to interference by Vitamin C/Uric acid.
7. Nitroprusside vs. enzymatic $\beta$-hydroxybutyrate: Nitroprusside misses the most important ketone in DKA ($\beta$-hydroxybutyrate).
8. Standard OGTT vs. Cystic Fibrosis Screening: Cystic Fibrosis requires OGTT starting at age 10; HbA1c is expressly not recommended for CF diagnosis.
9. Sodium Fluoride vs. Potassium Oxalate: Sodium fluoride inhibits glycolysis (preserves glucose); Potassium oxalate prevents clotting (anticoagulant).
10. Diagnosis vs. Monitoring: HbA1c and FPG are for both; Home blood glucose monitors and Point-of-Care HbA1c are for monitoring only (not diagnosis, unless FDA/NGSP level I lab approved).
11. Falsely Low vs. High A1c: Hemolysis/Bleeding = low (fewer old RBCs); Iron deficiency = high (older RBCs persist).
12. Childhood DM: If obese/signs of resistance, suspect Type 2; if thin/DKA/antibodies, suspect Type 1.
13. Glucose Oxidase Interference: High Vitamin C leads to falsely high glucose in some monitors but can interfere with the chemistry causing false readings.
14. Over-fasting Effect: Fasting >14 hours triggers gluconeogenesis, potentially leading to a falsely elevated sugar level.
15. GDM Screening: One-step uses a 75g-OGTT; Two-step uses a 50g-screen followed by a 100g-OGTT (NIH Consensus).
16. HbA1c "Weighted Average": The most recent month contributes 50% to the total A1c value, making recent spikes influential.
17. GAD65 vs. IAA: GAD65 is the best single marker and adult-linked; IAA is the pediatric-linked marker for Type 1 DM.
18. Red Top vs. Gray Top: Gray top is gold standard for transport; red top is used in practice if serum is separated immediately to stop glycolysis.
19. Ketone Ratio in DKA: The $\beta$-hydroxybutyrate to acetoacetate ratio greatly increases during DKA due to the altered redox state (NADH).
20. Water vs. Coffee during Fasting: Water is allowed for fasting glucose tests; black coffee and smoking are strictly prohibited.

QA

6.2

Summary

text | FEATURE | CEREBROSPINAL FLUID (CSF) | SYNOVIAL FLUID (SF) | SEROUS FLUIDS (Pleural/Peritoneal/Pericardial) | | :--- | :--- | :--- | :--- | | Normal Appearance | Crystal clear; colorless (like water) | Colorless to pale yellow; transparent | Clear; pale yellow to straw-colored | | Normal Volume | 90-150 mL (Adult total); 500 mL produced/day | < 4.0 mL in large joints (e.g., knee) | Minimal; produced & reabsorbed continuously | | Cell Count | 0-5 cells/µL (Adults); 0-30 cells/µL (Neonates) | Monocytes/Macrophages (65%); Neutrophils (<20%) | Mesothelial cells common; variable WBCs | | Glucose Level | 50-80 mg/dL (~60% of plasma glucose) | Similar to plasma; <10 mg/dL difference | Depends on Transudate vs Exudate | | Total Protein | 15-45 mg/dL (Increases with age) | 1.0 - 3.0 g/dL | Low in transudates; High in exudates | | Major Components | Ultrafiltrate/secretion of choroid plexuses | Ultrafiltrate of plasma + Hyaluronic acid | Plasma filtrate from parietal capillaries |

CEREBROSPINAL FLUID (CSF)

Production and Function

• CSF Production in adults occurs at a rate of 0.3 to 0.4 mL/min, totaling approximately 500 mL per day.
• Total CSF Volume in adults ranges from 90 to 150 mL, with 25 mL in the ventricles and the remainder in the subarachnoid space.
• CSF Turnover is rapid, with the total volume being replaced every 5 to 7 hours.
• CSF Origin is 70% derived through ultrafiltration and secretion of the choroid plexuses.
• CSF Functions include physical cushioning (protection), buffering pressure changes, waste removal (transport), and maintaining CNS ionic balance (homeostasis).

Components and Equilibration

• CSF Electrolytes (H⁺, K⁺, Ca²⁺, Mg²⁺, Bicarb) are tightly regulated by specific transport systems rather than simple diffusion.
• CSF Glucose and Urea diffuse freely but require a lag time of 2 hours or longer to equilibrate with plasma.
• Simultaneous Glucose Determination requires that serum glucose be obtained 2 to 4 hours before the lumbar puncture for accurate comparison.
• CSF Proteins cross the blood-brain barrier (BBB) via passive diffusion at a rate inversely proportional to their molecular weight.

Extraction and Opening Pressure (OP)

• Lumbar Puncture Sites include the Lumbar, Cisternal, Lateral Cervical, or via Cannulas/Shunts.
• Normal Opening Pressure in adults is 90-180 mm H₂O; it may be 10 mm higher if the patient is sitting up.
• Infant Opening Pressure ranges from 10-100 mm H₂O.
• Intracranial Hypertension is indicated by a pathologic CSF pressure greater than 250 mm H₂O.
• CSF Removal Precautions dictate that if the opening pressure is >200 mm H₂O in a relaxed patient, no more than 2.0 mL of fluid should be withdrawn.
• Common Causes of Increased CSF Pressure include CHF, Meningitis, Mass lesions, and Cerebral edema.*
• Common Causes of Decreased CSF Pressure include CSF leakage, Herniation, and Spinal subarachnoid block.*
• Herniation Sign: A significant pressure drop after removing only 1-2 mL of CSF suggests a spinal block or impending herniation.

Collection and Handling

• CSF Volume Removal: Up to 20 mL may be removed normally if the opening pressure is within normal limits.
• CSF Collection Tubes: Glass tubes must be avoided because cell adhesion affects counts and differential.
• CSF Tube 1 is used for Chemistry and Immunology; it is never used for Microbiology due to contaminant risk.
• CSF Tube 2 is designated for Microbiologic examination.
• CSF Tube 3 is used for Cytology/Microscopic examination (especially for suspected malignancy).
• CSF Specimen Transport: Specimens must reach the lab within one hour; refrigeration is contraindicated for cultures (fastidious organisms) and flow cytometry.

Gross and Microscopic Examination

• CSF Turbidity or cloudiness occurs when leukocyte counts exceed 200 cells/µL or RBC counts exceed 6000/µL.
• CSF Clot Formation is seen in traumatic taps, spinal block (Froin’s Syndrome), or suppurative/TB meningitis; it is NOT seen in subarachnoid hemorrhage.
• Viscous CSF may indicate metastatic mucin-producing adenocarcinoma or Cryptococcal meningitis (capsular polysaccharide).
• Xanthochromia is a pale pink, orange, or yellow supernatant in centrifuged CSF, indicating old hemorrhage or bilirubin.
• Oxyhemoglobin Xanthochromia (pink-orange) is detected 2-4 hours after subarachnoid hemorrhage, while Bilirubin (yellow) takes 12 hours to develop.
• Traumatic Tap vs SAH: Traumatic taps clear between tubes 1 and 3; SAH shows uniform blood and presence of erythrophages/hemosiderin-laden macrophages.
• Total Cell Count: Ideally, no RBCs are present; adult WBC reference is 0-5 cells/µL.
• Bacterial Meningitis Predictor: A total PMN count >1180/µL or WBC >2000/µL has a 99% predictive value for bacterial meningitis.
• CSF Plasma Cells are never normal; they suggest inflammatory/infectious conditions, Multiple Myeloma, or malignant brain tumors.
• Eosinophilic Meningitis is characterized by >10% eosinophils; the most common cause worldwide is parasitic invasion.
• Erythrophages appear 12–48 hours after hemorrhage; Siderophages (hemosiderin-laden) appear after 48 hours and persist for weeks.
• CSF Malignancy: Acute Lymphoblastic Leukemia (ALL) is the most frequent cancer found in CSF, particularly in children.

Chemical Analysis and Enzymes

• CSF Total Protein is the most common abnormality found; increases indicate BBB breakdown or CNS disease.
• Myelin Basic Protein (MBP) is released during demyelination and is a marker for Multiple Sclerosis.
• ꞵ₂-Macroglobulin levels >1.8 mg/L suggest leptomeningeal leukemia or lymphoma.
• AD Diagnosis Markers: Increased microtubule-associated τ (tau) protein and decreased β-amyloid protein 42 increase Alzheimer’s diagnosis accuracy.
• Hypoglycorrhacia (low CSF glucose <40 mg/dL) indicates bacterial, tuberculous, or fungal meningitis.
• CSF Lactate >35 mg/dL indicates CNS anaerobic metabolism (hypoxia) and helps differentiate bacterial from viral meningitis.
• Adenosine Deaminase (ADA) is an enzyme used primarily to diagnose Tuberculous Meningitis.
• CK-BB levels >40 U/L in CSF correlate with poor outcomes in head trauma or subarachnoid hemorrhage.
• CSF Ammonia levels are elevated in proportion to the degree of hepatic encephalopathy.

Microbiological Findings

• Viral Meningitis shows early neutrophilia but soon shifts to a predominance of lymphocytes; RT-PCR is the gold standard.
• Fungal Meningitis (Cryptococcus): India ink or nigrosin stains show capsular halos; sensitivity increases with multiple taps.
• Tuberculous Meningitis Hallmark: Elevated protein and lymphocytic predominance in an abnormal CSF specimen.

SYNOVIAL FLUID (SF)

Classification and Collection

• Synovial Fluid Identification is essential to distinguish infectious (septic) from non-infectious arthritis.
• SF Classification includes Group 1 (Non-inflammatory), Group 2 (Inflammatory), Group 3 (Septic), and Group 4 (Hemorrhagic).*
• Arthrocentesis Syringes must be plastic and potentially heparinized (25 U/mL) to avoid birefringent particulate contamination.
• Contraindicated SF Anticoagulants: Oxalate, lithium heparin, and powdered EDTA are avoided because they form crystals that mimic pathology.*
• Normal SF Clotting: Normal synovial fluid does NOT clot because fibrinogen is absent.

Gross and Microscopic Examination

• Normal SF Clarity: Newsprint should be easily read through the tube (transparent).
• Rice Bodies: Small white inclusions in synovial fluid, often associated with RA.
• SF Neutrophils exceed 50% in gout, pseudogout, and RA; they exceed 75% in acute bacterial (septic) arthritis.
• Ragocytes are neutrophils with 2-10 intracytoplasmic inclusions; they may indicate a poor outcome in Rheumatoid Arthritis.
• Monocytes/Macrophages are the most common cells (65%) in normal synovial fluid.
• Pathognomonic Finding: Intracellular crystals in neutrophils or macrophages are diagnostic for crystal-induced arthritis.
• Monosodium urate (MSU) crystals are seen in gout; Calcium pyrophosphate (CPPD) is seen in pseudogout.
• Reiter’s Cells are macrophages that have ingested neutrophils.

SEROUS FLUIDS (Pleural, Peritoneal, Pericardial)

Transudates vs Exudates

• Serous Effusion is fluid accumulation caused by an imbalance between production and reabsorption.
• Transudates are usually bilateral, clear, do not clot, and result from systemic pressure imbalances (e.g., CHF).*
• Exudates are usually unilateral, turbid/bloody, and result from localized inflammatory/malignant processes that increase vascular permeability.*
• Pleural Fluid Hematocrit >50% of the blood hematocrit is diagnostic evidence for hemothorax.
• Feculent Odor in serous fluid suggests anaerobic infection.

Chylous vs Pseudochylous

• Chylous Effusions are caused by thoracic duct leakage (lymphoma/trauma) and contain chylomicrons.
• Congenital Chylothorax is the most common form of pleural effusion in newborns.
• Pseudochylous Effusions have a "gold paint" appearance and result from breakdown of lipids in chronic conditions (TB, RA).

Cytology

• Mesothelial Cells are common in inflammatory serous fluids; they can be large and clustered, sometimes mimicking malignancy.
• Malignant Serous Cells are characterized by high N:C ratios, pleomorphism, and dark-staining nuclei.
• Serous Mucin: Presence of mucin in pleural fluid suggests a metastatic source like the GI tract or ovaries.

DIFFERENTIAL DIAGNOSIS AND EXAM TRAPS

QA

OVERVIEW AND COMPARISON

CEREBROSPINAL FLUID (CSF): PRODUCTION AND FUNCTION

CSF: COMPONENTS AND EQUILIBRATION

CSF: EXTRACTION AND OPENING PRESSURE (OP)

CSF: COLLECTION AND HANDLING

CSF: GROSS AND MICROSCOPIC EXAMINATION

CSF: CHEMICAL ANALYSIS AND ENZYMES

CSF: MICROBIOLOGICAL FINDINGS

SYNOVIAL FLUID (SF): CLASSIFICATION AND COLLECTION

SF: GROSS AND MICROSCOPIC EXAMINATION

SEROUS FLUIDS: TRANSUDATES VS EXUDATES

SEROUS FLUIDS: CHYLOUS VS PSEUDOCHYLOUS

DIFFERENTIAL DIAGNOSIS AND EXAM TRAPS

6.3

Summary

text

DIAGNOSTIC TESTING & PRINCIPLES

• TSH Assay: In thyroid function testing, the most sensitive screening test; can detect subclinical abnormalities before T3/T4 change.
• Equilibrium Dialysis: In thyroid health, the gold standard method for directly measuring free T3 and T4 levels.
• Resin T3 Uptake (RT3U): In laboratory diagnostics, an indirect measure of unsaturated binding sites on TBG; increased uptake suggests decreased TBG sites (as seen in hyperthyroidism).
• TRH Stimulation Test: Used in difficult cases to differentiate secondary from tertiary hypothyroidism; tertiary shows an increased TSH response after TRH challenge.
• Radioactive Iodine Uptake (RAIU): Used to differentiate causes of hyperthyroidism; not useful for hypothyroidism.
• Thyroid Antibodies (IgG): In autoimmune testing, Antimicrosomal (Anti-TPO) antibodies are the main hallmark of Hashimoto’s disease.
• Thyroglobulin Antibodies: In clinical oncology, used primarily to monitor patients with thyroid cancer.
• Reverse T3 (rT3): In fetal medicine, measuring rT3 in amniotic fluid is used to diagnose fetal hypothyroidism.
• Thyroid Hormone Half-Life: Bound T4 has a half-life of 7 days, whereas bound T3 has a half-life of only 1 day.
• T3 Suppression Test: In hyperthyroidism, used to evaluate response to drug therapy; normal patients show a 50% suppression of RAIU after T3 administration.
• Hormone Excretion: In metabolism, thyroid hormones are conjugated in the liver; T4 with Glucuronic acid and T3 with Sulfates.
• Estrogen Influence: In liver physiology, estrogen increases the synthesis of TBG, which falsely elevates total T4/T3 despite normal free (active) hormone levels.
• T3 Discriminant Value: In hyperthyroidism, total T3 has a high discriminant value for diagnosis because it reflects both thyroid secretion and T4 to T3 conversion.

DIFFERENTIAL DIAGNOSIS AND EXAM TRAPS

1. T3 vs. T4 Activity: T3 is the most active (about 10-fold more active than T4), whereas T4 is the most abundant and serves as a pro-hormone.
2. TBG vs. TBPA Binding: TBG binds both T3 and T4, but TBPA (Transthyretin) binds T4 ONLY.
3. Primary vs. Secondary Hypothyroidism: In Primary, TSH is increased; in Secondary, TSH is decreased.
4. Secondary vs. Tertiary Hypothyroidism: In the TRH Stimulation test, Secondary (Pituitary problem) shows decreased TSH after challenge, while Tertiary (Hypothalamus problem) shows increased TSH.
5. rT3 vs. T3 Structure: T3 results from iodine removal from the Alpha portion of T4; rT3 results from iodine removal from the Beta portion.
6. rT3 in Illness: rT3 increases in Euthyroid Sick Syndrome/severe non-thyroid illness to conserve body energy, distinguishing it from true hypothyroidism.
7. Graves vs. Hashimoto Antibodies: Graves is primarily Anti-TSH Receptor (TSI); Hashimoto is primarily Anti-TPO (Microsomal).
8. Pregnancy vs. Hyperthyroidism: Pregnancy increases TBG/Total T4 but keeps Free T4 and TSH within narrow limits (or TSH may slightly fall in early pregnancy due to hCG).
9. Resin T3 Uptake Interpretation: High RT3U = Hyperthyroidism (fewer open TBG sites); Low RT3U = Hypothyroidism (more open TBG sites).
10. Calcitonin vs. PTH: Calcitonin (Thyroid) lowers blood Calcium; PTH (Parathyroid) raises blood Calcium.
11. Total vs. Free Hormone Tests: Total T4/T3 are affected by binding protein levels (e.g., liver disease, pregnancy); Free T4/T3 are the true indicators of metabolic status.
12. Primary vs. Secondary Hyperthyroidism: Primary (Graves) has ↑ T4 and ↓ TSH; Secondary (Pituitary tumor) has ↑ T4 and ↑ TSH.
13. Iodide vs. Iodine: Iodide (I-) is the form taken up from plasma; Iodine (I2) is the active form used for organification after oxidation by peroxidase.
14. Hypothyroidism vs. Myxedema Coma: Hypothyroidism is the general condition; Myxedema Coma is the severe medical emergency characterized by hypothermia and progressive stupor.
15. Hormone Excretion Conjugates: T4 is associated with Glucuronic acid; T3 is associated with Sulfates.
16. Subclinical vs. Clinical: "Subclinical" always implies that T3 and T4 levels are within the normal reference range, with only TSH being abnormal.
17. Thyroid Scan Isotopes: Uses Iodine-123 (123I) or Pertechnetate (99mTc); Needle Biopsy uses cytology to screen for malignancy.

QA