What does a neutrophil ‘left shift’ mean, and how specific is it for bacterial infection?

It means increased immature neutrophil forms, such as bands and metamyelocytes, in circulating blood. It can accompany bacterial infection, but also noninfectious inflammation, tissue injury or marrow disorders. It does not by itself diagnose bacterial infection or sepsis; >10% bands is a historical SIRS threshold, not a universal definition of every left shift.

How is the serum anion gap calculated without potassium, and why is its reference range not universal?

Anion gap = [Na+] − ([Cl−] + [HCO3−]), using concentrations in the same units, usually mmol/L. The laboratory method and whether potassium is included affect the reference interval. Use the reporting laboratory’s range. Low albumin lowers the gap and can conceal an otherwise elevated gap; interpret it with albumin and the acid–base findings.

How do serum and urine osmolality help evaluate hyponatremia?

Serum osmolality 100 indicates urine is not maximally dilute. Interpret paired urine sodium, kidney function, medicines and volume status. Urine osmolality alone does not establish SIADH.

What do dysmorphic red cells, red-cell casts and white-cell casts suggest on urine microscopy?

Dysmorphic red cells, especially acanthocytes, and red-cell casts support a glomerular source of bleeding, often glomerulonephritis. White-cell casts indicate inflammation within the kidney and can occur in pyelonephritis, interstitial nephritis and some glomerular diseases. Their absence does not exclude these conditions, and white-cell casts alone do not distinguish infection from sterile inflammation.

What is pulse pressure, and what can widened or narrowed pulse pressure suggest?

Pulse pressure = systolic BP − diastolic BP. Widening can reflect arterial stiffness, aortic regurgitation or a hyperdynamic circulation. Narrowing can accompany low stroke volume, as in hypovolemia, severe heart failure or tamponade. Interpret it with age, blood pressure and the clinical setting; a single pulse-pressure cutoff does not diagnose these conditions.

How do C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) differ as markers of inflammation?

CRP is an acute-phase protein made by the liver and generally rises and falls faster than ESR. ESR measures red-cell settling and is influenced by plasma proteins, anemia, age and other factors. Both are nonspecific: neither identifies the cause of inflammation alone, and a normal result does not exclude every inflammatory disease.

What typical hemodynamic patterns distinguish hypovolemic, left-ventricular cardiogenic and early hyperdynamic septic shock?

Hypovolemia: low filling pressures and cardiac output, usually high systemic vascular resistance (SVR). Left-ventricular cardiogenic shock: high pulmonary capillary wedge pressure, low output and usually high SVR; central venous pressure can vary. Hyperdynamic septic shock: low SVR and often high output, with variable, often low or normal filling pressures. Mixed disease, ventilation and treatment can alter these patterns.

What adult ECG finding defines first-degree atrioventricular (AV) block?

A PR interval >200 ms with every P wave conducted to a QRS complex. The usual adult PR range is about 120–200 ms, or 3–5 small boxes at 25 mm/s. Conduction is delayed, often in the AV node, but the delay can occur elsewhere in the atrial/His–Purkinje conduction pathway.

How is Winter’s formula used in metabolic acidosis?

Expected PaCO2 ≈ 1.5 × [HCO3−] + 8 ±2 mmHg, with bicarbonate in mmol/L. A measured PaCO2 above this range suggests additional respiratory acidosis; a value below it suggests additional respiratory alkalosis. This estimates the expected respiratory compensation for metabolic acidosis; it is not a formula for every acid–base disorder.

What approximate arterial blood gas (ABG) ranges are commonly used for an adult breathing room air at sea level?

pH 7.35–7.45; PaCO2 35–45 mmHg; bicarbonate about 22–26 mmol/L; PaO2 about 80–100 mmHg in a healthy younger adult. Use the laboratory’s reference intervals. PaO2 depends particularly on age, altitude and inspired oxygen; these are not universal oxygenation targets for every patient.

How do hypertrophy, hyperplasia, atrophy and metaplasia differ?

Hypertrophy increases cell size; hyperplasia increases cell number. Atrophy reduces cell size and may also reduce cell number in a tissue. Metaplasia is a potentially reversible replacement of one differentiated cell type by another, often in response to chronic irritation or stress. It is not the same as malignant transformation.

What can increase the blood urea nitrogen-to-creatinine (BUN:Cr) ratio, and why is a ratio above 20:1 not diagnostic?

When both are measured in mg/dL, a ratio >20:1 can occur with reduced renal perfusion, upper gastrointestinal bleeding, high protein intake or increased protein catabolism, including glucocorticoid effects. Creatinine production also depends on muscle mass. The ratio is a contextual clue, not a stand-alone test for dehydration, prerenal injury or a bleeding source.

What mechanisms distinguish unconjugated from conjugated hyperbilirubinemia?

Unconjugated bilirubin rises with increased production, such as hemolysis, or impaired hepatic uptake or conjugation, such as Gilbert syndrome. Conjugated bilirubin rises when biliary excretion is impaired, as in bile-duct obstruction, hepatocellular disease or inherited transport defects such as Dubin–Johnson syndrome. Mixed patterns occur; the fraction alone does not identify a specific disease.

How does the alveolar–arterial (A–a) oxygen gradient help classify hypoxemia?

It is alveolar PO2 minus arterial PO2. A gradient within the expected range for age and inspired oxygen supports hypoventilation or low inspired oxygen tension. An increased gradient supports ventilation–perfusion mismatch, right-to-left shunt or diffusion limitation. Mechanisms can coexist; a fixed 10–15 mmHg cutoff is not appropriate for every age or oxygen concentration.

What do PT/INR and aPTT assess, and which anticoagulants are commonly monitored with them?

PT assesses the extrinsic and common coagulation pathways; its standardized INR is used to monitor warfarin. aPTT assesses the intrinsic and common pathways and can monitor intravenous unfractionated heparin; a calibrated anti-Xa assay is an alternative under local protocols. These are laboratory pathway tests, and neither reliably quantifies every anticoagulant’s effect.

What are key collection principles for routine adult blood cultures in suspected bloodstream infection?

Obtain at least two sets from separate venipuncture sites using aseptic technique and adequate blood volume; a set usually includes aerobic and anaerobic bottles. Collect promptly and preferably before antimicrobials. Do not postpone urgent antimicrobial treatment in an unstable patient or suspected septic shock merely to complete culture collection. Follow the institution’s collection protocol.

How do coagulative and liquefactive necrosis differ, and where are they typically found?

Coagulative necrosis involves protein denaturation with temporary preservation of tissue outlines; it is typical of ischemic infarcts in most solid organs, such as the heart and kidney. Brain infarcts usually undergo liquefactive necrosis, in which enzymatic digestion destroys the architecture. Liquefaction also occurs in many bacterial abscesses.

What three factors make up Virchow’s triad of thrombosis?

Endothelial injury or dysfunction, abnormal blood flow such as stasis or turbulence, and hypercoagulability. They describe mechanisms that favor thrombosis; all three need not be demonstrable in every patient. Venous stasis during prolonged immobility is one example.

What are the Glasgow Coma Scale (GCS) components, and how does a low score affect adult head-injury airway assessment?

Eye opening scores 1–4, verbal response 1–5 and motor response 1–6; total 3–15 when all components are testable. GCS ≤8 requires urgent skilled airway assessment. Coma, lost protective reflexes or inadequate ventilation indicate intubation; NICE recommends it before neuroscience transfer when GCS ≤8. Record component scores, trends and confounders such as sedation; mark untestable components rather than inventing a score.

How should AST-predominant and ALT-predominant aminotransferase elevations be interpreted?

AST:ALT >2 can suggest alcohol-associated liver disease in the appropriate history, but does not establish it. ALT predominance can occur in metabolic dysfunction–associated steatotic liver disease (MASLD) or viral hepatitis. Cirrhosis from other causes and muscle injury can also raise AST disproportionately. Interpret the pattern with the absolute levels, history and other investigations.

What does a QRS duration of at least 120 ms mean on an adult ECG?

It is a wide QRS, at least three small boxes at 25 mm/s, reflecting prolonged or abnormal ventricular activation. Causes include bundle-branch block, ventricular rhythms or pacing, pre-excitation, hyperkalemia and sodium-channel–blocking drugs. QRS duration alone does not identify the cause.

What are the classic adult systemic inflammatory response syndrome (SIRS) criteria, and do they establish sepsis?

At least two: temperature >38°C or 90/min; respiratory rate >20/min or PaCO2 12,000/µL, 10% immature forms. SIRS can follow infectious or noninfectious insults. It is neither sufficient nor necessary for the Sepsis-3 definition of sepsis.

How is mean arterial pressure (MAP) estimated, and what initial target does the 2026 Surviving Sepsis Campaign recommend in adult septic shock?

At a normal resting heart rate, MAP ≈ DBP + (SBP − DBP)/3, where SBP and DBP are systolic and diastolic blood pressure. The guideline recommends an initial MAP of 65 mmHg; for adults aged ≥65 years, it conditionally suggests 60–65 mmHg. Reassess perfusion and individualize subsequent targets; these are not targets for every type of shock.

How is anemia commonly classified by mean corpuscular volume (MCV) in adults?

Microcytic: MCV 100 fL, as in vitamin B12 or folate deficiency. These are patterns, not diagnoses; mixed disorders can yield a normal average MCV. Use age-appropriate laboratory ranges.

How is prolonged QTc recognized in adults, and what arrhythmia risk does it signal?

Common upper limits are about 450 ms in men and 460 ms in women, but thresholds depend on the correction method and clinical context. QTc >500 ms is associated with greater torsades de pointes risk. Torsades is a polymorphic ventricular tachycardia that can deteriorate into ventricular fibrillation; QT prolongation does not mean it will inevitably occur.

What triggers BNP release, and how do natriuretic peptides help evaluate suspected acute heart failure?

Myocardial wall stress stimulates BNP release. In new suspected acute heart failure, BNP <100 pg/mL or NT-proBNP <300 pg/mL supports exclusion within a clinical diagnostic pathway. Obesity can lower concentrations; renal dysfunction and atrial fibrillation can raise them. Elevated values alone do not establish heart failure, and persistent clinical suspicion warrants further assessment.

Under the adult Sepsis-3 definitions, how do sepsis and septic shock differ?

Sepsis is life-threatening organ dysfunction from a dysregulated response to infection; an acute SOFA increase of ≥2 points attributable to infection operationalizes organ dysfunction. Septic shock is the subset requiring vasopressors to maintain MAP ≥65 mmHg, with lactate >2 mmol/L despite adequate volume resuscitation. These definitions are distinct from a screening score or an individualized treatment target.

What standard blood-pressure change defines classical orthostatic hypotension in adults?

A sustained fall in systolic BP of ≥20 mmHg or diastolic BP of ≥10 mmHg within 3 minutes of standing. The usual assessment starts after at least 5 minutes supine; seated-to-standing testing is less sensitive. Symptoms may be absent, and a normal 3-minute test does not exclude delayed orthostatic hypotension.

What is fractional excretion of sodium (FeNa), and what are its diagnostic limitations in acute kidney injury?

FeNa is the percentage of filtered sodium excreted: 100 × (urine Na × plasma creatinine)/(plasma Na × urine creatinine), with matched concentration units. 2% can support tubular injury. Neither is diagnostic. Diuretics and chronic kidney disease reduce reliability, and some intrinsic injuries have FeNa <1%. Interpret with the clinical course and urine sediment.

When can a D-dimer result help exclude venous thromboembolism (VTE)?

A negative high-sensitivity result can exclude VTE within a validated low/unlikely-probability pathway; some pulmonary-embolism pathways also include intermediate probability. Use the assay-specific cutoff, often 500 ng/mL FEU, or age ×10 ng/mL FEU in eligible outpatients over 50. FEU and DDU units differ. A positive result is not diagnostic; high clinical probability requires an imaging-based pathway.

How do serial cardiac troponin results distinguish myocardial injury from myocardial infarction?

Troponin above the assay’s 99th-percentile upper reference limit indicates myocardial injury; use sex-specific limits where validated. A significant rise or fall supports acute injury. Infarction also requires evidence of ischemia, such as compatible symptoms, ECG changes or imaging. Interpret serial results with an assay-specific pathway; a single elevated or early normal result is insufficient by itself.

What major categories cause high-anion-gap metabolic acidosis?

Lactic acidosis; ketoacidosis from diabetes, alcohol-related illness or starvation; advanced kidney failure with retained acids; and certain toxic exposures, including methanol, ethylene glycol and salicylates. These processes add or retain acids whose anions are not included in the routine gap calculation. The pattern narrows the differential but does not identify the cause by itself.

Pathophysiology, Hemodynamics & Diagnostic Test Interpretation

32 pathology and clinical-foundations review cards on vital signs, shock states, sepsis, cellular adaptation, reversible versus irreversible injury, necrosis, apoptosis, inflammation, edema, anemia, coagulation, acid–base balance, electrolyte panels, urinalysis, ECG intervals, and Glasgow Coma Scale.

Level: basic
Languages: en → en
Cards: 32
Markdown: Pathophysiology, Hemodynamics & Diagnostic Test Interpretation (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	What does a neutrophil ‘left shift’ mean, and how specific is it for bacterial infection?	It means increased immature neutrophil forms, such as bands and metamyelocytes, in circulating blood. It can accompany bacterial infection, but also noninfectious inflammation, tissue injury or marrow disorders. It does not by itself diagnose bacterial infection or sepsis; >10% bands is a historical SIRS threshold, not a universal definition of every left shift.
2	How is the serum anion gap calculated without potassium, and why is its reference range not universal?	Anion gap = [Na+] − ([Cl−] + [HCO3−]), using concentrations in the same units, usually mmol/L. The laboratory method and whether potassium is included affect the reference interval. Use the reporting laboratory’s range. Low albumin lowers the gap and can conceal an otherwise elevated gap; interpret it with albumin and the acid–base findings.
3	How do serum and urine osmolality help evaluate hyponatremia?	Serum osmolality <275 mOsm/kg identifies hypotonic hyponatremia; distinguish this from hyperglycemia-related hypertonicity and pseudohyponatremia. In hypotonic hyponatremia, urine osmolality ≤100 mOsm/kg supports excess water intake relative to solute intake; >100 indicates urine is not maximally dilute. Interpret paired urine sodium, kidney function, medicines and volume status. Urine osmolality alone does not establish SIADH.
4	What do dysmorphic red cells, red-cell casts and white-cell casts suggest on urine microscopy?	Dysmorphic red cells, especially acanthocytes, and red-cell casts support a glomerular source of bleeding, often glomerulonephritis. White-cell casts indicate inflammation within the kidney and can occur in pyelonephritis, interstitial nephritis and some glomerular diseases. Their absence does not exclude these conditions, and white-cell casts alone do not distinguish infection from sterile inflammation.
5	What is pulse pressure, and what can widened or narrowed pulse pressure suggest?	Pulse pressure = systolic BP − diastolic BP. Widening can reflect arterial stiffness, aortic regurgitation or a hyperdynamic circulation. Narrowing can accompany low stroke volume, as in hypovolemia, severe heart failure or tamponade. Interpret it with age, blood pressure and the clinical setting; a single pulse-pressure cutoff does not diagnose these conditions.
6	How do C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) differ as markers of inflammation?	CRP is an acute-phase protein made by the liver and generally rises and falls faster than ESR. ESR measures red-cell settling and is influenced by plasma proteins, anemia, age and other factors. Both are nonspecific: neither identifies the cause of inflammation alone, and a normal result does not exclude every inflammatory disease.
7	What typical hemodynamic patterns distinguish hypovolemic, left-ventricular cardiogenic and early hyperdynamic septic shock?	Hypovolemia: low filling pressures and cardiac output, usually high systemic vascular resistance (SVR). Left-ventricular cardiogenic shock: high pulmonary capillary wedge pressure, low output and usually high SVR; central venous pressure can vary. Hyperdynamic septic shock: low SVR and often high output, with variable, often low or normal filling pressures. Mixed disease, ventilation and treatment can alter these patterns.
8	What adult ECG finding defines first-degree atrioventricular (AV) block?	A PR interval >200 ms with every P wave conducted to a QRS complex. The usual adult PR range is about 120–200 ms, or 3–5 small boxes at 25 mm/s. Conduction is delayed, often in the AV node, but the delay can occur elsewhere in the atrial/His–Purkinje conduction pathway.
9	How is Winter’s formula used in metabolic acidosis?	Expected PaCO2 ≈ 1.5 × [HCO3−] + 8 ±2 mmHg, with bicarbonate in mmol/L. A measured PaCO2 above this range suggests additional respiratory acidosis; a value below it suggests additional respiratory alkalosis. This estimates the expected respiratory compensation for metabolic acidosis; it is not a formula for every acid–base disorder.
10	What approximate arterial blood gas (ABG) ranges are commonly used for an adult breathing room air at sea level?	pH 7.35–7.45; PaCO2 35–45 mmHg; bicarbonate about 22–26 mmol/L; PaO2 about 80–100 mmHg in a healthy younger adult. Use the laboratory’s reference intervals. PaO2 depends particularly on age, altitude and inspired oxygen; these are not universal oxygenation targets for every patient.
11	How do hypertrophy, hyperplasia, atrophy and metaplasia differ?	Hypertrophy increases cell size; hyperplasia increases cell number. Atrophy reduces cell size and may also reduce cell number in a tissue. Metaplasia is a potentially reversible replacement of one differentiated cell type by another, often in response to chronic irritation or stress. It is not the same as malignant transformation.
12	What can increase the blood urea nitrogen-to-creatinine (BUN:Cr) ratio, and why is a ratio above 20:1 not diagnostic?	When both are measured in mg/dL, a ratio >20:1 can occur with reduced renal perfusion, upper gastrointestinal bleeding, high protein intake or increased protein catabolism, including glucocorticoid effects. Creatinine production also depends on muscle mass. The ratio is a contextual clue, not a stand-alone test for dehydration, prerenal injury or a bleeding source.
13	What mechanisms distinguish unconjugated from conjugated hyperbilirubinemia?	Unconjugated bilirubin rises with increased production, such as hemolysis, or impaired hepatic uptake or conjugation, such as Gilbert syndrome. Conjugated bilirubin rises when biliary excretion is impaired, as in bile-duct obstruction, hepatocellular disease or inherited transport defects such as Dubin–Johnson syndrome. Mixed patterns occur; the fraction alone does not identify a specific disease.
14	How does the alveolar–arterial (A–a) oxygen gradient help classify hypoxemia?	It is alveolar PO2 minus arterial PO2. A gradient within the expected range for age and inspired oxygen supports hypoventilation or low inspired oxygen tension. An increased gradient supports ventilation–perfusion mismatch, right-to-left shunt or diffusion limitation. Mechanisms can coexist; a fixed 10–15 mmHg cutoff is not appropriate for every age or oxygen concentration.
15	What do PT/INR and aPTT assess, and which anticoagulants are commonly monitored with them?	PT assesses the extrinsic and common coagulation pathways; its standardized INR is used to monitor warfarin. aPTT assesses the intrinsic and common pathways and can monitor intravenous unfractionated heparin; a calibrated anti-Xa assay is an alternative under local protocols. These are laboratory pathway tests, and neither reliably quantifies every anticoagulant’s effect.
16	What are key collection principles for routine adult blood cultures in suspected bloodstream infection?	Obtain at least two sets from separate venipuncture sites using aseptic technique and adequate blood volume; a set usually includes aerobic and anaerobic bottles. Collect promptly and preferably before antimicrobials. Do not postpone urgent antimicrobial treatment in an unstable patient or suspected septic shock merely to complete culture collection. Follow the institution’s collection protocol.
17	How do coagulative and liquefactive necrosis differ, and where are they typically found?	Coagulative necrosis involves protein denaturation with temporary preservation of tissue outlines; it is typical of ischemic infarcts in most solid organs, such as the heart and kidney. Brain infarcts usually undergo liquefactive necrosis, in which enzymatic digestion destroys the architecture. Liquefaction also occurs in many bacterial abscesses.
18	What three factors make up Virchow’s triad of thrombosis?	Endothelial injury or dysfunction, abnormal blood flow such as stasis or turbulence, and hypercoagulability. They describe mechanisms that favor thrombosis; all three need not be demonstrable in every patient. Venous stasis during prolonged immobility is one example.
19	What are the Glasgow Coma Scale (GCS) components, and how does a low score affect adult head-injury airway assessment?	Eye opening scores 1–4, verbal response 1–5 and motor response 1–6; total 3–15 when all components are testable. GCS ≤8 requires urgent skilled airway assessment. Coma, lost protective reflexes or inadequate ventilation indicate intubation; NICE recommends it before neuroscience transfer when GCS ≤8. Record component scores, trends and confounders such as sedation; mark untestable components rather than inventing a score.
20	How should AST-predominant and ALT-predominant aminotransferase elevations be interpreted?	AST:ALT >2 can suggest alcohol-associated liver disease in the appropriate history, but does not establish it. ALT predominance can occur in metabolic dysfunction–associated steatotic liver disease (MASLD) or viral hepatitis. Cirrhosis from other causes and muscle injury can also raise AST disproportionately. Interpret the pattern with the absolute levels, history and other investigations.
21	What does a QRS duration of at least 120 ms mean on an adult ECG?	It is a wide QRS, at least three small boxes at 25 mm/s, reflecting prolonged or abnormal ventricular activation. Causes include bundle-branch block, ventricular rhythms or pacing, pre-excitation, hyperkalemia and sodium-channel–blocking drugs. QRS duration alone does not identify the cause.
22	What are the classic adult systemic inflammatory response syndrome (SIRS) criteria, and do they establish sepsis?	At least two: temperature >38°C or <36°C; heart rate >90/min; respiratory rate >20/min or PaCO2 <32 mmHg; white-cell count >12,000/µL, <4,000/µL or >10% immature forms. SIRS can follow infectious or noninfectious insults. It is neither sufficient nor necessary for the Sepsis-3 definition of sepsis.
23	How is mean arterial pressure (MAP) estimated, and what initial target does the 2026 Surviving Sepsis Campaign recommend in adult septic shock?	At a normal resting heart rate, MAP ≈ DBP + (SBP − DBP)/3, where SBP and DBP are systolic and diastolic blood pressure. The guideline recommends an initial MAP of 65 mmHg; for adults aged ≥65 years, it conditionally suggests 60–65 mmHg. Reassess perfusion and individualize subsequent targets; these are not targets for every type of shock.
24	How is anemia commonly classified by mean corpuscular volume (MCV) in adults?	Microcytic: MCV <80 fL, as in iron deficiency or thalassemia. Normocytic: 80–100 fL, as in acute blood loss or chronic kidney disease. Macrocytic: >100 fL, as in vitamin B12 or folate deficiency. These are patterns, not diagnoses; mixed disorders can yield a normal average MCV. Use age-appropriate laboratory ranges.
25	How is prolonged QTc recognized in adults, and what arrhythmia risk does it signal?	Common upper limits are about 450 ms in men and 460 ms in women, but thresholds depend on the correction method and clinical context. QTc >500 ms is associated with greater torsades de pointes risk. Torsades is a polymorphic ventricular tachycardia that can deteriorate into ventricular fibrillation; QT prolongation does not mean it will inevitably occur.
26	What triggers BNP release, and how do natriuretic peptides help evaluate suspected acute heart failure?	Myocardial wall stress stimulates BNP release. In new suspected acute heart failure, BNP <100 pg/mL or NT-proBNP <300 pg/mL supports exclusion within a clinical diagnostic pathway. Obesity can lower concentrations; renal dysfunction and atrial fibrillation can raise them. Elevated values alone do not establish heart failure, and persistent clinical suspicion warrants further assessment.
27	Under the adult Sepsis-3 definitions, how do sepsis and septic shock differ?	Sepsis is life-threatening organ dysfunction from a dysregulated response to infection; an acute SOFA increase of ≥2 points attributable to infection operationalizes organ dysfunction. Septic shock is the subset requiring vasopressors to maintain MAP ≥65 mmHg, with lactate >2 mmol/L despite adequate volume resuscitation. These definitions are distinct from a screening score or an individualized treatment target.
28	What standard blood-pressure change defines classical orthostatic hypotension in adults?	A sustained fall in systolic BP of ≥20 mmHg or diastolic BP of ≥10 mmHg within 3 minutes of standing. The usual assessment starts after at least 5 minutes supine; seated-to-standing testing is less sensitive. Symptoms may be absent, and a normal 3-minute test does not exclude delayed orthostatic hypotension.
29	What is fractional excretion of sodium (FeNa), and what are its diagnostic limitations in acute kidney injury?	FeNa is the percentage of filtered sodium excreted: 100 × (urine Na × plasma creatinine)/(plasma Na × urine creatinine), with matched concentration units. <1% can support prerenal physiology; >2% can support tubular injury. Neither is diagnostic. Diuretics and chronic kidney disease reduce reliability, and some intrinsic injuries have FeNa <1%. Interpret with the clinical course and urine sediment.
30	When can a D-dimer result help exclude venous thromboembolism (VTE)?	A negative high-sensitivity result can exclude VTE within a validated low/unlikely-probability pathway; some pulmonary-embolism pathways also include intermediate probability. Use the assay-specific cutoff, often 500 ng/mL FEU, or age ×10 ng/mL FEU in eligible outpatients over 50. FEU and DDU units differ. A positive result is not diagnostic; high clinical probability requires an imaging-based pathway.
31	How do serial cardiac troponin results distinguish myocardial injury from myocardial infarction?	Troponin above the assay’s 99th-percentile upper reference limit indicates myocardial injury; use sex-specific limits where validated. A significant rise or fall supports acute injury. Infarction also requires evidence of ischemia, such as compatible symptoms, ECG changes or imaging. Interpret serial results with an assay-specific pathway; a single elevated or early normal result is insufficient by itself.
32	What major categories cause high-anion-gap metabolic acidosis?	Lactic acidosis; ketoacidosis from diabetes, alcohol-related illness or starvation; advanced kidney failure with retained acids; and certain toxic exposures, including methanol, ethylene glycol and salicylates. These processes add or retain acids whose anions are not included in the routine gap calculation. The pattern narrows the differential but does not identify the cause by itself.