Chemistry Panels, Electrolytes & Acid-Base Balance Lecture

Flashcards cover core laboratory values, electrolyte roles and disorders, acid–base disturbances, glucose metabolism, diabetes diagnostics, and related compensatory mechanisms.

What electrolytes and chemistries are included in a Basic Metabolic Panel (BMP)?

Na, K, Cl, CO2 (HCO3-), anion gap, BUN, creatinine, glucose, calcium, eGFR.

Which additional tests turn a BMP into a Comprehensive Metabolic Panel (CMP)?

Liver function tests—AST, ALT, ALP, total protein, albumin, globulin (with A/G ratio), and total bilirubin.

What is the normal reference range for serum sodium?

135–145 mEq/L

What hormone pair primarily regulates serum sodium through the kidney?

Antidiuretic hormone (ADH) and aldosterone

Below what sodium level do hyponatremia symptoms commonly appear?

< 120 mEq/L

Name three classic symptoms of hyponatremia.

Nausea, generalized weakness, altered mental status

What distinguishes hypovolemic hyponatremia from normovolemic hyponatremia?

In hypovolemic hyponatremia both water and Na are lost but Na loss is greater; in normovolemic hyponatremia total body water increases while total body Na stays the same (dilution).

Give two causes of hypovolemic hyponatremia.

GI fluid loss with hypotonic replacement; thiazide diuretics; burns (any two).

Give two causes of normovolemic hyponatremia.

SIADH, severe hyperglycemia, primary polydipsia, hypothyroidism (any two).

What are two common causes of hypervolemic hyponatremia?

Congestive heart failure and hepatic cirrhosis (others: nephrotic syndrome, renal failure, over-hydration).

What is the most common overall cause of hypernatremia?

Hypovolemic hypernatremia due to water loss > sodium loss (e.g., dehydration).

Diabetes insipidus causes which subtype of hypernatremia?

Normovolemic hypernatremia

Name two causes of hypervolemic hypernatremia.

Hypertonic saline administration, hyperaldosteronism

What is the normal reference range for serum potassium?

3.5–5 mEq/L

List two main physiologic roles of potassium.

Neuromuscular excitability and cardiac contraction (also intracellular volume regulation, acid–base exchange).

What is the most common iatrogenic cause of hypokalemia?

Use of diuretics

How does insulin administration affect serum potassium?

Drives K⁺ into cells, potentially causing hypokalemia.

Give two symptoms or complications of hyperkalemia.

Cardiac arrhythmias/arrest and muscle weakness

Name two non-renal causes of hyperkalemia.

Acidosis, excess dietary intake, insulin deficiency, drugs such as ACE inhibitors or K-sparing diuretics (any two).

What is the major extracellular anion?

Chloride (Cl⁻)

Hyperchloremia often parallels which sodium disorder?

Hypernatremia

List two causes of hyperchloremia.

Dehydration, respiratory alkalosis (hyperventilation), GI bicarbonate loss (diarrhea), renal tubular acidosis (any two).

Prolonged vomiting is most likely to cause which chloride abnormality?

Hypochloremia

Serum CO₂ on a BMP is an indirect measure of which ion?

Bicarbonate (HCO₃⁻)

Provide the formula for calculating the anion gap (without K⁺).

AG = Na⁺ – (Cl⁻ + HCO₃⁻)

What is the normal reference range for the anion gap?

8–12 mEq/L

Multiple myeloma is classically associated with what type of anion gap?

Low anion gap (rare).

List the mnemonic ‘MUDPILES’ high-anion-gap causes and give any three.

Methanol, Uremia, Diabetic ketoacidosis, Propylene glycol/Paraldehyde, Iron/Isoniazid, Lactic acidosis, Ethylene glycol/Ethanol, Salicylates/Starvation (any three).

What blood pH range is considered normal?

7.35–7.45

Which organ systems provide the primary buffers for acid-base balance?

Lungs (CO₂ excretion) and kidneys (HCO₃⁻ regulation)

Write the Henderson-Hasselbalch shortcut ratio used clinically.

pH ≈ HCO₃⁻ / pCO₂

Normal arterial pCO₂ range?

35–45 mm Hg

Normal arterial bicarbonate (HCO₃⁻) range?

22–26 mEq/L

Primary decrease in HCO₃⁻ produces which metabolic disorder?

Metabolic acidosis

Primary increase in pCO₂ produces which respiratory disorder?

Respiratory acidosis

Name two major categories of metabolic acidosis.

High anion gap metabolic acidosis (HAGMA) and normal anion gap metabolic acidosis (NAGMA).

Give two common causes of high anion gap metabolic acidosis.

Lactic acidosis, diabetic ketoacidosis, renal failure, toxic alcohols, salicylate poisoning (any two).

What mnemonic helps recall normal-anion-gap metabolic acidosis causes?

HARDUPS (Hyperalimentation, Acetazolamide, Renal tubular acidosis, Diarrhea, Uretero-pelvic shunt, Post-hypocapnia, Spironolactone).

Why does metabolic acidosis often lead to hyperkalemia?

High H⁺ shifts into cells in exchange for K⁺ shifting out, raising serum K⁺.

Loss of gastric HCl (e.g., vomiting) leads to which acid-base disorder?

Metabolic alkalosis

Metabolic alkalosis typically produces what potassium abnormality?

Hypokalemia

How does the respiratory system compensate for metabolic acidosis?

Increases ventilation to blow off CO₂, lowering pCO₂.

What ABG pattern indicates appropriate compensation for metabolic alkalosis?

Both HCO₃⁻ and pCO₂ are elevated (hypoventilation retains CO₂).

Hypoventilation resulting in CO₂ retention causes which disorder?

Respiratory acidosis

List two neurologic or pulmonary causes of respiratory acidosis.

COPD, neuromuscular weakness (ALS, Guillain-Barré), CNS depression (narcotics, anesthesia), severe kyphoscoliosis (any two).

Main physiologic compensation for chronic respiratory acidosis?

Renal reabsorption of additional bicarbonate.

Hyperventilation due to anxiety produces which acid-base disorder?

Respiratory alkalosis

How does the kidney compensate for respiratory alkalosis?

Decreases bicarbonate reabsorption (excretes HCO₃⁻).

Describe the effect of acidosis on serum potassium.

Acidosis (low pH) shifts K⁺ out of cells → hyperkalemia.

Describe the effect of alkalosis on serum potassium.

Alkalosis (high pH) shifts K⁺ into cells → hypokalemia.

What three classic symptoms make up the diabetes ‘polys’?

Polydipsia, polyuria, polyphagia

At what fasting plasma glucose level is diabetes diagnosed?

≥ 126 mg/dL on two separate occasions.

Which lab reflects average glucose control over ~3 months?

Hemoglobin A1c

What HbA1c value is diagnostic for diabetes?

6.5 % (confirmed on repeat testing).

State the physiologic actions of insulin on blood glucose.

Increases cellular uptake/storage of glucose, lowers plasma glucose.

Which counter-regulatory hormone raises blood glucose by stimulating glycogenolysis and gluconeogenesis?

Glucagon

Define gluconeogenesis.

Formation of new glucose from non-carbohydrate sources (e.g., amino acids) in the liver.

At what plasma glucose level does glucose commonly begin to spill into urine (glucosuria)?

≈ 160–180 mg/dL

What acute, high-glucose complication is characterized by ketone production and metabolic acidosis?

Diabetic ketoacidosis (DKA)

Which ketone body is often measured to help diagnose DKA?

β-Hydroxybutyrate

List the basic lab triad ordered when DKA is suspected.

CMP (electrolytes, anion gap, glucose), ABG/VBG, and urinalysis (for ketones).

What screening test is most commonly used for gestational diabetes?

1-hour 50-g oral glucose tolerance test at 24–28 weeks gestation.

How many abnormal values (out of 4) are required to confirm gestational diabetes on a 3-hour OGTT?

Two or more values at or above the cutoff.

Why does hypovolemic hyponatremia frequently occur in endurance athletes?

Sweat loss of both water and Na⁺ replaced only with hypotonic fluids, leading to greater Na⁺ loss than water.

What other electrolyte abnormality often accompanies hypovolemic hyponatremia from excessive sweating?

Hypochloremia

Complete this formula: pH = ?

pH ≈ (HCO₃⁻) / (0.03 × pCO₂) – simplified clinically to HCO₃⁻ / pCO₂ ratio.