Clinical Chemistry Flashcards

Na 140 mmol/L, Cl 100 mmol/L, HCO3 10 mmol/L. What does the anion gap suggest?

Answer: High anion gap metabolic acidosis

AG = 140 − (100 + 10) = 30, which is high and fits unmeasured acids such as lactate or ketones.

Arterial blood gas: pH 7.50, pCO2 48 mm Hg, HCO3 36 mmol/L. The interpretation is:

Answer: Partially compensated metabolic alkalosis

High pH and high HCO3 indicate metabolic alkalosis, and the raised pCO2 is respiratory compensation that hasn't brought pH back to normal.

An arterial blood gas syringe contains a large air bubble. The expected effect on results is:

Answer: Increased pO2 and decreased pCO2

Room air has a higher pO2 and almost no CO2, so the sample balances toward those values.

A severely lipemic sample shows low sodium by indirect ISE but normal sodium by direct ISE. This is best explained by:

Answer: Pseudohyponatremia from the electrolyte exclusion effect

Lipid takes up plasma volume, and diluting the sample for indirect ISE underestimates sodium in plasma water.

Which analyte is most falsely elevated by in vitro hemolysis?

Answer: Potassium

Red cells contain about 20 times more potassium than plasma, so lysis releases it into the sample.

Measured osmolality 330 mOsm/kg, calculated osmolality 290 mOsm/kg in an obtunded patient. The most likely cause is:

Answer: Ethylene glycol ingestion

An osmolal gap above about 10 points to unmeasured osmotically active substances such as toxic alcohols.

How does acute alkalosis affect serum ionized calcium?

Answer: Ionized calcium decreases

In alkalosis albumin releases H+ and binds more Ca2+, which lowers the free ionized fraction.