Diagnostic Procedures & Interpretation Flashcards

An older adult has Na 150 mEq/L, glucose 180 mg/dL, and BUN 42 mg/dL. The calculated serum osmolality is about:

Answer: 325 mOsm/kg

2(150) + 180/18 + 42/2.8 = 300 + 10 + 15 = 325 mOsm/kg, indicating hyperosmolar dehydration.

Which electrolyte abnormality is the hallmark lab finding of refeeding syndrome in a malnourished older adult?

Answer: Hypophosphatemia

Insulin release during refeeding moves phosphate into cells, causing hypophosphatemia.

Under EWGSOP2, which usual gait speed indicates low physical performance and severe sarcopenia when strength and mass are also low?

Answer: ≤0.8 m/s

EWGSOP2 uses gait speed of 0.8 m/s or less as the cutoff for low physical performance.

When interpreting a low serum zinc level in an older adult with a nonhealing pressure injury, the RD should also consider that:

Answer: Low serum albumin can lower measured zinc

Most circulating zinc is bound to albumin, and inflammation also lowers serum zinc, so low values may not reflect true deficiency.

Which folate measure best reflects long-term folate status in an older adult with irregular intake?

Answer: Red blood cell folate

RBC folate reflects stores over the RBC lifespan, whereas serum folate reflects recent intake.

Indirect calorimetry in a tube-fed older patient shows a respiratory quotient of 1.1. This most likely indicates:

Answer: Overfeeding with lipogenesis

An RQ above 1.0 indicates net lipogenesis, usually from excess calorie or carbohydrate delivery.

Why can serum creatinine-based eGFR overestimate kidney function in a frail older adult with low muscle mass, and which marker is less affected?

Answer: Low creatinine production; cystatin C

Low muscle mass reduces creatinine production, while cystatin C is largely independent of muscle mass.