Diagnostic Procedures & Interpretation Flashcards

Which condition can falsely elevate serum prealbumin (transthyretin) in an older adult, masking poor nutritional status?

Answer: Chronic kidney disease

Reduced renal clearance in chronic kidney disease raises prealbumin regardless of nutritional status.

An 80-year-old has a borderline serum vitamin B12 of 250 pg/mL and mild neuropathy. Which test best confirms functional B12 deficiency?

Answer: Methylmalonic acid

Elevated methylmalonic acid is a specific marker of B12 deficiency, whereas homocysteine also rises with folate deficiency.

Which situation is most likely to produce a falsely LOW hemoglobin A1c in an older adult with diabetes?

Answer: Recent blood transfusion

Transfused red cells have not been exposed to the patient's glucose, so A1c is falsely lowered.

A nursing home resident has BUN 48 mg/dL and creatinine 1.6 mg/dL. The BUN:creatinine ratio most strongly suggests:

Answer: Dehydration or prerenal azotemia

A BUN:creatinine ratio above 20:1 (here 30:1) typically indicates volume depletion or a prerenal cause.

An older adult has total serum calcium of 7.6 mg/dL and albumin of 2.0 g/dL. What is the albumin-corrected calcium?

Answer: 9.2 mg/dL

Corrected Ca = 7.6 + 0.8 × (4.0 − 2.0) = 9.2 mg/dL, which is within normal range.

An older adult with rheumatoid arthritis has microcytic anemia and a ferritin of 150 ng/mL. Which test best helps identify coexisting iron deficiency?

Answer: Soluble transferrin receptor

Soluble transferrin receptor rises in iron deficiency but is largely unaffected by inflammation, unlike ferritin.

Which laboratory measure best reflects overall vitamin D status in a homebound older adult?

Answer: 25-hydroxyvitamin D

25-hydroxyvitamin D is the main circulating form and the accepted indicator of vitamin D stores.