A patient on prolonged parenteral nutrition lacking lipid emulsion develops scaly dermatitis, poor wound healing, and thrombocytopenia. Which biochemical finding confirms essential fatty acid deficiency?
- A Elevated urinary methylmalonic acid
- B Decreased plasma sphingomyelin with elevated ceramide
- C Elevated plasma eicosatrienoic acid with triene to tetraene ratio greater than 0.4 ✓
- D Reduced erythrocyte transketolase activity
Correct answer: C. Elevated plasma eicosatrienoic acid with triene to tetraene ratio greater than 0.4
Explanation
Linoleic acid cannot be synthesised in humans and must come from diet. In its absence, oleic acid is desaturated abnormally to eicosatrienoic acid (Mead acid), and a triene to tetraene ratio above 0.4 is the classic confirmatory marker. Methylmalonic acid rises in vitamin B12 deficiency, and reduced transketolase activity indicates thiamine deficiency, so both are unrelated to fatty acid biochemistry. Sphingomyelin changes are not a marker used for this diagnosis.
Reference: Harper's Illustrated Biochemistry, 31st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.