An infant maintained for several weeks on a fat-free parenteral nutrition regimen develops a dry, scaly, desquamating dermatitis, thrombocytopenia, and poor wound healing. Which laboratory finding best confirms essential fatty acid deficiency?

• A Serum arachidonic acid level above 20 percent of total fatty acids
• B Triene to tetraene ratio greater than 0.4 ✓
• C Low serum albumin below 2.5 g/dL
• D Elevated serum cholesterol with low triglycerides

Explanation

Essential fatty acid deficiency arises when linoleic acid intake is absent for weeks. Linoleic acid normally suppresses oleic acid desaturation to eicosatrienoic acid, so its absence raises eicosatrienoic acid while arachidonic acid falls. A triene to tetraene ratio above 0.4 is the biochemical hallmark confirming the diagnosis. Clinical features include scaly dermatitis, thrombocytopenia, poor wound healing, and growth failure. Hypoalbuminemia reflects protein status, and cholesterol changes are not diagnostic of fatty acid deficiency.

Reference: Nelson Textbook of Pediatrics, 21st ed.

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