Bilirrubina literally translates to "bilirubin," a medical term for a yellow pigment found in bile. It's an incredibly unique and unexpected word to find in a popular song, making it instantly memorable.
Juan Luis Guerra uses this scientific term metaphorically to describe the overwhelming physical and emotional symptoms of being deeply in love. He humorously compares the
"La Bilirrubina" turns a broken heart into a hospital visit. The narrator shows up with a mystery fever — "Oye, me dio una fiebre el otro día" [Hey, I got a fever the other day] — and gets X-rays, colored serum injections, every test the ward has, while the real diagnosis is staring the doctors in the face: "Y me diagnosticaron mal de amores" [And they diagnosed me with lovesickness]. There's only one prescription that works: "Sólo tus besos, vida mía" [Only your kisses, my love].
The hook turns a real liver enzyme into a symptom of infatuation — "Que me ha subido la bilirrubina" [My bilirubin has gone up] — a joke Juan Luis Guerra builds an entire merengue around, right down to asking for a catheter and "vitamina de cariño" [a vitamin of affection] instead of medicine. It's from 1990's Bachata Rosa, and the absurd hospital conceit is exactly what made the chorus stick.