Which test is a qualitative screening test for porphobilinogen?

• A. Caraway test
• B. Gutmann test
• C. Jendrassik-Grof test
• D. Watson-Schwartz test

Answer: (D)

The key idea is detecting porphobilinogen in urine with a reaction that is specific enough to be used as a screening test. Porphobilinogen forms a colored compound with Ehrlich’s reagent, so a simple Ehrlich-based test can signal its presence. The Watson-Schwartz approach adds an important step: it partitions the sample with an organic solvent after the Ehrlich’s reaction. Porphobilinogen migrates into the organic layer, while most interfering substances (like urobilinogen) do not. Observing the red color in the organic layer indicates porphobilinogen is present, giving a positive, qualitative screen for porphyria.

The other tests listed are not the standard qualitative screening for porphobilinogen; they either don’t include this selective partitioning step or aren’t used specifically for PBG screening, so they’re not as reliable for this purpose.