Hoesch test

Qualitative screening tests in which urine is reacted directly with Ehrlich s reagent and assessed visually for the formation of the red chromogen (e.g., the Watson-Schwartz and Hoesch tests) are convenient but have been criticized for poor detection limits and interferences, even when solvent extraction has been used to separate the PBG-Ehrlich compound from the urobilinogen-Ehrfich complex. ... 

Lamon J, With T, Redeker A. The Hoesch test bedside screening for urinary PBG inpatients with suspected porphyria. Clin Chem. 1974 20 1438-40. 

Screening tests for PBG are based on its reaction with DMAB (modified Ehrlichs reaction ). We recommend the trace PBG test kit available from Thermo Electron (UK), which isolates PBG from urine by ion-exchange resin before the reaction with DMAB. Older screening methods, such as those of Schwartz or Hoesch, give false-positive results due to the reaction of DMAB with urea, which is abundant in urine. 

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