Add 1ml of sterile saline  to the culture slant. If growth is confluent, puncture the medium with a Pasteur pipette  to allow contact of the saline with the medium

Place the tube horizontally  so the fluid covers the entire surface of the medium

Allow 30 minutes for the extraction of niacin. The extraction time may be longer if the culture has few colonies

Raise the slant upright for  5 minutes to allow the fluid to drain to the bottom. Remove 0.5ml of the fluid extract to a clean screwcap tube

Insert the strip with the  identification end up (an arrow may indicate which end to insert first) and immediately seal the tube. Do not let the middle of the strip get wet

Leave at room temperature  for 15-20 minutes.  Occasionally agitate the tube without tilting it

Observe the colour of the  liquid in the bottom of the tube against a white background (yellow = positive). Discard  any colour on the strip itself; this may occur because of oxidation of chemicals, especially at the top of the strip

Neutralise the strips with 10% sodium hydroxide or discard them into alkaline disinfectant