Nitrazine

Nitrazine refers to a pH indicator used in nitrazine paper, a diagnostic strip used to test acidity or alkalinity of fluids. The indicator shifts color depending on pH, turning yellow in acidic environments and blue in alkaline ones.

In obstetrics, nitrazine paper is used to assess rupture of membranes. Amniotic fluid is more alkaline than normal vaginal secretions, so when a sample of vaginal discharge is applied to the strip, a blue color suggests alkaline pH consistent with amniotic fluid, while yellow or greenish colors indicate acidic vaginal secretions.

Procedure and interpretation: A clinician applies a few drops of the fluid on the nitrazine-impregnated strip or uses the strip directly on the sample; color is compared to a reference card after a short interval. Blue typically indicates pH above around 7, though exact thresholds vary by product.

Limitations: The nitrazine test is rapid but not definitive. Semen, vaginal infections, blood, cleansers, or recent intercourse can alter color and yield false positives or negatives. For amniotic fluid assessment, a positive nitrazine test is usually followed by additional testing, such as fern test or analysis for specific proteins.