Module 12: Intro to Mastitis Testing

Module 12.2: Detecting Subclinical Mastitis

Detecting subclinical mastitis

California Mastitis Test (CMT)

The California Mastitis Test (CMT) is a patient-side, rapid test for detecting subclinical mastitis in individual animals. We do not use the CMT on animals with clinical mastitis. Other tests such as the Portacheck Somatic Cell Counts (SCC) and IDEXX SCC are also available, but the CMT is still the most common test used by the producer because it is easy, fast, and inexpensive. The CMT uses a specific reagent that lyses the white blood cells (WBC) present in the milk. When WBC counts reach above 200,000 cells per milliliter the lysing of the WBCs and the reagent begin to form a gel.


California Mastitis Paddle
CMT Reagent
2cc of milk from each quarter


  1. Take about 1 teaspoon (2 cc) milk from each quarter. This is the amount of milk that would be left in the cups if the CMT Paddle were held nearly vertical – the milk should come up to the outside line on the bottom of the cup when held nearly vertical.
  2. Add an equal amount of CMT solution to each cup in the paddle. (roughly 2cc reagent)
  3. Rotate the CMT Paddle in a circular motion to thoroughly mix the contents. Do not mix more than 10 seconds.
  4. Read the test quickly. The visible reaction disintegrates after about 20 seconds. The reaction is scored visually. The more gel formation, the higher the score.
  5. Rinse the CMT paddle after each test.

CMT Procedure Video


The table below describes the CMT scoring system. Each quarter is scored using the following scale. These scores correlate to an average SCC range for each quarter.

Table 12.1: CMT Scoring System

CMT Score


SCC Range

N (negative) No thickening of the mixture 0 – 200,000
T (trace) Slight thickening of the mixture. Trace reaction seems to disappear with the continued rotation of the paddle. 200,000 – 400,000
1 Distinct thickening of the mixture, but no tendency to form a gel. If the CMT paddle is rotated for more than 20 seconds, thickening may disappear. 400,000 – 1,200,000
2 Immediate thickening of the mixture, with a slight gel formation. As the mixture is swirled, it moves toward the center of the cup, exposing the bottom of the outer edge. When the motion stops, the mixture levels out and covers the bottom of the cup. 1,200,000 – 5,000,000
3 Gel is formed and the surface of the mixture becomes elevated (like a fried egg). The central peak remains projected even after the CMT paddle rotation is stopped. Over 5,000,000

 Knowledge check


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