IDF/ICAR Project Group on Reference System for Somatic Cell Counting

The IDF (International Dairy Federation) and ICAR (International Committee for Animal Recording) have launched a new project jointly, which intends to set up an international reference system for somatic cell counting in raw milk.


Global markets with expanding streams of exported/imported goods involve a focused attention on equivalence of analytical results. Indeed, analytical results play a major role in free and fair trade.
Apparently, independent local calibration cannot always fulfil the rising demands forworldwide equivalence of analytical results.
It occurs that worldwide equivalence of analytical results cannot be safeguarded by “solely” producing standardized analytical methods. In addition, with some parameters, standardized reference materials are lacking and the reference method shows limited performance.
Thus, sophisticated large scale reference systems are needed where traditional calibration schemes are lacking precision and effectiveness.


A reference system is a tool to provide a commonly acknowledged reference level for a given analytical parameter.
Joint recognition by regulatory bodies, competent authorities and other stakeholders is essential for an effective functioning. A more extensive explanation on the background and aims as well as on the elements of reference systems was published in the Bulletin of the IDF 427/2008.

A reference system is a systematically developed anchoring system that is fed by different types of information from various sources in a laboratory network structure:

  • Reference method (direct) results,
  • Routine method (indirect) results,
  • Proficiency testing.

Somatic Cell Counting is one of the most frequently performed tests worldwide, estimated at over 500.000.000 tests/year.

Somatic Cell Counting – as an indicator of udder health status – is relevant in food legislation, payment of raw milk, affect milk composition and quality, and also has amajor impact on farm management and breeding programs.

Reliable Somatic Cell Counting by reference method is a major challenge:

  • Reference method is a direct microscopic cell counting of stained cells. What to count and what not to count can be questioned. The reference method derives from old techniques, and is tedious, cumbersome and has poor performance;
  • The target analyte of routine methods is not commonly accepted as “reference” basis;
  • No certified reference material/“golden standard”;
  • Secondary reference materials have limited shelf life and batch homogeneity default during storage;
  • As a consequence, several routine laboratories have set up their own ‘reference system’ in order to anchor their counting level.
  • Obtaining a suitable reference material, representative and stable.
  • A laboratory database with a competence scoring system,
  • A calculation model for determining assigned values,
  • Exploring the existing solutions and linking them to test the concept of reference system in a pilot study,
  • Organizational matters,
  • Communication plan to promote the project near analytical-oriented stakeholders (laboratories, reference material providers), and other stakeholders (animal health bodies, authorities).
  • A reference system is a complement to the ‘traditional’ way of calibrating routine methods.
  • A harmonized worldwide reference system will safeguard the validity and equivalence of analytical results anywhere, anytime, anyhow.
  • Its implementation in the dairy sector will promote the acceptance and mutual confidence in analytical results, thereby helping free and fair trade.
  • Somatic cell counting is the best parameter to explore the feasibility of a worldwide reference system, because the SCC reference method has poor performance.
  • The potential benefit of its implementation will then be demonstrated for other parameters.
1 - What is the aim of the project?

When goods are moving, analytical results should be comparable and “equivalent”

  • Worldwide
  • In the long run
  • Between different methods
    The equivalence of analytical results should be reached at any place at any time;
  • A reference system is defined as an anchoring system fed by a network of laboratories. It will be a tool to improve and safeguard equivalence, where the traditional approach of calibrating with reference methods shows limited performance.
2 - What is the precision of the SCC reference method vs routine methods ?


3 - What does the traditional approach consist of and why is it limited?

Routine methods are traditionally calibrated by using a calibration set of reference materials which reference values have been determined by reference method.
In many cases, the precision of the reference method is not satisfactory and gives uncertainty to the reference value. In addition, when applied in only one laboratory, the reference method cannot guarantee a reliable enough reference value. The stability and homogeneity of reference materials (RM) is also a key to get reliable reference. For some parameters, equivalence is difficult to be achieved by straightforward analytical means or reference materials.

4 - Which routine methods for SCC in milk are concerned?

Somascope TM, Somacount TM, Bactocount TM, Nucleocounter TM, DCC Counter TM, Fossomatic TM, etc.

5 - How will a reference system for SCC in raw milk work? Will it replace our existing procedures of calibrating the routine methods?

The idea is to rely on existing calibrating systems, not to remove them. The reference system will be implemented thanks to contributing competent laboratories. They will feed a database with their results from reference method AND standardized routine methods. Data will be processed through a calculation model to be developed. This will create an international reference material with a worldwide recognized assigned value which will be used to anchor the national laboratories, the reference materials providers and the routine methods to a golden standard.