prEN ISO 13366-2

• Abstract:

  This document gives guidance on the operating conditions for counting the total number of somatic cells, in both raw and chemically preserved milk, using flow cytometers.; The guidance is applicable to the counting of somatic cells in raw cow milk. The guidance is also applicable to raw milk of other species, such as goat, sheep and buffalo, if the specified prerequisites are met.

• Status: Not Published
• Publication Date: 05-Dec-2027
• ICS: 67.100.10 - Milk and processed milk products
• Technical Committee: CEN/TC 302 - Milk and milk products - Methods of sampling and analysis
• Current Stage: 4060 - Closure of enquiry - Enquiry
• Start Date: 07-Sep-2026
• Completion Date: 07-Sep-2026
• Ref Project: oSIST prEN ISO 13366-2:2026 - Milk - Enumeration of somatic cells - Part 2: Flow cytometry method (ISO/DIS 13366-2:2026)

• Revises: EN ISO 13366-2:2006 - Milk - Enumeration of somatic cells - Part 2: Guidance on the operation of fluoro-opto-electronic counters (ISO 13366-2:2006)
• Effective Date: 14-May-2025
• Revises: EN ISO 13366-2:2006/AC:2007 - Milk - Enumeration of somatic cells - Part 2: Guidance on the operation of fluoro-opto-electronic counters (ISO 13366-2:2006)
• Effective Date: 14-May-2025

prEN ISO 13366-2 is a CEN draft standard for enumerating somatic cells in milk by the flow cytometry method. It gives guidance on the operating conditions for counting total somatic cells in raw milk and chemically preserved milk, and it is intended for laboratories and dairy operators that need routine somatic cell counts, calibration, and quality control. The guidance applies directly to raw cow milk and also to raw goat, sheep and buffalo milk when the stated prerequisites are met.

What does prEN ISO 13366-2 specify?

prEN ISO 13366-2 specifies how to run flow cytometer-based counting of total somatic cells in milk, with attention to sample handling, calibration, routine checks, precision, and reporting. Sampling itself is outside the method and the document points users to ISO 707 | IDF 50 for sampling guidance.

The document is organized into clauses on scope, normative references, terms and definitions, principle, factors affecting results, calibration, sampling, determination, routine performance checks, species-specific remarks, precision, and test report. It also includes one informative annex.

Annex	What it covers
Annex A	Direct labelling (DNA stain) for total cell counting in milk using flow cytometry, including a non-dedicated flow cytometer approach

What are the key requirements of prEN ISO 13366-2?

Clause 4 sets out the measurement principle: the milk sample is mixed with buffer and stain, then passed through the counting section of a flow cytometer where stained particles generate electrical pulses that are processed into a cell count. In practice, this means the result depends on correct reagent dosing, mixing, optical detection, and signal discrimination.

Clause 5 focuses on everything that can change the count before analysis. The sample bottle should be suitable for transport, samples should be cooled promptly, freezing should be avoided, and chemical preservation should only be used with validated preservatives and colour tracers. For the reader, this means the pre-analytical chain is part of the method - poor handling can lower the count or distort the signal.

Clause 5 also distinguishes between sample types and practical risks. Bulk milk needs thorough mixing because cells can concentrate in the upper layer, while milk from individual animals should be representative of the whole milking when the aim is a whole-milking count. Problem samples such as clotted, dirty, high-erythrocyte, colostrum, late lactation or sour milk may require special care or avoidance.

Clause 6 covers calibration and reference materials. Reference materials should be produced under a quality system meeting ISO 17034, and the document recognizes certified reference material (CRM), secondary reference material (SRM), and in-house reference material (IRM). Calibration may be built from prepared milk samples made by adding leucocyte suspension, microfiltration, or centrifugation, and the calibration should cover the relevant counting range.

Clause 6 also requires a linearity check and regular calibration verification. The instrument should be checked for linear response in the working range, and the calibration should be checked at least monthly. In practice, a laboratory should not assume that one calibration is permanent - it needs ongoing confirmation that the instrument still tracks the reference values correctly.

Clause 9 defines the routine quality checks that keep the method under control. It covers blank checks, carry-over checks, pilot checks, repeatability, intralaboratory reproducibility, and external comparisons through proficiency testing. These checks matter because they reveal contamination, sample-to-sample influence, drift, and day-to-day stability problems before they affect reported milk results.

Clause 10 gives species-specific remarks. Goat milk, sheep milk and buffalo milk may need special attention because cell size, fat, protein, or background signals can differ from cow milk. The document allows cow-milk calibration to be used for goat and sheep milk on some instruments when the relevant range is covered, but only if the instrument response remains suitable for that milk type.

Clause 11 provides precision information for repeatability, intralaboratory reproducibility, and reproducibility. The values are presented for cow milk, with a note that other species may be less favourable. For buyers and laboratories, this section is useful when setting acceptance criteria, comparing instruments, or judging whether a result is consistent.

Clause 12 states what the test report should contain. A report should identify the sample, note the sampling method if known, give the sampling date and sample type, identify the method used, record any operating details that may have influenced the result, and state the result in thousands of cells per millilitre or the final quoted result after repeatability checking.

What terms does prEN ISO 13366-2 define?

• reference method - the somatic cell counting method described in ISO 13366-1 | IDF 148-1, used as the benchmark for comparison and traceability.
• somatic cells - cells that give fluorescence above the defined threshold after DNA staining in their nuclei, with the count expressed in cells per millilitre.
• certified reference material (CRM) - a reference material with certified values used to anchor calibration and traceability.
• secondary reference material (SRM) - a reference material prepared by an external supplier and traceable to CRMs.
• in-house reference material (IRM) - a laboratory-prepared reference material whose traceability is maintained through CRMs or SRMs.
• direct total somatic cell counts (dSCC) - the alternative method in Annex A that uses direct DNA staining and a non-dedicated flow cytometer.

Who uses prEN ISO 13366-2?

prEN ISO 13366-2 is used by dairy laboratories, milk-testing laboratories, and quality teams that measure somatic cell counts in routine milk analysis. It is also relevant to milk producers, processors, and buyers who depend on SCC results for raw milk monitoring, acceptance decisions, and quality control.

Instrument operators use it to set up flow cytometers, prepare samples, and run blanks, pilot samples, and repeatability checks. Calibration and reference material suppliers, as well as proficiency testing providers, also use it because the document ties the method to CRM/SRM/IRM traceability and interlaboratory comparison.

What changed in prEN ISO 13366-2 from the previous edition?

This third edition replaces the second edition ISO 13366-2 | IDF 148-2:2006 and is technically revised. The foreword states these main changes:

• the outdated rotating disk technique has been deleted;
• guidance has been added on building a robust metrological system, including use of a certified reference material (CRM) and assignment of values to secondary reference material;
• control of the ratio/reagent has been removed;
• Annex A adds a method for total somatic cell counts (dSCC) in milk using a non-dedicated flow cytometer and commercially available non-proprietary chemicals.

Which standards are used with prEN ISO 13366-2?

Reference	What it contributes
ISO 8196-1	Analytical attributes for alternative milk analysis methods and overall accuracy concepts
ISO 8196-2	Calibration and quality control in the dairy laboratory, including control charts and calibration practice
ISO 8196-3	Protocol for evaluating and validating alternative quantitative methods, including intralaboratory reproducibility
ISO 13366-1	The microscopic reference method for somatic cell counting and the basis for traceable reference values
ISO 17034	Competence requirements for producers of reference materials
ISO/IEC 17043:2023	Requirements for proficiency testing providers used in external comparisons
ISO 707	Guidance on sampling, which Clause 7 points to for sample collection practice
IDF 128-1, IDF 128-2, IDF 128-3, IDF 148-1	IDF counterparts of the ISO milk-analysis standards used alongside the method

What does the prEN ISO 13366-2 document contain?

The document contains clause-level guidance for running somatic cell counts by flow cytometry, including the factors that affect results, calibration routes, routine control checks, species-specific remarks, and reporting rules. It also includes tables for calibration ranges and precision, plus formulas for carry-over and linearity evaluation.

Annex A adds a worked alternative approach for direct labelling with a DNA stain. That annex describes the sample-preparation sequence, instrument settings, reagents, gating approach, calculation of results, and a preliminary precision comparison, which makes it useful for method development or instrument adaptation.

SLOVENSKI STANDARD
01-september-2026
Mleko - Ugotavljanje števila somatskih celic - 2. del: Metoda pretočne citometrije
(ISO/DIS 13366-2:2026)
Milk - Enumeration of somatic cells - Part 2: Flow cytometry method (ISO/DIS 13366-
2:2026)
Milch - Zählung somatischer Zellen - Teil 2: Leitfaden zum Betrieb
fluoreszenzoptoelektronischer Zählgeräte (ISO/DIS 13366-2:2026)
Lait - Dénombrement des cellules somatiques - Partie 2: Méthode de cytométrie en flux
(ISO/DIS 13366-2:2026)
Ta slovenski standard je istoveten z: prEN ISO 13366-2
ICS:
67.100.10 Mleko in predelani mlečni Milk and processed milk
proizvodi products
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 13366-2
IDF 148-2
ISO/TC 34/SC 5
Milk — Enumeration of somatic
Secretariat: NEN
cells —
Voting begins on:
Part 2:
Flow cytometry method
Voting terminates on:
ICS: 67.100.10
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Reference numbers
ISO/DIS 13366-2:2026(en)
IDF 148-2:2026(en)
ISO/DIS 13366-2:2026(en)
IDF 148-2:2026(en)
© ISO and IDF 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office International Dairy Federation
CP 401 • Ch. de Blandonnet 8 Silver Building • Bd Auguste Reyers 70/B
CH-1214 Vernier, Geneva B-1030 Brussels
Phone: [phone] Phone: [phone]
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Website: www.iso.org Website: www.fil-idf.org
Published in Switzerland
ii
ISO/DIS 13366-2:2026(en)
IDF 148-2:2026(en)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Factors affecting the results of measurements. 2
5.1 Sample bottles . .2
5.2 Sampling .2
5.2.1 General .2
5.2.2 Bulk milk samples .2
5.2.3 Milk samples from individual animals .2
5.3 Preservation .3
5.4 Sample storage and transport .3
5.5 Interfering substances . .3
5.6 Sample quality at analysis .4
5.7 Chemicals .4
5.8 Instrument condition . .4
6 Calibration . 4
6.1 Reference materials .4
6.1.1 General .4
6.1.2 Preparation of calibration samples .5
6.1.3 Assignment of reference values .5
6.1.4 Storage conditions and keeping time .5
6.2 Calibration procedure .6
6.2.1 Calibration . . .6
6.2.2 Check on linearity .6
7 Sampling . 7
8 Determination . 7
9 Checks on performance in routine operation . 7
9.1 Blank checks .7
9.2 Carry-over effect .7
9.3 Pilot checks .8
9.3.1 General .8
9.3.2 Pilot milk .8
9.3.3 Assignment of pilot milk values .8
9.3.4 Use of pilot milk samples .8
9.4 Additional instrument surveillance .9
9.5 Repeatability .9
9.6 Intralaboratory reproducibility .9
9.7 External comparisons .9
10 Specific remarks for the use with milk from different species . 9
10.1 General .9
10.2 Cow milk .10
10.3 Goat milk .10
10.4 Sheep milk .10
10.5 Buffalo milk .10
11 Precision . 10
11.1 Repeatability .10
11.2 Intralaboratory reproducibility .11
11.3 Reproducibility .11

iii
ISO/DIS 13366-2:2026(en)
IDF 148-2:2026(en)
12 Test report .12
Annex A (informative) Direct labelling (DNA stain) for the total cell counting in milk using flow
cytometry in milk .13
Bibliography .18

iv
ISO/DIS 13366-2:2026(en)
IDF 148-2:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO’s adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 5,
Milk and milk products, and the International Dairy Federation (IDF), in collaboration with the European
Committee for Standardization (CEN) Technical Committee CEN/TC 302, Milk and milk products – Methods
of sampling and analysis, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement). It is being published jointly by ISO and IDF.
This third edition cancels and replaces the second edition (ISO 13366-2 | IDF 148-2:2006), which has been
technically revised.
The main changes are as follows:
— Outdated method has been deleted as rotating disk technique;
— Indications to build a robust metrological system as the use of a certified reference material (CRM) and
the procedure to assign the value to the secondary reference material;
— The control of ratio/reagent has been eliminated;
— Addition of method for total somatic cell counts (dSCC) in milk, using a non-dedicated flow cytometer
and commercially available non-proprietary chemicals as Annex.
A list of all parts in the ISO 13366 | IDF 148 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
IDF (the International Dairy Federation) is a non-profit private sector organization representing the
interests of various stakeholders in dairying at the global level. IDF members are organized in National
Committees, which are national associations composed of representatives of dairy-related national interest
groups including dairy farmers, dairy processing industry, dairy suppliers, academics and governments/
food control authorities.
v
ISO/DIS 13366-2:2026(en)
IDF 148-2:2026(en)
ISO and IDF collaborate closely on all matters of standardization relating to methods of analysis and
sampling for milk and milk products. Since 2001, ISO and IDF jointly publish their International Standards
using the logos and reference numbers of both organizations.
IDF draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IDF takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, IDF had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. IDF shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
This document was prepared by the IDF Standing Committee on Laboratory Statistics and Quality Assurance
and ISO Technical Committee ISO/TC 34, Food products, Subcommittee SC 5, Milk and milk products. It is
being published jointly by ISO and IDF.
The work was carried out by the IDF/ISO Action Team S18 of the Standing Committee on Laboratory Statistics
and Quality Assurance under the aegis of its project leaders Mrs S. Orlandini (IT) and Mr P. Trossat (FR).

vi
ISO/DIS 13366-2:2026(en)
DRAFT International Standard
IDF 148-2:2026(en)
Milk — Enumeration of somatic cells —
Part 2:
Flow cytometry method
1 Scope
This document gives guidance on the operating conditions for counting the total number of somatic cells, in
both raw and chemically preserved milk, using flow cytometers.
The guidance is applicable to the counting of total somatic cells in raw cow milk. The guidance is also
applicable to raw milk of other species, such as goat, sheep and buffalo, if the specified prerequisites are met.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 8196-1, | IDF 128-1, Milk — Definition and evaluation of the overall accuracy of alternative methods of milk
analysis — Part 1: Analytical attributes of alternative methods
ISO 8196-2, | IDF 128-2, Milk — Definition and evaluation of the overall accuracy of alternative methods of milk
analysis — Part 2: Calibration and quality control in the dairy laboratory
ISO 13366-1, | IDF 148-1, Milk — Enumeration of somatic cells — Part 1: Microscopic method (Reference method)
ISO 17034, General requirements for the competence of reference material producers
ISO/IEC 17043:2023, Conformity assessment — General requirements for the competence of proficiency testing
providers
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
reference method
method described in ISO 13366-1 | IDF 148-1 for the counting of somatic cells
3.2
somatic cells
those cells that show more than a threshold intensity of fluorescence due to the staining of DNA in their
nuclei
Note 1 to entry: The number of somatic cells is expressed in cells per millilitre.

ISO/DIS 13366-2:2026(en)
IDF 148-2:2026(en)
4 Principle
Flow cytometers designed for automatically counting the total number of somatic cells in milk have functions
for the uptake of reagents and test sample, a mixing section and a counting section. In the mixing section,
the test sample is mixed with a buffer and a stain solution. Part of the resulting mixture is transferred to the
counting section.
For other flow cytometers, the steps described above can follow the procedure described in (see Annex A).
In the mixing section, closely controlled volumes of test sample and buffer/stain solutions are dosed and
mixed. Mixing can take place in a cup, a mixing chamber, or in the tubing leading to a flow cell.
In the counting section, part of the mixture is placed in the high-speed flow of a surrounding sheath liquid
in a capillary flow cell. Through acceleration, the mixture forms a thin string in which the somatic cells are
dynamically focused and aligned. This string then passes the objective of a fluorescence microscope.
Each stained particle produces an electrical pulse that is filtered, amplified and recorded. The resulting pulse
height distribution is electronically processed, whereby discrimination is made between noise signals and
pulses that are attributed to stained somatic cells. The discriminator level can either be fixed or dynamic.
Some instruments contain two channels in the counting section. In terms of analytical quality assurance,
such a situation should be considered equivalent to working with two separate units, so the performance
should be evaluated separately for each channel.
5 Factors affecting the results of measurements
5.1 Sample bottles
Sample bottles should be fit for use; i.e. to transfer test samples from the point of sampling to the laboratory
without loss or damage.
Care is to be exercised that sample bottles are leak-proof and that a proper empty volume is left. Too large an
empty volume can facilitate churning; too small an empty volume can cause problems with mixing.
5.2 Sampling
5.2.1 General
Sampling materials (i.e. sample bottles, beakers and sampling devices) should be clean and dry. Where
automatic samplers are used, these should have been properly validated.
Test samples should preferably be cooled immediately after sampling at 4 °C ± 2 °C and be kept at that
temperature until counting (see 5.4) rather than being preserved. Freezing should be avoided. If preservation
is necessary, suitable means for chemical preservation of test samples are described in 5.3.
5.2.2 Bulk milk samples
Thorough mixing of the raw bulk milk to be sampled is essential. Somatic cells will concentrate in the upper
layer in the case of insufficient stirring.
5.2.3 Milk samples from individual animals
The release of somatic cells in the milk during milking is uneven. When the aim is to produce a representative
counting result for a whole milking, it is essential that a representative sample of the whole milking is
obtained. For diagnostic purposes, a sample of a partial milking may suffice.

ISO/DIS 13366-2:2026(en)
IDF 148-2:2026(en)
5.3 Preservation
If chemical preservation is considered necessary, the test sample (5.2.1) should be preserved as soon
as possible, but in any case within 24 h after sampling. In all cases, the test sample should be kept cool
(4 °C ± 2 °C) until the addition of the preservative.
WARNING — Sodium azide and potassium dichromate are highly hazardous reagents. Handle with
extreme care. Prepare and use the reagents only in a properly equipped laboratory, in a fume hood,
and always wear appropriate personal protective equipment (PPE), including gloves, lab coat an eye
protection.
Suitable preservatives are the following.
a) Boric acid: its final concentration in the test sample should not exceed 0,6 g/100 ml. Such preserved
samples may be stored at between 6 °C and 12 °C for up to a further 24 h.
b) Sodium azide: its final concentration in the test sample should not exceed 0,024 g/100 ml. Such preserved
samples may be stored at between 2 °C and 10 °C for up to a further 72 h.
c) Bronopol (2-bromo-2-nitro-1,3-propanediol): its final concentration in the test sample should not exceed
0,05 g/100 ml. Such preserved samples may be stored at between 2 °C and 12 °C for up to a further 6 d.
d) Potassium dichromate: its final concentration in the test sample should not exceed 0,2 g/100 ml. Such
preserved samples may be stored at between 2 °C and 12 °C for up to a further 6 d.
Accompanying colour tracers found to be suitable are:
— Patent Blue V with a final concentration in the test sample of up to 0,15 mg/100 ml;
— Yellow Orange S (E110) with a final concentration in the test sample of up to 1 mg/100 ml;
— a mixture of Patent Blue V and Eosin B with a final concentration in the test sample of up to 0,03 mg/100 ml
and 0,45 mg/100 ml, respectively;
— Methylene blue with a final concentration in the test sample of up to 0,5 mg/100 ml.
Other preservatives and colour tracers may be used provided that their effectiveness and conditions for use
have been soundly validated.
In all cases, properly validate the absence of interference for the counting equipment concerned before
application.
In cases where flow cytometers are combined with milk analysers for the measurement of other test
sample components, care should be taken that the applied preservatives and colour tracers do not affect the
counting result.
5.4 Sample storage and transport
Unpreserved test samples should be stored at 4 °C ± 2 °C and should be counted within 96 h after the
completion of sampling. Avoid freezing the test samples. Storage at higher temperatures and/or over longer
time scales may result in considerable loss of countable cells and therefore non-representative values. The
measurement of samples after freezing and thawing may result in lower counts (by 10 % to 20 %). The age
of the samples at freezing and the type of thawing process can influence the counting result.
5.5 Interfering substances
The use of substances that interfere in the counting should be avoided. Substances known to influence the
instrument read-out are preservatives and colour tracers at higher concentrations than specified 5.3.

ISO/DIS 13366-2:2026(en)
IDF 148-2:2026(en)
5.6 Sample quality at analysis
Breakdown of somatic cells (lysis) will result in an increase of smaller cell fragments. The lower intensity of
fluorescence after staining of these particles causes a shift in the pulse height distribution to the left. This
will hamper proper differentiation from noise pulses and therefore result in a lower count.
NOTE In several types of instruments, features are available for evaluating the position and the shape of the pulse
height distribution. See the relevant instructions and guidance from the instrument manufacturer.
After the processing of problematic samples, the flow path should be checked and possible cleaned. The
proper functioning of the instrument should be tested before further use. Possible problematic test samples
are
a) milk samples from severely infected udders, i.e. with clots;
b) milk samples with impurities;
c) milk samples with high numbers of erythrocytes;
d) colostrum;
e) late lactation milk;
f) sour milk.
Where possible, analysis of problematic test samples should be avoided.
5.7 Chemicals
All reagents used should be of recognized analytical and bacteriological quality. Water used should be
demineralized (remaining conductivity < 10 µS/cm) or water of at least equivalent purity. Manufacturer's
instructions for the preparation of the working solutions, the maximum storage time and storage
requirements should be followed.
Local conditions regarding the use and discharge of applied chemicals and effluents should be observed.
5.8 Instrument condition
5.8.1 General points of attention are:
a) the functioning of the mixing device and the stirrer,
b) possible disturbances at sample intake and in the flow system due to blocking by impurities, clots or
...