Frequently Asked Questions

Below you can find a collection FAQs on CalibrationCertificationConsumables, Homogenization, Maintenance, Mid-IR Analysis, Milk, Performance, Results, and Service.

If you do not find the answers to your questions, please do not hesitate to contact us at (for support issues) or (for any other questions).


There are two required quality control procedures of the Miris Human Milk Analyzer: the check procedure with zero-level adjustment, and a validation of the internal calibration with Miris Calibration Control Kit.

The check procedure must be performed at start-up and after cleaning the instrument if continuing analysing samples. By doing a check, and an adjust when this is indicated on the instrument screen, the validity of the internal calibration is ensured by control of, and if necessary adjustment to, the correct zero-level.

As a daily control of the internal calibration, analyse the two different standard solutions included in the Miris Calibration Control Kit: Miris Calibration Control 1 and Miris Calibration Control 2. 

The instrument regularly needs to be controlled by doing the check procedure with zero-level adjustment, and by validation of the internal calibration using the Miris Calibration Control Kit. As long as these two quality control procedures pass, the instrument performs as expected. Contact Miris ( or your local distributor if the internal calibration of your Miris Human Milk Analyzer returns values deviating from the established target values of the Miris Calibration Control Kit.   

The Miris Calibration Control Kit can be ordered from your local distributor or by contacting Miris (

In many cases yes, a message will appear on the display: ”No energy in the system” or ”Air in the system”. The effect of a bad sample may also be zero values, or very low measurement values 0.5-0.6 g/100ml, for protein.

The instrument is calibrated on a set of human milk samples with varying contents of fat, protein and carbohydrate. These are analysed with chemical standard methods validated for analysis of human milk and the results are used for calculating the internal calibration. The internal factory calibration of the Miris Human Milk Analyzer is optimized to measure human milk of normal biological variation.


Yes, according to the European Commission Directive 98/79/EC on in vitro diagnostic medical devices.


Syringes can be re-used as long as they fit tightly to the inlet. If a syringe is loose there is a risk that air bubbles enter the system, which will disturb the measurement. Be very careful with hygiene and always disinfect syringes that are re-used for milk analysis.

Approximately 5 ml of Miris Check is needed to zero-set an instrument.

15 ml cleaning solution is needed for each cleaning session. Miris Cleaner is also used to clean the filter (approx. 10 ml each time).

Diluted solutions of Miris Cleaner and Miris Check should be used within 3 months from opening.

Store the concentrate of Miris Cleaner and Miris Check dark, at room temperature (20-30°C), sealed in container in which it is supplied. Store the diluted solution dark and in glass or plastic containers.

Store unopened vials dark, at room temperature (20-30° C). Do not freeze.

Use opened vials directly. Do not store opened vials to re-use the content.


The required homogenizing effect is only known by the recommended devices. The Miris Human Milk Analyzer Calibration 1 is adapted to homogenisation by Miris Ultrasonic Processor, Miris Sonicator or VCX-130, these are high-intensity ultrasonic liquid processors, where ultrasonic waves will generate the homogenising effect by cavitation. This method is suitable for homogenising small sample volumes as required for the Miris Human Milk Analyzer. The Miris Ultrasonic Processor has a 3 mm probe and settings optimised for human milk (amplitude 75% full scale, no pulsation). The energy output is approximately 20 J/sec per ml of human milk.

Yes, when using the Miris Human Milk Analyzer Calibration 1 the milk must be homogenised to get correct results.


Yes, the following error messages exist:

"Air in the system". If this message appears the sample has not been properly injected. The cause may be a worn-out syringe, or a foamy sample. Repeat the measurement after injecting a new sample, and/or using a new syringe.

"No energy in the system". If this message appears the measurement cell is blocked. The cause may be an improper sample or a hardware error. Clean the system and repeat the measurement.

"Bad sample, check the inlet and try again”. Sample is not properly injected; cause may be a foamy sample, a worn-out syringe or worn-out rubber details in the in- and outlets. Repeat the measurement with a new sample, and/or new syringe. Replace rubber gaskets.

“Data limited has been reached. Dumping data, please wait”. Too much data saved in the data file, the instrument will erase the oldest data automatically. Wait a few minutes and the message will disappear. 

“Error”. Restart the instrument with the on/off switch.

“Transmission change”. The transmission has decreased more than 10% on one or several instrument filters (Tr1-Tr4). Click ‘ok’ on the message. Ensure the Miris Check solution is not contaminated and clean the system and repeat the check procedure.

“Warning, out-of range measurement on parameter…”. Measurement result is out-of-range, higher or lower than the instrument measuring range for a parameter. The measurement result cannot be regarded as with normal accuracy. Disregard the result. Let the sample stand in the water bath 40°C a while longer. Homogenise the sample. Ensure that any foam disintegrates before taking a sample for injection.

For more information see the Miris Human Milk Analyzer user manual or contact Miris ( or your local distributor.

Yes, there are different levels for log in; administrator, user or guest. It is also possible to create a user list (signature).

The log-in function is permanent (non-optional) in instruments running on software version 3.02 and later (optional, i.e. may not be present, in instruments with earlier versions).

Miris can only be of help setting up routines for proper use of the Miris Human Milk Analyzer. For other issues regarding milk handling etc. please consult the authorities in your country.

This is not a question for Miris AB – discuss with a dietician or ask the supplier of fortifier.

Because the injected sample volume will rinse out the previous sample.

After every 10th analysis or when you intend to leave the instrument more than 5 minutes.

No longer than 5 minutes without follow up with a new milk sample or Miris Cleaner.

Only if you are going to use the instrument on a daily basis.

The check procedure must be performed at start-up and after cleaning the instrument if continuing analysing samples (every 10th analysis).

Yes. Miris provides a printer and a special cable is required. If you purchase the printer from somewhere else, you have to buy the cable from Miris to be able to connect the printer to the instrument.

Yes. In the instrument menu “Analysis”, press ID. Each sample or sample batch can be given a unique ID (max 20 characters), which will stay the same until changed. Use the instrument’s keyboard, an external keyboard (USB) or a barcode reader. Avoid using commas (,) in ID’s, since this complicates the data interpretation in Microsoft Excel.

After installation and usage, and if the instrument is to be stored for a long period, always leave the instrument filled with distilled/deionised water and make sure the system is closed to avoid evaporation. Remember to inject 10 ml fresh distilled/deionised water, with the same temperature as the instrument has, every second week.

Mid-IR Analysis

Mid-IR is a physical method that measures the macronutrient (fat, protein, and carbohydrate) content of milk, through the absorption of energy of unique functional groups in the molecules of the macronutrients.

Ultrasound technology measures the speed of sound in milk depending on a density characterisation of fat, and estimates the fat content from this.  Contents of protein and carbohydrate are calculations based on the estimated fat content.

The instrument has different filters intended for a specific macronutrient (fat, protein, carbohydrate) and uses four different wavebands. The wavebands used are specific for the functional carbonyl groups (5.7µm) for fat determination; amide groups (6.5 µm) for protein determination; and hydroxyl groups (9.6 µm) for carbohydrate determination.

The Miris Human Milk Analyzer is based on mid-infrared (MIR) transmission spectroscopy. A thin fluid film of the milk sample is exposed to MIR radiation and the transmitted MIR energy is detected at specific wavebands within the infrared spectrum. The reduced transmissions at the different wavebands are proportional to the concentration of macronutrients (fat, protein, carbohydrate) in the sample.


Crude protein, also referred to as total protein, is the protein content based on the total amount of nitrogen (N) in a sample. This means that non-protein nitrogen (NPN) compounds will also be included in this value. True protein on the other hand represents only the content of actual protein (based on only protein N), hence the denotation true.

Human milk contains a large proportion of NPN, about 20-25 % of the total N. This is necessary to keep in mind when comparing results and reference samples analysed by different methods – does it give crude or true protein.

The Miris Human Milk Analyzer presents the crude protein value, and the true protein value by estimating 20% NPN.

Miris applies the factor 6.38 to convert N content to protein content.

Longer storage time increases the risk of protein aggregation, which may result in the Miris Human Milk Analyzer giving low protein values or zero/negative protein values. Long storage time also gives an increased risk for “oiling off” (oil droplets on the surface of the milk). When analysing such milk there is a high risk of unstable and inaccurate fat values.

The cuvette volume is very small, a few microliters. However, the whole system with inlet, tubes, and outlet, makes up for a larger volume.

The minimum recommended sample injection is 3 ml.  A carry-over effect <3% from previous sample is not guaranteed at smaller injection volumes.

In the following order:

  1. thaw the sample in a refrigerator (2-6 °C) or in a cold water bath (10-20 °C)
  2. heat the sample to 40 °C in a water bath (or in a Miris Heater)
  3. homogenise the sample with Miris Ultrasonic Processor (or equivalent device recommended by Miris)
  4. Analyse immediately or keep the sample in the water bath until analysis, maximum 15-20 minutes

Yes, there is. The standard operation procedure can be found in the Miris Human Milk Analyzer user manual.

The composition of human milk is highly variable, with factors such as diurnal variation, longitudinal changes associated with postpartum duration, time since last feed, volume of milk consumed at the prior feed, time during feed, and maternal physiological let down to consider.

For an introduction on this topic, see Chapter 11 in the Miris HMA User Manual.

There are three main reasons for pre-heating the milk:

1) In order to get a more homogeneous sample by making the milk fat liquid, which gives more reliable results.

2) Cuvette temperature, i.e. analysis temperature, is 40 °C.

3) To avoid (permanently) damaging the cuvette.

Mix gently by turning the bottle back and forth or in a swirling motion. Keep in mind that this might be a non-representative sample when performing the analysis – the Miris Human Milk Analyzer measures only the milk injected into the cuvette.

If the milk has started to curdle and separate, if there are visible white spots on the walls of the sample container, or if there are oil droplets on the surface (oiling-off). When any of these items are noticed then the sample should not be analysed by the Miris Human Milk Analyzer.

Milk preserved by ”Bronopol” 2-bromo-2-nitropropane-1,3-diol is OK to analyse by the Miris Human Milk Analyzer.

In human milk the proportion of carbohydrates is about 70 % lactose and 30 % oligosaccharides. In the Miris Human Milk Analyzer the determination is based on the hydroxyl groups of carbohydrates, which means it measures the total carbohydrate content.


A low coefficient of variation (CV = SD / mean) implies good accuracy. Always compare the variation in accuracy vs. the variation of the measured population.

Accuracy is a measure of how well an indirect method (such as the Mid-IR) is compared to a reference method (or against the “true value”). Analytical accuracy can be specified with standard statistical measurements. Two different examples: 

Differential Method
Calculation of the difference between Miris Human Milk Analyzer and the reference method. D = x – y 
Mean value of the differences, D = ƩD / n 
Standard deviation (SD) of the differences (D = x – y) Miris Human Milk Analyzer (y) and reference (x) 
SD = Ʃ(D2 – (ƩD/n)2) / n – 1

Regression Method
Yi = a + bXi + ei 
Yi = dependent variable (reference method) 
a = intercept (or bias) 
b = slope 
Xi = independent variable (Miris Human Milk Analyzer) 
ei = variance of linearity (accuracy)

The intra-assay variation can be calculated in different ways. It is similar to precision or repeatability. Double measurements of n different samples gives the possibility to calculate the within variation using an analysis of variance (ANOVA) model. 

Between samples  
Within samples  

The estimated within variation gives the methods intra-assay variation (precision, repeatability). These statistical models will be found in most statistical books. You can also calculate the intra-assay variation by calculating the variance of difference between measurement 1 and 2. In ISO 8196-1:2000 a simplified equation is given how to calculate the standard deviation of the difference between double measurements of different samples.

Milk is not a true solution, it is an emulsion (a mixture of liquids that normally does not mix easily, such as water and oil). It is not homogenous by nature and therefore every small sample drawn from a bottle will differ a little bit. There is a normal variation in the analysis as there are a lot of factors that affect the result (both Mid-IR instrument factors, handling factors, and sample factors).

See Chapter Performance Characteristics in the Miris HMA User Manual.

Miris declares the following measurement performance:

By using the required quality control procedures, the check function and the instrument validation procedure, correct functionality of the instrument is ensured.


Results are displayed in the menu under “result – viewer”. The results can be printed directly with a printer that can be ordered from Miris or your local distributor. The results are also available in .txt file format, press ‘Transfer’ to export the results file to a USB flash drive attached to the instrument. The result file can be exported to Microsoft Excel (for instruction see the Miris Human Milk Analyzer user manual).

Perform duplicate analyses. If there is a large deviation between duplicates of the same sample, do a third analysis in order to detect and exclude incorrect results. Make notes of sample, its origin, sampling procedure etc. Validate the internal calibration of the Miris Human Milk Analyzer with the Miris Calibration Control Kit.


Make sure to keep the instrument clean, and pay special attention to the in- and outlets. The inlet should be disassembled and cleaned once a week or every 100th analysis, whichever comes first.

Replace filters and O-rings in the in- and outlet if they look worn, or approximately once a year.

Control the displayed “Change %”-line after performing a ‘CHECK’ and rinse the instrument thoroughly with Miris Cleaner if the percentage is getting close to ±10%.

Miris recommends yearly maintenance service of the instrument. Contact Miris at for more information.

Polish the tip (the flat end) of the probe with an emery cloth after each use. Make sure to polish the probe evenly, avoiding bevelled edges, and to complete­ly remove any milk residues.

The probe will eventually be worn and then it needs to be replaced. Contact if this is something you suspect.

Service can only be performed by an authorised service technician. Ask your local distributor or contact Miris (