Many laboratories believe that their role is only to issue reports and that their responsibility to the client ends at that point. These laboratories either lack the technical skill to assist clients or have a policy that result interpretation is not provided.
The roots of Biotech Laboratories were firmly grounded in medical microbiology within the field of pathology services. Can you imagine if a pathology laboratory sent your doctor the report of your blood tests with over 30 individual analyses and didn’t highlight those tests that were abnormal? It would take hours to look up the acceptable limits. It just doesn’t happen. We see our role in very much the same way. Our policy is to never recommend a client have an analysis performed unless we can assist them with interpretation of the result, either verbally or preferably on the laboratory report.
How can a laboratory recommend that you perform a set of analyses without telling you how to interpret each result? At the very least all laboratories should be able to direct you to a standard or guideline document that specifies the analyses and their respective acceptable values for every test they recommend.
The advantage of having an indication of acceptability against each analysis is obvious. It means that reports can be screened by many levels of staff and do not rely on the presence of QA officers or external consultants.
Interpretive reporting is based on the sample classification. Against each sample category the acceptable limit is listed for the different analyses. At present we have over 150 different sample categories in our computer system. These include Australian and International standards and guidelines and also specified acceptable limits that are provided by clients. The reference for the result interpretation is detailed on the base of the report. Where clients request analyses that have no acceptable limits, the results appear without interpretation.
To be able to issue NATA endorsed reports with interpretations we are required to not only list the measurement of uncertainty (MU) range on the report, but also evaluate the range when determining if the result is acceptable. Remember that the MU range represents the true numeric result and can be best explained by stating that if we took a sample and tested it 100 times, 95 times out of a 100 the result would fall somewhere between the lower and upper MU range values. For further information on MU - click link. On all reports any result value or MU range value that is above the acceptable limit will appear in red text.
For example: The acceptable result for Faecal Coliforms in a water sample which is classified as “Irrigation - Used for Pasture and Fodder for dairy animals (With withholding period of 5 days)” the acceptable limit is <1,000 cfu/mL.
Looking at different result values and how they will appear on the report
Example A. Passing Result
Result: Faecal Coliforms: <100 cfu/100mL
ü Faecal Coliforms <100 CFU/100mL AL: <1,000
The result is a pass which is shown by the ‘ü’ at the start of the result line. Where there is not a definitive numeric value a MU range cannot be calculated and does not appear for the result. It is a pass because the result of <100 is below the acceptable limit (AL).
Example B. Failing Result
Result: Faecal Coliforms: 2,400 cfu/100mL
X Faecal Coliforms 2,400 (MU: 1,400 to 4,100) CFU/100mL AL: <1,000
The result is a fail which is shown by the ‘X’ at the start of the result line. It is a fail, not because the result of 2,400 is above the acceptable limit (AL) but because the lower limit of the MU range (1,400) is above the acceptable limit.
Example C. Passing Result
Result: Faecal Coliforms: 600 cfu/100mL
ü Faecal Coliforms 600 (MU: 290 to 850) CFU/100mL AL: <1,000
The result is a pass which is shown by the ‘ü’ at the start of the result line. It is a pass, not because the result of 600 is below the acceptable limit (AL) but because the upper limit of the MU range (850) is below the acceptable limit.
Example D. Uninterpretable Result
Result: Faecal Coliforms: 800 cfu/100mL
Faecal Coliforms 800 (MU: 470 to 1,400) CFU/100mL AL: <1,000
The result cannot be interpreted as shown by neither ü nor a ‘X’ at the start of the result line. It cannot be interpreted as although the result of 800 is below the acceptable limit (AL) the upper limit of the MU range (1,400) is above the acceptable limit.
Example E. Uninterpretable Result
Result: Faecal Coliforms: 1,100 cfu/100mL
Faecal Coliforms 1,100 (MU: 650 to 1,900) CFU/100mL AL: <1,000
The result cannot be interpreted as shown by neither ü nor a ‘X’ at the start of the result line. It cannot be interpreted as although the result of 1,100 is above the acceptable limit (AL) the lower limit of the MU range (650) is below the acceptable limit.
In these last two examples it is up to the client to decide on how they will evaluate the result. Although it should be stated that it is more likely that the true result is acceptable in Example D rather than Example E.
Example F. Failing Result
Result: Faecal Coliforms: >100,00 cfu/100mL
X Faecal Coliforms >100,000 CFU/100mL AL: <1,000
The result is a fail which is shown by the ‘X’ at the start of the result line. Where there is not a definitive numeric value a MU range cannot be calculated and does not appear for the result. It is a fail because the result of >100,000 is above the acceptable limit (AL).
There are two documents from Food Standards Australia New Zealand (FSANZ) that reference the microbiological limits for food. These being:
- Schedule 27 Microbiological limits for foods (Schedule 27)
- Compendium of Microbiological Criteria for Food (Compendium)
Most ready to eat foods are not specifically classified in Schedule 27. In the Compendium, it does not only list “satisfactory” limits, but it also lists other limits for “marginal”, “unsatisfactory” and “potentially hazardous”. The meaning and remedial action required for when results of food testing falls into these categories is detailed in the Compendium.
The spoilage analysis of a Standard Plate Count (Plate Count) and the indicator bacteria of E. coli and Enterobacteriaceae have limits for “satisfactory”, “marginal” and “unsatisfactory”. No result for any of these analyses will result in a classification of “potentially hazardous”.
The pathogens fall into two groups. One group where a numeric count is obtained such as Clostridium perfringens and coagulase positive staphylococci and the other where it is a presence absence test such as Salmonella and Campylobacter. For the group where a count is performed the Compendium has limits for “satisfactory”, “marginal”, “unsatisfactory” and “potentially hazardous”. For the presence absence group there are only two limits, “satisfactory” and “potentially hazardous”.
Biotech Laboratories has now been able to further develop our reporting program so that the result will be categorised based on the actual numerical result when the result is a fail based on the lower measurement of uncertainty range. The explanation of the determination of a pass or failing result can be found here.
An example of this reporting format can be seen by clicking this link.