Originally published in CAP TODAY
Stephen J. Sarewitz, MD
From the files of the CAP’s checklist-related questions. Answers reviewed by Stephen J. Sarewitz, MD, chair of the Checklists Committee and staff pathologist, Valley Medical Center, Renton, Wash.
Q. Does microbiology checklist question MIC.21620 apply to immunologic tests only or to other tests conducted in the microbiology laboratory as well? We are performing quality control on all of our tests, so I don’t understand why this is needed.
A. The chances of a problem occurring with any test system increases when a change to the system requires the laboratory to check new reagent lots. Microbiology checklist question MIC.21620 applies to more than immunology testing. It is listed in the general microbiology section of the checklist and applies to all of microbiology. MIC.21620, phase II, reads:
Are new reagent lots and/or shipments checked against old reagent lots or with suitable reference material before or concurrently with being placed in service?
Note: For reagents used in qualitative testing of patient specimens, minimum cross-checking includes testing at least one known positive and one known negative sample with the new reagent lot or shipment. It is often preferable to do these validations with patient samples that have been tested previously or can be tested simultaneously with the old reagent lot. Good clinical laboratory science includes patient-based comparisons in many situations since it is patient results that are “controlled.” However, comparison with the old reagent lot is neither practical nor preferred in all cases, as in the case of a direct test for Shigella in stool, where the specimen is unstable and positives are infrequent. Another example where comparison with an old reagent lot may not be preferred would be when most patient specimens or the organisms derived from such specimens react very strongly in the test of interest. In this case, it might be preferable to use a well-characterized, weakly positive control to validate sensitivity of the new lot of reagents.
For reagents used to detect or evaluate cultured microorganisms, suitable reference material may consist of control strains of organisms or previously identified organisms.
Patient samples are ideal for checking new reagent lots for tests in which patient specimens can be frozen and used as external controls. For example, positive stool specimens for rotavirus testing, nasal washings for influenza or respiratory synctial virus, and serum for tularemia antibodies could be frozen and used with new lots or shipments. It is not practical to use patient specimens for lot-to-lot comparison of Strep A and Strep B kits since these tests use swabs. It is acceptable to use the external QC material from the previous kit on the new kit.
For those microbiology tests that use colonies—for example, coagulase, indol, and oxidase—the reagents should be tested using control strains of organisms or suitable reference material. Quality control should always be based on what would most closely mimic the testing you are performing for patient results.
Q. Are we required to purchase commercial quality control materials for such manual testing as sedimentation rates, manual body fluid cell counts, urine microscopy, and manual reticulocytes?
A. There is no specific checklist requirement regarding purchasing quality control material for manual testing. Proper training in technique, competency assessment, and proficiency testing are the best tools for assessing the accuracy and reliability of these tests. Maintaining files of unusual slides, reference materials, and atlases are also good approaches. One can also assess manual microscopic accuracy through competency, by comparing consistency of morphologic observations, and by correlating microscopic sediment findings with macroscopic results.
Hematology checklist item HEM.35566 and urinalysis checklist items URN.30800 and URN. 30850 address quality control:
- HEM.35566, phase II: Does the laboratory have a documented system to ensure consistency of morphologic observations among all personnel performing body fluid cell differentials?
Note: The section of the laboratory performing body fluid cell differentials must have a documented system that ensures that all personnel report microscopic morphologic data on patient samples in a similar fashion. For serial samples from the same patient, the laboratory must be able to document that all of its staff are consistent with respect to morphologic classification. Suggested methods to accomplish this include:
URN.30800, phase II: Does the urinalysis section of the laboratory have a defined, documented system to ensure consistency of morphologic observations among all personnel performing urine sediment microscopy?
Note: Suggested methods to accomplish this include:
- Circulation of body fluid smears with defined nucleated cell differential distributions, and/or
- Multi-headed microscopy, and/or
- Use of body fluid photomicrographs with referee and consensus identifications (e.g., former CAP Surveys photomicrographs)
URN.30850, phase II: Is there a documented procedure for correlation of microscopic sediment findings (such as casts, RBC, or WBC) with macroscopic results (presence of protein, positive occult blood, positive leukocyte esterase, etc.)?
- Circulation of preserved urine sediments with defined abnormalities involving leukocytes, erythrocytes, casts, bacteria, yeast, etc.
- Multi headed microscopy
- Use of urine sediment photomicrographs with referee and consensus identifications (e.g., former CAP Surveys clinical microscopy photomicrographs)
Refer also to the hematology and urinalysis checklist sections titled “Body Fluid Cell Counting—Manual and Urinalysis—Manual Microscopy” for more information.
Q. Do we need to report the cutoff values for medical urine drug testing or does this checklist question apply only to legal testing? We are concerned that clinicians may think the reported cutoff value is the specimen result and not the qualitative result.
A. This question is addressed in chemistry checklist question CHM. 15000, phase II:
Are all patient/client results reported with reference (normal) intervals or interpretations as appropriate?
Note: The laboratory must report reference (normal) intervals or interpretations with patient/client results where such exist. This is important to allow proper interpretation of patient/client data. In addition, the use of high and low flags (generally available with a computerized laboratory information system) is recommended. In urine testing for drugs of abuse, listing the cut-off values for positive results is appropriate.
Medical and legal urine drug testing require that you include the cutoff values for positive results. Positivity or negativity of a test sample is defined by the cutoff used—the same sample can test positive by one cutoff and negative by a higher cutoff. Without cutoff information, it is not possible to obtain meaningful results. Moreover, it is not possible to compare results obtained from different labs or point-of-care locations. The medical director is responsible for making sure the information on the report is clear so physicians can interpret it accurately.
The cutoff values may be listed in the report or on a separate list or table in the chart. If one of the latter is used, it must be rigidly controlled. An additional clarification to the note has been proposed for the next edition of the chemistry and toxicology checklist.
Q. Please elaborate on items three and five in the notes for chemistry checklist question CHM.15250. Our laboratory performs only medical urine drug screen testing, not legal testing. We do not automatically send positive samples for confirmatory testing unless the physician specifically requests confirmation. Does item three in the notes require us to send out all positive samples for confirmation? What should we include in our reports?
A. Chemistry checklist question CHM.15250, phase II, reads:
Are there documented protocols for the reporting of toxicology results?
Note: In addition to the requirements found in the Laboratory General Checklist, the following information must be included in toxicology reports:
- If appropriate, substances or classes of substances analyzed as part of the toxicology test
- Specimen type
- Report status for positive results (i.e., unconfirmed, confirmed, or pending confirmation)
- For immunoassays, the cut-off concentration for a positive result for each drug
- If the report includes unconfirmed screening results, a statement that such results are to be used only for medical (i.e., treatment) purposes. Unconfirmed screening results must not be used for non-medical purposes (e.g., employment testing, legal testing)
The chemistry checklist does not require that all positive urine drug screening results be sent for confirmation. The intent of CHM. 15250 is to ensure that clinicians have appropriate information to interpret results in the patient care setting. The purpose of the checklist note is to ensure that clinicians understand the limitations of the data. Your report should state that unconfirmed positive results are to be used only for medical—that is, treatment—purposes. The report should also include the test status—unconfirmed, pending confirmation, or confirmed. The cutoff values may be listed in the report or on a separate list or table in the chart. If one of the latter is used, it must be rigidly controlled.