4.48: Sample Analysis III, Quantity Not Sufficient (QNS)

A Chemistry technologist is performing sample analysis on a high-throughput analyzer. The printout for one sample indicates that the requested analysis was not performed because of insufficient sample volume. He is about to report the result as QNS when a supervisor intervenes, and asks to see the sample. Once she has seen the sample container, she asks the technologist to view the LIS with her.

QUESTIONS

1. What should a technologist’s response be to a possible QNS?
2. The sample in question in the Chemistry laboratory is in a “bullet” tube and the tests requested for the newborn patient included total bilirubin and electrolytes. In addition, a hepatitis B surface antigen test, ordered on a separate tube but drawn at the same time as the Chemistry tests, is performed in the Serology section. Upon investigation ~5 \(\mu\)L of sample can be recovered from the Serology sample. This is taken and added to the ~10 \(\mu\)L of serum obtained after re-centrifuging the sample. What steps can now be taken to produce results?
3. The results of the analysis on the diluted sample are that total bilirubin, AST and alkaline phosphatase all produced values within the reportable range and were verified in the LIS. Analysis of ALT and albumin did not yield results in the reportable range, and had to be reported as QNS. Can different sample types be used to replace the missing sample? For example, if the required test was for a serum cortisol.

Questions to Consider

1. Why would the supervisor want to see the sample container?
2. What information can be gained on this sample by going to the records in the LIS?
3. What is the value of attempting to find another sample?
4. What additional information is needed before proceeding?
5. What type of tube is normally used for a hepatic profile? Does the methodology permit the use of other sample types?
6. Are certain tests time-dependent?

Answer

1. One of the ongoing problems that technologists are faced with is the problem of having insufficient sample (Quantity Not Sufficient, QNS) to perform a requested analysis. There are several approaches to the problem that a technologist should be aware of.
   1. Try to anticipate a QNS before attempting to perform an analysis. You don’t want to magnify a small problem of a possible insufficient sample to a real QNS. LOOK at the sample before analysis and if you believe that there may be insufficient sample, deal with the problem now (see points 2 & 3 below). EVERY time you are faced with ‘bullets” for babies you must make this decision.
   2. If you believe you might have insufficient sample for the requested analyses before analysis or, if after analysis you are faced with a possible QNS situation, look in the LIS for the previous results on this patient. If previous results are elevated, you can probably perform a dilution that will permit analysis. ‘Bullet’ samples are examples of samples that are often associated with insufficient sample. Very often they are drawn from newborns for bilirubin analysis, which is almost always highly elevated and can take a 10x dilution, or TSH, which are also usually highly elevated.
   3. If more than one test is being ordered and you are trying to deal with a likely insufficient sample, you must make your best decision as to WHICH test you will try to save and report a value. Again, bilirubin for babies is a good choice because the neonatologists always want a bilirubin. If multiple thyroid tests are ordered, try and run the TSH. Electrolytes usually cannot be run on a dilution, but they require very little sample and probably could be salvaged and run.
   4. When in doubt, check with a supervisor. It is critical that you have a good understanding of both the sample volumes AND the ‘dead’ volumes required for each instrument and assay. But please remember a QNS report indicates some degree of failure on the laboratory’s part to deal with a problem and should be used as infrequently as possible.
2. The dead volume of the analyzer is 25 \(\mu\)L; the sample volume for total bilirubin is 10 \(\mu\)L; the sample volume for AST, alkaline phosphatase, and ALT are 5 \(\mu\)L each; and the sample volume for albumin is 3 \(\mu\)L. Since it is believed that the bilirubin assay is most critical for this newborn, the technologist concentrates on this test. Since the total bilirubin was 15 mg/dL the previous day, the supervisor suggests that the technologist take the available sample and prepare a 7-fold dilution, that is 10 \(\mu\)L of sample + 60 \(\mu\)L of 0.15 M NaCl. This will allow measurement of the entire hepatic profile with the possible exception of albumin.
3. Very often a sample drawn at another time could replace a sample drawn at a different time. If the nature of the test is that it does NOT change rapidly with time, then replacement is possible, for example, creatinine. If the analyte tends to change rapidly (e.g., glucose) or is time-dependent (such as cortisol), then replacement is not possible.
   
   In this case, the technologist should speak with the physician to see if the cortisol was specifically a timed sample. If it was, then the alternative sample could NOT be used to replace the missing sample.

Answers to Questions to Consider

1. By looking at the sample container the supervisor can obtain information regarding the possibility of taking steps that would result in the reporting of a quantitative result and not just reporting “QNS”. If the sample container were an aliquot tube (“pour-off”) this would indicate that the primary phlebotomy tube should be available elsewhere in the laboratory and might be processed for additional sample. In addition, if the sample container was a “bullet” tube (a Microtainer tube), this would indicate that the sample was most likely drawn from an infant, whose laboratory results might be highly abnormal for the tests requested.
2. The patient’s records in the LIS may provide information as to how the sample may be saved and a report of “QNS” avoided. By looking at past test results one can determine if any of the current tests requested were previously highly abnormal. For example, recently highly elevated enzyme or bilirubin results would indicate that a small volume of remaining sample could be diluted sufficiently to provide enough sample to perform one or more of the requested tests (see Case History #21 for questions of proper dilution). If after dilution there is still insufficient sample, then the technologist will need to make a judgment as to which tests can be performed (see Case History #22 for questions of prioritizing test analyses). A supervisor and possibly the ordering physician should help in this process.
   
   Another reason for looking into the LIS records is to see if another sample drawn for this patient may be present in the Chemistry laboratory or some other Pathology laboratory. For example, the Serology section usually requires serum samples and additional sample may be available.
3. Very often a patient sample cannot be easily re-drawn. If the patient is being seen as an outpatient (the usual situation), then the patient must schedule an additional clinic visit, which could be costly in terms of time (perhaps a loss of a work day) and money (loss of work, babysitter, etc). So trying to find another sample to replace the missing one can have a very large impact on the patient’s life.
4. The technologist need to know: (a) the dead volume of the analyzer (b) the tests that can be run on the diluted sample (c) the sample volume for each test to be run (d) the reportable range for each test to be run (upper and lower limits)
5. Routine chemistry tests almost always use a serum sample. But, many tests permit the use of heparin and even EDTA anti-coagulated tubes. IF a sample had been sent to the hematology laboratory for a CBC at about the same time as the Chemistry sample, it is possible that that sample could be centrifuged and the plasma used to measure some portion of the hepatic profile tests.
6. Yes, the value of many tests is time dependent. Examples include twenty-four hour urine collections (many analytes), samples drawn after a fast (e.g., glucose), samples drawn after a challenge (e.g., glucose, cortisol, or TRH stimulation test), samples for analytes that have a specific circadian rhythm (e.g., cortisol). For cortisol, the morning (AM) cortisol is usually higher than the afternoon (PM) sample, and the ratio of the AM cortisol/PM cortisol can be used to determine if a patient has possible adrenal gland dysfunction.