Addressing Real and Perceived Clinical Lab Analytical Errors


September-October 2014 - Vol. 3 No. 5 - Page #2

Errors that occur across the spectrum of analytical phases have the potential to significantly impact results, thus compromising clinical outcomes, patient safety, and laboratory efficiency. A case study approach can help to highlight frequently encountered errors associated with blood collection devices and analytical instruments. Looking at such cases and how they present can help to eliminate, or at least mitigate, the effects of preanalytical, analytical, and postanalytical errors on laboratory operations.


Case 1
Hemolysis and Lipemia
A 31-year-old, morbidly obese Native American male was admitted to our facility with hypoxemic respiratory failure and abdominal cellulitis. The lab received multiple grossly hemolyzed and lipemic samples from the floor. The clinician indicated that he wanted the results released, adding that he knew the potassium level would be high. Following denial of that request, we discussed what values he actually needed (electrolytes and creatinine), and suggested he order those, along with an arterial blood gas analysis, which he was planning to draw while the patient was in the ICU.

Case 1 Resolution
Lipid droplets in a highly lipemic sample can cause hemolysis. Experts believe that this occurs either because of direct contact of lipid particles with red blood cells during centrifugation or perhaps because of the detergent effect of saponified free fatty acids. Often, when lipemia-associated hemolysis is identified in plasma samples, omitting the centrifugation step and performing analysis on whole blood ameliorates the problem. In addition, lipemia-associated pseudohyponatremia and pseudohypokalemia can be avoided with this approach.


Case 2
Hemolysis
The patient was a 68-year-old male who had recently undergone a two-week stay at a local hospital with acute kidney injury secondary to IgA nephropathy and Henoch-Schonlein purpura. He had undergone a kidney transplant and was taking steroids and cyclophosphamide, and undergoing dialysis. On this admission, he was diagnosed with septic shock and purulent ascites, with ascites and blood growing Gram-negative rods. Plasma tests requested by the clinician included a basic metabolic panel and magnesium, phosphorus, albumin, and vancomycin levels. Three consecutive samples from a line draw were hemolyzed.

Case 2 Resolution
In making recommendations intended to solve a potential laboratory interference or error, it is always worth considering whether the laboratory test in question should be performed at all. In this case, a review with the care team indicated that each test was, in fact, necessary. However, in many other cases, tests are requested as part of so-called daily labs, and such labs frequently can be skipped if the alternative is a long and potentially costly troubleshooting adventure.

In this case, standard recommendations were made for reducing hemolysis. These recommendations were based on the fact that shear stress often lyses fragile red blood cells; thus, interventions aimed at reducing shear stress during specimen collection are of utmost importance. The recommendations included the use of a larger bore needle (larger diameter reduces shear stress for liquids flowing in a tube), use of a syringe rather than a Vacutainer (syringes can be pulled more slowly with a concomitant reduction in the velocity of blood entering the needle), decanting the specimen into a tube (rather than introducing it into a Vacutainer through a needle), and transporting the specimen to the laboratory by hand, as pneumatic tube systems can subject samples to extremely high accelerations, which may be associated with hemolysis. In some instances, as in the prior case, omitting the centrifugation step and performing the analysis on whole blood is beneficial, but this is possible only when the requested tests can be performed on whole blood specimens.


Case 3
Immunoassay Interferences
The patient was a 54-year-old male with a history of myocardial infarction in 2005; he now has a stent. He was admitted to the surgery clinic for manometry testing secondary to gastroesophageal reflux and chronic belching. While in the clinic, he became lightheaded and had a syncopal episode. The patient was bradycardic, but without chest pain, and an EKG was normal. The patient was brought to the ED for further testing; a troponin level was checked in the main lab, and the value reported was 2.79 ng/mL (reference range <0.4 ng/mL).

Case 3 Resolution
The patient was given oxygen and 325 mg aspirin, and was started on a heparin drip with bolus. Repeat troponin levels were negative; four hours later the level was 0.01 ng/mL. Using a bedside testing platform on two samples collected three hours after the first analysis, the result was 0.00 ng/mL both times. The original sample was centrifuged and rerun with a result of 0.00 ng/mL on the central lab immunoassay system. Cardiology evaluated the patient and thought the elevated troponin level was a false-positive result. The patient was discharged and a Patient Safety Report was filed, accusing the lab of an aliquot error. 

Troubleshooting an immunoassay result that is believed to be falsely elevated can be a challenge. Repeating the test often is helpful, as some types of errors are not repeatable. Investigations into heterophile antibody interference, which usually reveal repeatable false elevations, can include assessing the linearity of signal upon sample dilution or using a heterophile blocking agent. When possible, assaying the sample on another vendor’s immunoassay platform can be beneficial if the interference (ie, heterophile) is specific to the reagents of one vendor’s assay and not another’s.

Here, it appears the initial troponin elevation was a non-repeatable false positive, now thought to have occurred because of microparticulate debris contained in the plasma sample that led to inappropriate ‘sandwich’ formation in the immunoassay. Experts have recognized this problem for some time with select troponin I immunoassays conducted on plasma samples. In fact, it has led several laboratories to institute policies requiring centrifugation and repeating of all positive troponin results. 

Newer data suggest that this problem is lessened when serum samples and thrombin-containing rapid serum tubes are used. In our institution, we use rapid serum tubes for troponin I testing, as well as for a handful of additional immunoassays that have demonstrated non-repeatable false-positive results associated with microparticulate debris in plasma.


Case 4
Additional Potential Immunoassay Interferences
The patient was a 49-year-old female with intellectual disability and a history of gestational trophoblastic disease (GTD). She had a hysterectomy three months prior. Recently, the result of a human chorionic gonadotropin (hCG) hormone assay performed at an outside institution (platform unknown) was reported as 10 mIU/mL. The case was referred to us. The previous institution questioned whether the result indicated a recurrence of disease or represented a false positive result because of a heterophile antibody or some other cause. As in the previous case, troubleshooting began with assaying the sample straight and diluted, in the presence of heterophile antibody blocking reagents, and using a separate vendor’s assay.

Case 4 Resolution
In this case, the results from running the sample straight and diluted were consistent— the heterophile blocking reagent did not reduce the signal and a separate vendor’s assay yielded identical results. After considering these data along with the clinical presentation, we decided that the hCG value was most likely a true value.

In addition to being secreted by trophoblastic tumors and by placentas during pregnancy, hCG can be secreted by the pituitary gland. This is more common among women than men and is of no clinical significance. According to a recent publication,1 it is useful to measure follicle-stimulating hormone (FSH) in such cases, as a high FSH does not occur with a placental origin of hCG. In this case, FSH was 54 mIU/mL, indicating that the source of the hCG was not likely placental. Clinical follow-up demonstrated no recurrence of trophoblastic disease.


Case 5
Potential Specimen Swap
The patient was a 71-year-old woman from an assisted living facility who was admitted with altered mental status. The ED ordered a comprehensive drug screen by gas chromatography-mass spectrometry (GC-MS), which revealed a long list of drugs that the patient should not have been taking. A specimen mislabeling error was suspected because of significant discrepancies between the drug screen and a provided medication list. Interestingly, a nearly identical GC-MS result was obtained for this patient nine months prior on a similar admission.

Case 5 Resolution
In this case, it was initially assumed that the cause of the error was a specimen swap, which is indeed a common reason for wildly discrepant or unexpected laboratory test results. However, the fact that this patient had a nearly identical drug screen result several months prior cast doubt on this theory, as it would be highly unlikely that the patient would have a specimen swapped on two separate dates with other specimens that yielded the same, lengthy list of unexpected drugs.

Additional investigation revealed that the patient had a roommate at her assisted living facility with a similar name, and that the roommate’s drug list matched the drugs found in the patient’s sample. Therefore, the error was in medication administration (the patient and her roommate had been receiving each other’s medications, presumably for many months), and the drug screen result was both analytically valid, as well as clinically explanatory of her altered mental status.

In tracking down the root cause of preanalytical errors, one needs to maintain an open mind about potential causes. As in any diagnostic process, anchoring bias (ie, holding too firmly to a preconceived explanation) can prevent one from entertaining less likely explanations that could, in fact, be true. In this case, the clinical team vehemently insisted that the laboratory had switched samples and was unwilling to consider other potential preanalytical errors. It was not until the clinical chemistry fellow in our department found all of the supporting data, including the roommate’s drug list, that the team settled upon incorrectly administered medication as the explanation.


Case 6
Chemistry Interferences
The patient was a 39-year-old female with bronchiectasis and chronic bronchitis. She had fever and weight loss. Her clinicians requested a creatinine level to assess renal function. Creatinine was found to be elevated, varying between 1 and 2 mg/dL, but other routine chemistry tests were unremarkable.

Case 6 Resolution
While the majority of laboratory errors stem from preanalytical processes, true analytical interferents are still encountered. In this case, a specimen swap was deemed unlikely because the elevated creatinine results were observed using more than one sample. The patient’s drug list was reviewed for common interferents. It was discovered that the patient was taking a cephalosporin. 

The creatinine assay used in the lab employs the Jaffe reaction, in which a color change occurs when creatinine combines with picric acid in an alkaline solution. The color change, which is directly proportional to the concentration of creatinine, is then measured spectrophotometrically. This reaction, however, is somewhat nonspecific; the color change is known to occur when creatinine combines with several other compounds, including ascorbic acid, acetoacetate, and, most relevant to this case, certain cephalosporins.

Potential approaches to cases such as this include cessation of testing (if the testing is not clinically needed), switching the patient’s medication (if the patient can tolerate an alternative drug), and switching the testing methodology (if an alternative test is available). In follow-up discussions with the clinical care team, it was determined that the patient did, in fact, need some form of renal function monitoring, and creatinine was preferred over urea nitrogen. The creatinine assay used on many whole blood analyzers (blood gas instruments) employs an electrochemical detection scheme and a creatinine-specific enzyme, creatinase, which does not have an interference with cephalosporins. Thus, this whole blood creatinine assay was recommended to the clinical care team, and the patient was able to continue the cephalosporin without incident.


Documenting Peculiarities
A final issue raised by case 6 is how the laboratory can best indicate for all current and future care providers that a specific laboratory test is inappropriate for a specific patient. Here, the patient presumably would have yielded accurate creatinine results once the cephalosporin was stopped, but what if the patient needed longer term (chronic) cephalosporin therapy? Or what if the patient had a known heterophile antibody that interfered with one or more immunoassays? 

Currently, no obvious location exists to chart such information within most medical record systems. Documentation of these interferences in a note in the medical record can be helpful, but such documentation can be difficult to find in a large medical record. The addition of laboratory test intolerances in the Allergy List might be more effective, but, as these problems are not technically allergies, they may not belong there. Perhaps simply adding these issues to a Problem List is most appropriate. Because most electronic medical record software is not designed to accommodate critical information about patient incompatibilities with specific laboratory tests, and because electronic medical record software packages vary considerably, users may need to determine the best solution to this problem on a case-by-case basis.  

Reference

  1. Gronowski AM, Fantz CR, Parvin CA, et al. Use of serum FSH to identify perimenopausal women with pituitary hCG. Clin Chem. 2008;54(4):652-656.

Geoffrey Baird, MD, PhD, is an assistant professor of laboratory medicine at the University of Washington in Seattle, as well as an adjunct assistant professor in the department of pathology. He is the director of clinical chemistry at Harborview Medical Center in Seattle, as well as the medical director of laboratories at Northwest Hospital and Airlift Northwest. Geoff’s academic interests include laboratory test utilization management and tissue proteomic assay development.

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