February 2023 Q&A Readers’ questions answered

Jan. 23, 2023

Do you know if there are criteria for acceptable analytical performance, such as “Target value ± 0.4 mg/dL or ± 20% (greater)”, for plasma free hemoglobin?

Much of the answer to this question depends on a few things and how the quality goals are set, i.e., what is acceptable clinically. In other words, what is the effect of the analytical performance on clinical outcomes and what can be tolerated analytically when knowing what is acceptable clinically. What is the biologic variability? What is state of the art? Often, no simple answer can be given for these questions, and many variables and additional questions can come into play when attempting to answer them. Ultimately, laboratories are responsible for setting their own acceptable analytical performance criteria. Frequently, acceptable proficiency testing (PT) limits (via CAP or other deemed agencies) are used for total allowable error (TEa) if they are available and/or if there is not enough existing information, time, or knowledge to inform other ways of figuring it out.

Here is an AACC article that speaks to the topic a bit: https://www.aacc.org/cln/articles/2021/december/total-allowable-error-tea-how-much-error-can-your-laboratory-allow. The accepted practice for understanding and determining acceptable analytical performance in clinical laboratories is referred to Allowable Total Error (or Total Allowable Error). There are a multitude of publications and sources on this topic as well as lists of defined TEa for various analytes with the accompanying info sources (an example: http://rmbiolab.com/UpFiles/Documents/808edaad-0fb5-4412-9235-2921bf9e8b62.pdf). These sources provide information on how to do the calculations, considerations for different analytes and methods, and how to interpret the results. Regarding free hemoglobin, the information above should provide some ideas on how to approach it but certainly, at a minimum, you would need to understand the capabilities or the particular method used in relation to the needs of the clinical application.

How long is a urine specimen in a cup viable to perform a urine analysis, keeping in mind that a culture is reflexed when necessary? We are inspected by The Joint Commission and need correct information. The lab manager says 4 hours, citing no references; the chemistry supervisor says 24 hours citing no reference. I say it is 2 hours and my reference is the abstract from The National Library of Medicine “Preanalytical requirements of urinalysis” Published online 2014 Feb 15. doi: 10.11613/BM.2014.011.
Do you have a different opinion? If so, can you please cite a reference?

Thank you for this excellent question. Pre-analytical errors account for approximately 70% of all errors in laboratory diagnostics.1 Urine culture is no exception. Urine specimen collection, storage, and preservation significantly affect culture results and thus can negatively impact the diagnosis of urinary tract infections. Improperly collected or preserved specimens can become easily contaminated with bacteria from the periurethral, perineal, and vaginal flora, which can overgrow and mask the presence of true urinary tract pathogens. Perhaps the best resource on this topic is an excellent review published by LaRocco et al, in Clinical Microbiology Reviews in 2016.2

Based on an extensive review of the literature, LaRocco, et al determined that the combination of boric acid and refrigeration (4 to 10°C) is likely able to adequately preserve urine specimens prior to their processing for up to 24 hours. Additionally, the authors found that urine held at room temperature for more than 4 hours significantly increases risk of bacterial overgrowth of both clinically significant and contaminating microorganisms. However, it is worth noting that the overall strength of evidence was not high indicating a need for future systematic studies evaluating the utility of these measures. Urine specimens should include sufficient information indicating both the methodology of collection (i.e., clean catch, catheterization, and so forth) as well as the timing to allow for an informed determination of adequacy and the possibility of contamination.


  1. Lippi G, Chance JJ, Church S, et al. Preanalytical quality improvement: from dream to reality. Clin Chem Lab Med. 2011;49(7). doi:10.1515/cclm.2011.600.
  2. LaRocco MT, Franek J, Leibach EK, et al. Effectiveness of preanalytic practices on contamination and diagnostic accuracy of urine cultures: A Laboratory Medicine Best Practices systematic review and meta-analysis. Clin Microbiol Rev. 2016;29(1):105-147. doi:10.1128/CMR.00030-15.