Blood gas testing and related measurements: National recommendations on behalf of the Croatian Society of Medical Biochemistry and Laboratory Medicine

Background: Manual handling of hemolyzed samples is not standardized and is vulnerable to errors. This study aimed to evaluate laboratory errors due to manual handling of hemolyzed samples and to assess the risk they might have for patient safety. Methods: Data were retrospectively obtained from a laboratory information system for 25 emergency tests from hemolyzed samples. Hemolysis (concentration of free hemoglobin >0.5 g/L) was visually assessed by comparison with a color chart. The reference person reestimated the routinely assessed degree of hemolysis to all samples (n=3185) received in the laboratory in a 1-week period. For each test, the correct and incorrect way of handling results was determined. Risk assessment was performed according to ISO 14971 standard with five categories of risk (S1–S5) and error occurrence (O1–O5). Results: In the studied period, the emergency laboratory received 495 hemolyzed samples (15.5%) with a total of 2518 laboratory test requests (15.5%): 102 (20.6%) of the reports from hemolyzed samples had a comment on hemolysis; 31% of the test results were handled incorrectly (20.7% due to the incorrect release of the test result despite hemolysis interference and 10.3% due to unnecessary suppression), accounting for 4.8% of the total test volume. Tests with the highest combination of risk and occurrence rate were troponin T, potassium and total bilirubin. Conclusions: Manual handling of hemolyzed samples may lead to risk of errors in reporting results for troponin T, potassium and total bilirubin, which may have an effect on clinical decision. In addition, unnecessary suppression of the sample results unaffected by hemolysis could affect patient outcome.

Introduction: Variability among manufacturers of urine dipsticks, respective to their accuracy and measurement range, may lead to diagnostic errors and thus create a serious risk for the patient. Our aims were to determine the level of agreement between 12 most commonly used urine dipsticks in Croatia, examine their accuracy for glucose and total protein and to test their repeatability. Materials and methods: A total of 75 urine samples were used to examine comparability and accuracy of 12 dipstick brands (Combur 10 TestM, ChoiceLine 10, Combur 10 TestUX, ComboStik 10M, ComboStik 11M, CombiScreen 11SYS, CombiScreen 10SL, Combina 13, Combina 11S, Combina 10M, UriGnost 11, Multistix 10SG). Agreement between each dipstick and the reference (Combur 10 TestM) was expressed as kappa coefficient (acceptable κ ≥ 0.80). Accuracy for glucose and total protein was tested by comparison with quantitative measurements on analysers: AU400 (Beckman Coulter, USA), Cobas 6000 c501 (Roche Diagnostics, Germany) and Architect plus c4000 (Abbott, USA). Repeatability was assessed on 20 replicates (acceptable > 90%). Results: Best agreement was achieved for glucose, total protein and nitrite (11/11, k > 0.80) and the lowest for bilirubin (5/5, k < 0.60). Sensitivities for total protein were 41-75% (AU400) and 56-92% (Cobas and Architect); while specificities were 41-75% (AU400, Cobas, Architect). Dipsticks’ sensitivity and specificity for glucose were 68-98%. Most of the dipsticks showed unacceptable repeatability (6/12, < 90%) for one parameter, most prominently for pH (3/12, < 90%). Conclusions: Most commonly used dipsticks in Croatia showed low level of agreement between each other. Moreover, their repeatability varies among manufacturers and their accuracy for glucose and proteins is poor.

Aims Ammonia is an extremely unstable analyte and requires special attention during sampling, transport and storage. The aim of this study was to evaluate the stability of ammonia in lithium-heparin plasma during short-term (at +4°C) and long-term (at −20°C) storage. Methods Twenty plasma samples were used for short-term stability assessment. Each sample was divided into five aliquots and stored in stoppered tubes at +4°C, for 1, 2, 3, 4 and 24 h from initial testing. Fifteen plasma samples were used for long-term stability assessment. Each sample was divided into eight aliquots and stored in stoppered tubes at −20°C for 3, 24, 48 h and 1, 2, 4, 8 and 12 weeks from initial testing. Ammonia concentration was determined on a Beckman Coulter AU2700 chemistry analyser using Randox ammonia enzymatic UV method. Bias was calculated from initial value for each time point and compared with quality specifications defined by Royal College of Pathologists of Australasia. Results The average bias exceeded the total allowable error after storage of samples for 1 h at +4°C and 3 h at −20°C. Conclusion Ammonia is not stable during storage at +4°C and −20°C in lithium-heparinised plasma and should therefore be analysed immediately.