Comparative evaluation of blood collection tubes for clinical chemistry analysis

Optimizing d-mannose and glyceraldehyde concentrations as glucose preservatives without clinically affecting biochemical test results

Objectives: The objectives were to evaluate blood additives that combined lithium heparin (LH)-salt with glyceraldehyde (GLY) or d-mannose (MAN) for preserving glucose levels in plasma samples and to simultaneously determine the compatibility of these additives with 14 other biochemical tests.

Methods

Blood samples from 40 subjects, equally divided into healthy and diabetic groups, were collected using five different additives. The three most effective additives, LH/GLY, LH/MAN, and LH/GLY/MAN, were selected for ensuring the best preservation of glucose levels and compatibility with 14 biochemical tests. One-way analysis of variance was used to analyze the mean paired differences of glucose level and biochemical tests. Simultaneously, the clinical criteria from Johns Hopkins Hospital were used to guide the interpretation and set acceptable thresholds for measurements that exceeded the standards.

Results

The combination of 160 mmol/L GLY, 8.4 mmol/L MAN, and LH, maintained glucose levels at approximately 93.4-93.7 % for healthy subjects and 91.3-92.8% for subjects with diabetes mellitus over 8 h. The mean paired differences of glucose levels in preservation were statistically insignificant. The biases in 14 biochemical tests for LH/GLY/MAN and LH/MAN remained within the acceptable clinical criteria during the 8 h.

Conclusions

Combining 160 mmol/L GLY, 8.4 mmol/L MAN, and LH, proved more effective in maintaining glucose levels than individual additives or the conventional sodium fluoride preservative. It did not yield clinical discrepancies in the 14 biochemical tests during 8 h at room temperature.

Erroneous potassium results: preanalytical causes, detection, and corrective actions

Potassium is one of the most requested laboratory tests. Its level is carefully monitored and maintained in a narrow physiological range. Even slightly altered potassium values may severely impact the patient's health, which is why an accurate and reliable result is of such importance. Even if high-quality analytics are available, there are still numerous ways in which potassium measurements may be biased, all of which occur in the preanalytical phase of the total laboratory testing process. As these results do not reflect the patient's in-vivo status, such results are referred to as pseudo-hyper/hypokalemia or indeed pseudo-normokalemia, depending on the true potassium result. Our goal in this review is to present an in-depth analysis of preanalytical errors that may result in inaccurate potassium results. After reviewing existing evidence on this topic, we classified preanalytical errors impacting potassium results into 4 categories: 1) patient factors like high platelet, leukocytes, or erythrocyte counts; 2) the sample type 3) the blood collection procedure, including inappropriate equipment, patient preparation, sample contamination and others and 4) the tube processing. The latter two include sample transport and storage conditions of whole blood, plasma, or serum as well as sample separation and subsequent preanalytical processes. In particular, we discuss the contribution of hemolysis, as one of the most frequent preanalytical errors, to pseudo-hyperkalemia. We provide a practical flow chart and a tabular overview of all the discussed preanalytical errors including possible underlying mechanisms, indicators for detection, suggestions for corrective actions, and references to the according evidence. We thereby hope that this manuscript will serve as a resource in the prevention and investigation of potentially biased potassium results.

Distribution ratios of ethanol and water between whole blood, plasma, serum, and erythrocytes: Recommendations for interpreting clinical laboratory results in a legal context

This article reviews the scientific literature dealing with the distribution of ethanol and water between whole blood (WB), plasma, serum, and erythrocytes (red-blood cells). Knowledge of the ethanol distribution ratio is important when analytical results derived from hospital clinical laboratories are interpreted in a forensic context, such as during the prosecution of traffic offenders. Statutory blood-alcohol concentration (BAC) limits for driving are defined as the concentration of ethanol in WB and not in plasma, serum or red-blood cells. These bio-fluids differ in their water content and thereby the concentrations of ethanol. Plasma and serum contain ~90%-92% w/w water, WB ~78%-80% w/w and erythrocytes ~64%-66% w/w. The mean plasma/WB and serum/WB distribution ratios of ethanol are therefore expected to be ~1.15:1 (91/79 = 1.15), which is in good agreement with values determined empirically. However, in individual cases, the actual distribution ratio will depend on the person's age, gender, and biochemical and hematological properties of the blood specimen, such as its hematocrit. For legal purposes, we recommend that the concentration of ethanol in plasma or serum determined at hospital laboratories is divided by a factor of 1.2, which would provide a conservative estimate of the co-existing BAC and the chance of overestimating the true value is only 1 in 2000 (0.05%).

Evaluation of Serum and Rapid Serum Separator Collection Tubes for Therapeutic Drug Assays

Appropriate specimen collection and storage is essential to preserve sample integrity and ensure accurate test results. The default collection containers for blood drug concentrations are tubes without gel separators to avoid possible drug adsorption. However, routine chemistry tests are generally collected in gel separator tubes due to their convenient transport and processing; collection of an additional gel-free tube is often required for drug measurements. Citrated whole blood was pooled, spiked with drug, and transferred to three tubes (red, SST gold, RST orange) containing calcium chloride. Blood was allowed to clot, centrifuged and stored at ambient temperature (24 h) or refrigerated (7 days). At defined times, serum drug concentrations were determined (Roche cobas c502). Based on these results, specimen collection requirements were updated to allow serum separator tubes for 17 assays. Of the 21 assays evaluated, 18 displayed acceptable stability in both gel-containing tubes (acetaminophen, amikacin, carbamazepine, digoxin, ethanol, gentamicin, lamotrigine, levetiracetam, lithium, methotrexate, phenobarbital, phenytoin, salicylate, theophylline, tobramycin, valproic acid, vancomycin, voriconazole). Three drugs displayed strong decreases in measured concentrations after storage in one or both gel-containing tubes (total tricyclics, lidocaine, and free phenytoin). Following adoption of gel-containing tubes, 94% of the five most frequently ordered drug monitoring tests in the Emergency Department were collected in serum separator tubes. Evaluation of the stability and accuracy of commonly monitored drugs revealed that the majority were not affected by exposure to gel separator material under conditions similar to outpatient clinic storage, courier transport and laboratory storage. Expanding the collection requirements for appropriate drugs to include gel separator tubes decreases the number of specimens drawn and the complexity of laboratory workflows.

Impact of recentrifugation of blood collection tubes on chemistry and immunochemistry analytes after 24 and 72 hours of refrigerated storage on the Roche Cobas 8000 platform

BACKGROUND

We discovered that blood collection tubes (BCTs) were inadvertently recentrifuged due to improper placement on our automated preanalytical system. This study was undertaken to determine the impact of recentrifugation of blood specimens collected in serum separator (SSTs) and plasma separator (PSTs) tubes after refrigerated storage for 24 and 72 h on the concentrations of chemistry and immunochemistry analytes.

METHODS

Blood was collected from 20 volunteers in SSTs and PSTs, centrifuged, and 36 chemistry and 14 immunochemistry analytes were measured at baseline in single-centrifuged tubes on a Roche Cobas 8000 chemistry platform. After baseline testing, the BCTs were refrigerated for 24 or 72 h, recentrifuged and retested. The results were compared to the single-centrifuged tubes for statistical significance.

RESULTS

Recentrifugation of BCTs after 24 or 72 h of refrigerated storage showed statistically significant increases in lactate dehydrogenase activity and potassium concentration and statistically significant decreases in glucose (except in SSTs after 24 h of refrigerated storage) and CO₂ concentration, but no significant differences in immunochemistry analyte concentrations.

CONCLUSION

It may be safe to report most routine chemistry and immunochemistry analyte concentrations from recentrifuged SSTs and PSTs on the Roche Cobas 8000, which may save time and costs associated with recollection and retesting.