Why centrifuge blood

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Milestone Store. All blood donors must wear a mask regardless of vaccination status. The science behind separating blood and platelets Dan Eberts September 25, Oneblood Blog Subscribe to our blog to read inspiring stories and get the latest news. Follow on Twitter. All Blogs. Centrifugal force is used to separate the components of blood — red blood cells, platelets and plasma — from each other. The result is that the particles with different densities precipitate in layers.

A dose of whole donor blood is placed in a large centrifuge and is spun for a preset time usually about 15 minutes at a preset speed. The red blood cells precipitate to the bottom of the bag, with the platelets above them, then the white blood cells and the plasma at the very top.

The plasma and red blood cells are collected into different bags under optical supervision using a device called the separator. The slopes scatter around the ideal value of 1. For comparison, a normal distribution is depicted. As the values of the constant biases intercepts depend on the measurement range of the analyte, no similar analysis could be performed.

Instead, we analyzed whether deviations accumulate in a certain centrifugation condition. Thus, the aberrant values did not cluster under any centrifugation condition. In six instances, both constant and proportional bias confidence intervals did not include the ideal value. These tests were therefore considered as potentially significantly aberrant. These conditions were listed in table 3. In all but one case, condition 3 was involved as test method, whereby either condition 1 or 2 were reference.

As in all instances, the confidence intervals of the proportional bias and constant bias did not include the ideal values only marginally, we concluded that these outliers were generated only by chance.

In order to enable the readers to make his or her own adjudgment on the significance of these deviations, the scatter plots of all six conditions including the slopes, their confidence intervals, the identity lines and the upper and lower limits of reference where appropriate, are displayed in Figure 3. The scatter plots of the Deming fits mostly aberrant from identity are depicted.

The lower six diagrams group B show tests of which both proportional and constant bias did not indicate identity between the test and the reference method, as listed in table 3. The procedure that has been discussed so far, calculates the probability of identity between the test method and the reference method alpha error.

For the purpose of this study however, the probability of a deviation between the two methods i. The use of patient samples with a sufficiently large measurement range thereby enforced the statistical power.

The first estimate of the beta error according to the description in paragraph 2. All parameters except for chloride were below the allowable limits of the bias, the problem in chloride being the physiologically narrow range of sample values. Second, it was tested whether a specified bias could be detected at the limits of the reference values.

As illustrated in Figure 1 , a bias, named allowable bias on the figure, was pre-specified and the probability calculated that such a bias could be detected.

Five percent of 41 are 2. The bias calculated from the data corresponds to 0. The null hypothesis that the bias is equal or larger than the bias goal can be falsified with high probability, which excludes a deviation with high probability. An illustrative sample of the reference limits tested is given in table 4 and the full information is listed in additional file 2 , table S2.

Interestingly, chloride was within this group. These figures correspond to a cumulative frequency of This indicates that the number of specimens tested were insufficient for cortisol to exclude a bias with sufficient certainty. We conclude that the conditions used including the number of measurements, the analytical range and the analytical imprecision were sufficient to detect a beta error with sufficient probability. Our study shows that the three centrifugation conditions tested deliver identical results.

Moreover, the statistical power was sufficient to exclude any major deviation with a high probability. As mentioned before, very few studies on the influence of different centrifugation conditions on laboratory test results have so far been published [ 1 — 3 ].

In addition, a number of unpublished investigations were made available to us by the manufacturers of tubes or reagents. Our study results do not contradict any of those studies, but rather, they extent both the number of parameters and the test ranges. The number of samples and the spectrum of tests were relatively small in all preceding studies and, as the samples mostly from healthy persons were analyzed, the measurement ranges were relatively narrow, which altogether resulted in a relatively large beta-error.

However, no beta error was ever calculated in the previous studies despite its significance. In this study, a total of data pairs of quantitative clinical chemistry and immunology tests, acquired by comparing six different conditions and three different centrifugation regimens, were analyzed in Deming procedures. Most of the comparisons showed excellent reproducibility indicating that the different centrifugation conditions used did not affect the outcome of laboratory testing.

Corrections of the p-values for multiple testing could be performed, such as the Bonferroni corrections. However, such procedure would increase the beta-error that, in our opinion, is at least as informative as the alpha-error for the purpose of our study.

We preferred to analyze those outlier data to see whether they show any evidence of significant bias, and found evidence of random aberration rather than any statistical significant bias. The only way to ascertain our conclusion on the randomness of outliers would be a repetitious examination under identical conditions to exclude or confirm those aberrant values. We believe that we have provided sufficient data to convince the readers on randomness of these outliers and that the three centrifugation conditions as well as the two different gel separators of Greiner Bio-One provided identical results on a Cobas system of Roche Diagnostics.

The beta errors calculated by two separate methods confirmed a sufficient power of our analyses to detect significant deviations. The first of the two methods relied on regulatory limits either from USA or from Switzerland supplemented with our clinical estimates. The second one tests the biases at the limits of reference values to see whether they exceed a pre-specified bias. The reference limits were chosen for this purpose, as they discriminate between "normal" and "pathological" values, and deviations at these limits would result in "falsely normal" or "falsely pathological" results.

In addition to the quantitative tests, data from 23 qualitative tests or quantitative tests with little or no measurable concentrations did not provide any discrepant results. However, these tests were not statistically evaluated. Our study provided substantial evidences that the centrifugation condition from the WHO guideline, the conditions of 10 min centrifugation time at g and of 7 min at g were equally effective to the performance of the subsequent laboratory analyses.

Each of these conditions can be applied to a broad range of clinical chemistry and immunology tests, provided that specified tubes and analytical conditions were used see section 2.

Laboratories that have been hitherto accommodating the WHO recommendations are now having the possibility of reducing their centrifugation time to less than half of the original amount and in turn, to reduce their overall TAT significantly. Those laboratories that so far are reluctant to switch from serum to heparinized plasma because of the prolonged centrifugation time, can now have a second thought. Clin Lab.

Google Scholar. Clin Chem. CLSI Guidelines, 24 38 :. CLSI Guidelines, 30 10 :. WHO: Use of anticoagulants in diagnostic laboratory investigations. Linnet K: Performance of Deming regression analysis in case of misspecified analytical error ratio in method comparison studies. Anal Chim Acta. Federal Registry. Download references. We thank Ms Tanja Feusi for the skilful technical assistance, the patients and the nursing staff of internal medical wards for their collaboration and Prof.

Schneider-Yin for the linguistic corrections of the manuscript. You can also search for this author in PubMed Google Scholar. Correspondence to Elisabeth I Minder. EIM designed the study and wrote the manuscript, AS organized and supervised the blood drawings on the wards, DM and PN participated in the design of the study, organized and supervised the sample centrifugation and analyses of the samples, KP collected the data and performed the statistical analyses.

All authors read and approved the final manuscript. Additional file The results are displayed as outlined in the legend to table 2. XLS 81 KB. The results are displayed as outlined in the legend to table 4.