Unnecessary repeated total cholesterol tests in biochemistry laboratory

Introduction We aimed to determine the number of repeated cholesterol (RC) tests and the ratio of unnecessary-repeated cholesterol (URC) tests among patients admitted to Pamukkale University Hospital (Denizli, Turkey) and provide solutions to avoid URC testing. Materials and methods Total cholesterol (T-cholesterol) tests (N = 86,817) between June 2014 and May 2015 were evaluated. The tests performed more than once per patient were determined as RC test (N = 28,811). RC test with an interval shorter than 4 weeks were determined as URC test (N = 3968) according to the shortest retest interval stated in ACC/AHA blood cholesterol guideline. RC testing included internal medicine, surgery and paediatric outpatients and inpatients. Reference change value (RCV) of total cholesterol was calculated. Results The 33.1% of the T-cholesterol tests were RC tests (N = 28,811), 13.7% of them were URC tests (N = 3968). Our RCV value was 25%. The percentage change between consecutive tests was less than RCV in 86.1% (N = 3418) of URC tests. URC tests were performed more frequently in patients with desirable total cholesterol value (P < 0.001). Conclusion There is a significant part of repeated T-cholesterol tests requested in our hospital. URC test requests can be evaluated by laboratories and the obtained data should be shared with clinicians. Laboratories can calculate RCV for the tests they performed and report this value with the test result. To prevent from URC tests, a warning plug-in can be added to hospital information software in accordance with guidelines to prevent from URC test requests.

Cholesterol test is one of the common performed tests in laboratory. Over the last two decades, the number of total cholesterol requests per year increased more than 15-fold (4). Minimum retest intervals are recommended to avoid unnecessary repeated cholesterol (URC) tests (11)(12)(13). According to "National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults III", lipoprotein profile screening should be done once every 5 years in healthy adults above 20 years old (11). The American Diabetes Association (ADA) recommends lipoprotein profile screening at diabetes diagnosis, at an initial medical evaluation and/or at the age of 40 and every 1-2 years (12). American College of Cardiology/American Heart Association (ACC/AHA) blood cholesterol guideline recommends lipoprotein profile monitoring subsequent to initiation of statin therapy and followed by a second lipoprotein panel 4 to 12 weeks after.
Thereafter, monitoring should be performed every 3 to 12 months as clinically indicated (13).
In this study, we aimed to determine the number of repeated cholesterol (RC) test and the ratio of unnecessary repeated cholesterol (URC) tests among patients admitted to Pamukkale University Hospital (Denizli, Turkey) and to provide solutions in order to avoid URC testing.

Study design
The results of all total cholesterol tests which were performed from June 2014 to May 2015 in Pamukkale University Hospital Central Laboratory Biochemistry Department were obtained from the laboratory information management system. Cholesterol tests which were performed during this period (86,817 tests) were evaluated in the study.
Request dates, requesting services and total cholesterol results were determined from the obtained data. The cholesterol tests which requested for once in study period were excluded. The tests which were performed more than once per patient in study period were included and determined as RC test (N = 28,811). Cholesterol retest intervals for RC tests were calculated with the interval between consecutive tests. Any RC test which had an interval shorter than 4 weeks were determined as URC test (N = 3968 tests) according to the shortest interval stated in ACC/AHA blood cholesterol guideline.

Methods
We used the desirable total cholesterol value cutoff as 5.17 mmol/L in our study (11). All tests were run on Roche Cobas c701 chemistry analyser (Roche Diagnostics GmbH, Mannheim, Germany). Two levels of internal quality control (QC) materi-als, total cholesterol control level 1 (mean = 2.43 mmol/L, range: 2.17 -2.68 mmol/L) and level 2 (mean = 4.57 mmol/L, range: 4.11 -5.04 mmol/L) were assayed during the study period. Standard deviation (SD) and coefficient of variation (CV) values for the levels of internal quality control materials were calculated during June 2014 -May 2015 ( Table 2).
Reference change value (RCV), which used for evaluating the clinical significance of changes in consecutive test results from an individual, were calculated for cholesterol tests of our laboratory . RCV was calculated according to naturally occurring variables (analytical CV and within subject CV) (14).

Statistical analysis
Descriptive statistics and chi-square analysis were done using SPSS 17.0 (SPSS Inc., Chicago, IL, USA). Number and percentage of the groups were calculated. RCV was calculated with formulae: Z is the number of standard deviations appropriate to the probability (15). Z value is 2.58 for 99% probability (P < 0.01) (16). CV intraindividual value is 5.95 for total cholesterol (17). CV analytical value was calculated with the mean CV of our level 1 and level 2 internal quality controls. CV was calculated from the internal quality controls data over the one-year period using the following equation: CV (%) = (standard deviation × 100) / laboratory mean (internal quality control).
Our CV analytical value was 3.25%. According to our CV analytical value, we calculated the total cholesterol RCV value, which is specific for our laboratory. Our RCV value was 25%.    (Table 4).

Discussion
Our findings indicate that one of three total cholesterol tests performed in our hospital was RC tests and also 13.7% of these tests were repeated unnecessarily. As we were not able to investigate the clinical features of these patients, we used the shortest retest interval stated at 2013 ACC/AHA blood cholesterol guideline. We consider that, if appropriate retest intervals for different clinical features were used, the rate of URC tests would be higher.
One of the ways to evaluate the significance of difference between measurements is using RCV (18). RCV is caused by changes which are arisen from analytical and biological variation between consecutive tests (19). The percentage change between consecutive total cholesterol tests were less than RCV in 86.3% of the URC tests in our study. This situation suggests that the change below RCV between consecutive URC tests is not associated with clinical intervention in our hospital.

Potential conflict of interest
None declared.