The Effect of Substitution of Plasma for Serum on Chemistry Stat Turnaround Time

Transcription

1 CLNCAL CHEMSTRY The Effect of Substitution of Plasma for Serum on Chemistry Stat Turnaround Time Jerome S. Nosanchuk, MD; Robert Stull, MS; and Robert Keefner, MT(ASCP) Substitution of plasma for serum is analytically sound and can have a salutary benefit on total turnaround time. Since plasma is amenable to high-speed centrifugation, sample separation time can be reduced. Although enhancement of turnaround is clearly possible by use of plasma, other components of preanalytic testing remain the major contributors to total turnaround time. Additional strategies particularly directed at preanalytic factors will have to be employed to reduce total turnaround time substantially. From the Tompkins Community Hospital, thaca, NY. Reprint requests to Tompkins Community Hospital, 101 Dates Dr, thaca, NY (Dr Nosanchuk). Presented in part as an abstract at the ASCPCAP Annual Meeting, October 29 to November 3, 1989, Washington, DC. M ost hospital laboratories are inundated by demands for shortened turnaround times (TATs), especially from emergency rooms and intensive care units. Hilborne and coworkers1 recently attempted to document the extent of the problem, which prompted Valenstein2 to respond editorially questioning the need for faster service. As part of a systematic study of turnaround in our hospital, we looked for strategies that would incur no cost or nomimal additional costs in either operating expenses or capital investment. Substituting plasma for serum in chemistry studies appeared to meet our goal Fig 1. mpact of different centrifuges of spin times. Five minutes in spin time for serum were saved by using Jouan G4.11 instead of an EC Model CU5000 centrifuge. By switching to plasma, spin time was reduced another 4 minutes by the Jouan centrifuge. The StatSpin cut the spin time to 30 sec. Laboratory Medicine Vol. 22, No. 7 July

2 Table 1. Analytes Studied* Plasma Serum nternational Units, Analyte Albumin Alkaline phosphatase Alanine aminotransferase Amylase Aspartate aminotransferase Bilirubin Serum urea nitrogen Calcium Chloride Cholesterol Carbon dioxide Creatine phosphokinase Creatinine Glucose Lactate dehydrogenase Phosphorus Potassium Sodium Total protein Triglycerides Uric acid nternational Units, Conventional Units, 36.8±5.9 gl ± UL UL UL UL 0.102±0.051 mmoll 7.059±6.099 mmoll mmoll mmoll mmoll 29.33±2.66 mmoll UL mmoll mmoll UL 1.208±0.387 mmoll 4.17±0.30 mmoll mmoll gl gl mmoll gl UL UL UL UL mmoll mmoll mmoll mmoll mmoll mmoll UL mmoll mmoll ,29 UL mmoll mmoll mmoll gl gl mmoll gdl UL UL UL UL mgdl mgdl mgdl meql mgdl meql UL mgdl mgdl UL mgdl meql meql gdl mgdl mgdl Conventional Units, ResultllSD gdl UL UL UL UL mgdl mgdl mgdl meql mgdl meql UL mgdl mgdl UL mgdl meql meql gdl mgdl mgdl Correlation Coefficient Since the results are based on paired clinical samples from 20 or more patients, the SD calculations are not unexpectedly wide for some analytes. More importantly, the correlation coefficients are quite good with perhaps the exceptions of chloride and potassium, whose coefficients of variation nevertheless had no adverse clinical impact. of shorter T A T w i t h no significant i n cremental cost. The f o l l o w i n g study demonstrates the time savings achieved using plasma and the analytic performance of plasma compared w i t h serum in our laboratory for 2 1 stat chemistry analytes. We identified additional factors affecting total T A T amenable to manipulation whereby strategies could be devised to minimize global T A T further ^S* E *Z 60 re E o 40 Serum Juuan iviouci A v JOUaM VlUUc p H t p n i n oiaiopin 20 0f j t. 11 Plasm*i V 1\ EC Model CU 5000 Preanalytic Analytic Postanalytic line HUB nine Fig 2. Effect o f s u b s t i t u t i n g plasma for serum a n d alternative centrifuges o n the c u m u l a t i v e m e a n stat t u r n a r o u n d t i m e. T h e differences between preanalytic times i n the g r a p h are due t o the different times required t o process a n d spin samples i n the three diffe rent centrifuges. 466 Laboratory Medicine Vol. 22, No. 7 July 1991 y i aterials and Methods 1 After informed consent was V 1 obtained f r o m selected outpatients and inpatients, paired venous samples f r o m a m i n i m u m of 20 patients were d r a w n into l i t h i u m heparin and SST vacuum tubes (Becton Dickinson, R u t h e r f o r d, NJ). The serum tubes were clotted by the time they were received for chemistry analyses. Three centrifuges w i t h different spin characteristics were available

3 Table 2. Stat Turnaround Time From Time Requisition Received in Chemistry Laboratory to Time Result Reported* Minutes <60 >60<70 >70 nception of Order n Physician's Mind" Writing of Order in Medical Record No. of Specimens (%) 156(82.1) 14(7.4) 20(10.5) 'Excluding blood gases. \ Physician's Response to New nformation Transfer of Order to Requisition Receipt of Result by Physician Transmission of Order to Laboratory Entry of Order in Laboratory Creation of Labels Result Delivery to compare during the study. Samples were centrifuged for 10 minutes at 2,500 rpm in an EC Model CU5000 (nternational Equipment Co, Needham Heights, Mass) or for 5 minutes in a Jouan Model G4.ll centrifuge (Harvey nstruments, Buffalo, NY), allowed to come to a complete stop (about 1 minute), and the serum was separated. Plasma samples were spun immediately in either a Jouan Model G4.ll centrifuge for 1 to 2 minutes at 2,500 rpm or in a StatSpin centrifuge (StatSpin Technologies, Norwood, Mass) for 30 seconds at top speed, and the plasma was separated. The StatSpin stopped almost immediately, whereas the Jouan took between 30 to 60 seconds to stop. The StatSpin could not be used to spin serum. All samples were analyzed within 1 hour of separation from cells or stored frozen until analyzed. Analyses were performed as part of routine chemistry runs on a Hitachi 704 analyzer (Boehringer Mannheim, ndianapolis, nd). Twenty-one chemistry analytes were measured (Table 1) and compared statistically using the Data Statistics Comparisons Program developed by William Dito, MD (Helena Laboratories, Beaumont, Tex). For 10 consecutive days, the time of receipt of all stat requisitions to the time of specimen receipt in the laboratory was recorded. The time interval from specimen receipt to time of presentation to the analyzer was also documented. These combined times made up the preanalytic time. This time study covered all three shifts and specimens from throughout the hospital, including the emergency room. Similarly, data were collected during these 10 days for the Result Verification Transit Time to Obtain Specimen \ Analysis Time Sample Preparation Transit Time to Return With Specimen Fig 3. Cycle of events governing total turnaround time. time required for analyzing the samples on the Hitachi 704 (analytic time) and for reporting of completed results to the physician (postanalytic time). As recommended by Valenstein and Emancipator,3 mean times were calculated. R Table 3. Factors Contributing to Turnaround Time esults Centrifugation time, including stopping, for plasma was 2 to 3 minutes using the Jouan centrifuge and only 30 seconds using the StatSpin (Fig 1). n comparison, it took 11 minutes to separate serum in the EC and 6 minutes in the Jouan centrifuge, including both spin time and time to come to a completed stop. All 21 analytes could be measured in either serum or plasma with our standard instrumentation. The analytical performance for each analyte is listed in Table 1. There were 771 stat specimens collected during the 10-day period. Of these, 190 were for chemistry studies excluding blood gases. Preanaiytical No. of orders No. of tests added on Design of requisitions Transmission of requisition to laboratory Time for phlebotomist to get to patient Time to obtain sample Transport of sample to laboratory Accessioning in laboratory Centrifugation time Delivery of specimen to instrument Analytic nstrumentation Throughput Assay stability Postanalytical Verification process Transmission of result to physician or nurse Figure 2 shows the mean preanalytic time required for collecting a stat chemistry specimen, transporting it to the laboratory, and preparing it for analysis, including centrifugation. The difference between the slowest (serum in EC) and fastest (plasma in StatSpin Laboratory Medicine Vol. 22, No. 7 July

4 Table 4. Strategies for mproving Turnaround Time Preanalytical Fewer orders Simplified requisitions Electronic transmission of orders Adequate No. of trained phlebotomists Adequate No. of conscientious couriers Automated specimen transport Simplified accessioning Faster centrif ugation Analytical Substitute plasma for serum Eliminate centrifugation Whole-blood analysis Transcutaneous analysis Robots Decentralized laboratories High-speed analyzers More stable analyzers Bedside analysis Postanalytical Telephone results Dedicated courier delivery Automated transport, eg, pneumatic tube Electronic transmission Telewriter CRTPrinters ) methods was 10.5 minutes. Mean analysis time is only for the chemistry studies included in Table 1 and, for example, specifically excludes blood gases that are generally collected, analyzed, and reported in our laboratory in less than 20 minutes. Analytic time for the 21 analytes remained constant at about 20 minutes regardless of whether serum or plasma was submitted. Postanalytic (reporting time) was generally 5 minutes or less. Table 2 summarizes the data for total elapsed TAT from receipt of a stat chemistry requisition in the laboratory through acquisition of the specimen, specimen preparation, analysis, and reporting. Eighty-two percent of all stat chemistry studies were completed in 60 minutes or less; 89.5% were completed in 70 minutes or less. However, 10.5% of stat chemistry procedures took more than 70 minutes to completely process. Preanalytic time was clearly the largest component of the total cumulative analytical time (Fig 2). Approximately 70% of the total time was consumed in getting a suitable specimen to the analyzer regardless of whether plasma or serum was used. The maximum difference between using serum or plasma in total TAT was 10.5 minutes, or about 12%. C omment Analysis of plasma instead of serum was clearly faster. Depending on which centrifuge was used, as much as 10.5 minutes could be saved by using plasma. The StatSpin could process only a maximum of two tubes at a time and only a limited sample size (maximum 1.5 ml). Both Jouan and EC centrifuges processed a larger number of specimens and larger sample sizes. Thus, they were more efficient than the StatSpin for processing multiple, simultaneous specimens. The StatSpin, however, may be better for single specimens, small sample volumes, or less busy laboratories. Analytically, there were few meaningful differences between serum and plasma (Table 1). The most notable difference was potassium, which ran 0.17 mmoll lower in plasma than serum. Total protein was 0.29 gdl (2.9 gl) higher in plasma than serum. With the exception of potassium (r=.715) and chloride (r=.831), all analytes had a correlation coefficient of or higher. None of these variances, however, had sufficient clinical impact to prohibit their practical use. Our results parallel the observations comparing serum and plasma analytes made by Lum and Gambino.4 Although substitution of plasma for serum clearly abbreviated stat TAT at little incremental cost to our laboratory, the gain was limited when compared with total TAT. We anticipate that most laboratorians would agree with our experience that the longest element in total TAT is the preanalytic component. n our laboratory, the major contributor to preanalytic time was the time from inception of the order to receipt of the specimen at the analyzer. Similar observations have been made previously by ourselves and others.2'5 n a laboratory with a long mean TAT, eg, consistently over an hour, 468 Laboratory Medicine Vol. 22, No. 7 July 1991 saving 5 to 10 minutes might be only a small achievement. However, if a laboratory were able to process stats consistently in 30 minutes or less, even a 5-minute savings would constitute considerable improvement. Although substituting plasma for serum can improve TAT, it may not be appropriate for all laboratories. Thus, other timesaving strategies need to be devised. n order to develop additional strategies to improve TAT, it is necessary to have a thorough understanding of the complex processes involved in obtaining samples, analyzing them, and reporting completed results (Fig 3). Systems analysis of global TAT allows the total process to be broken down into three major time components: preanalytic, analytic, and postanalytic. Preanalytic time, in our judgment, should be defined as the time from the origin of the idea of a laboratory order in a clinician's mind to the time the specimen is available at the analytical instrument. t is not just the time from receipt of a specimen in the lab to the time it is presented to an analyzer. Analytical time is the actual analysis (machine or bench) time. Postanalytic time is from completion of analysis to receipt of the final result by the clinician. By studying each of these time sectors, we can isolate and identify individual elements contributing to TAT (Table 3). When these factors are known, strategies can be proposed for ameliorating each component (Table 4) and evaluating their relative impact, cost, ease of implementation, and merit. Solutions may involve relatively simple and inexpensive modifications in existing systems, such as redesigning forms to make them easier to read and faster to use or by substituting plasma for serum. Other solutions may require large capital expenditures such as automated specimen transport systems, new instrumentation, or laboratory computerization. The addition of staff phlebotomists, messengers, technicians, clerks, or receptionists will increase operating expenses. Each solution has to be judged by a cost-benefit analysis, both for the laboratory as well as for the entire institution. ssues

5 involving hospital politics become apparent because of competition for limited funds for computers, transport systems, staff, and instrumentation. Since the major contributors to TAT are preanalytic, it should be the area receiving most of our attention. Unfortunately, in most hospitals, the majority of preanalytic factors lie outside the laboratory's direct jurisdiction. For example, the number and quality of messengers or acquisition of automated specimen transport devices are not resources normally under laboratory management's control. The ability of the laboratory to influence those with the ultimate institutional decision-making responsibility will be enhanced by a comprehensive understanding of the problems coupled with well-thought-out solutions whose impact can be defined both qualitatively, ie, improved patient care, as well as quantitatively, ie, a defined shortening of TAT at a given cost per day or per patientq References 1. Hilborne LH, Oye RK, McArdle JE, et al. Use of specimen turnaround time as a component of laboratory quality: A comparison of clinician expectations with laboratory performance. Am J Clin Pathol. 1989;92: Valenstein P. Turnaround time: Can we satisfy clinicians' demands for faster service? Should we try? Am ] Clin Pathol. 1989;92: Valenstein PN, Emancipator KA. Sensitivity, specificity, and reproducibility of fewer measures of laboratory turnaround time. Am ) Clin Pathol. 1989;91: Lum G, Gambino SR. A comparison of serum versus heparinized plasma for routine chemistry tests. Am J Clin Pathol. 1974;61: Nosanchuk JS, Salvatore JD. mproved pneumatic tube system shortens stat turnaround time. Lab Med. 1977;8: Laboratory Medicine Vol. 22, No. 7 July