Editor’s note: Sandra L. Honigfort, MHA, BSMT(ASCP), answers questions from MLO readers. Sandra is Laboratory Services Coordinator, Infection Prevention Coordinator, at Paul Oliver Memorial Hospital in Frankfort, MI.
Question
We recently had a patient who was receiving Rasburicase, and the physician wanted a Uric Acid done. The drug seems to interfere with the Uric Acid method. I tried to do a company / instrument search to see if there was any info available and I couldn’t find anything. Are you aware of any recent studies?
Answer
Rasburicase (brand name Elitek™) is a drug used for controlling uric acid levels in patients receiving anti-cancer therapies. These therapies can cause increased uric acid levels as a side effect of tumor lysis. The problem in measuring uric acid levels in these patients is that the drug continues to act in the blood samples left at room temperature. There are a number of websites,1 including the Elitek site,2 that describe some sample handling protocols to minimize this effect.
The basic protocol for these specimens requires using a pre-chilled tube containing heparin, which is immediately immersed in an ice bath. Once cooled, the tubes should be centrifuged in a 4°C centrifuge and the plasma then assayed within four hours of sample collection. The chilling slows the action of the drug, lowering the uric acid level.
An Internet search revealed an effective way of alerting personnel and providers of this problem in the University of Iowa’s online testing handbook.3 This pathology department has included a separate test available for patients on Rasburicase which lists the special specimen handling requirements. Another widely used method is to alert providers through special communications (like newsletters) from the pathology department outlining the importance of disclosing the information to the laboratory when ordering the test so that appropriate specimen handling measures are taken to provide accurate results.
References
1. DailyMed. http://dailymed.nlm.nih.gov/dailymed/archives/fdaDrugInfo.cfm?archiveid=9174. Accessed September 19, 2013.
2. ELITEK. http://www.elitek.us/default.aspx. Accessed September 19, 2013.
3. University of Iowa Health Care. Department of Pathology. Laboratory Services Handbook. http://www.healthcare.uiowa.edu/path_handbook/handbook/test2347.html. Accessed September 19, 2013.
Question
I’ve been asked to start reporting a Urine Protein Creatinine Ratio for use with preeclampsia patients. Have there been any recent studies regarding the value of this calculation?
Answer
Significant proteinuria in pregnancy is a hallmark for preeclampsia, a condition that is a major factor in maternal hemorrhage and mortality. The gold standard for detecting proteinuria, the 24-hour urine protein, is a cumbersome test that does not provide timely answers in emergent situations. Therefore, clinicians have searched for alternatives. The urine dipstick protein has not been found to be reliable, mostly due to the varying hydration status of the patient.3 Early studies correlating the urine protein creatinine ratio (UPCR) with 24-hour urine protein results showed mixed results.3 However, some recent studies have been reported that show very good correlation.
An article in the Journal of Family and Reproductive Health1 describes a study using two urine samples collected at 10 a.m. and 4 p.m. for each participant to look at the problem of diurnal variation that may have been a factor in the earlier studies. The authors found that although protein was increased in the afternoon sample, the results of both samples correlated well when compared to the 24-hour results. Another study showed that the UPCR had a positive predictive value of 94% with 95% sensitivity.2 The largest study reviewed tested 116 paired samples vs. 24-hour collections and showed good correlation.3
In all cases the authors concluded that UPCR is a viable alternative to the traditional 24-hour protein measure. It is less cumbersome, can be done on an emergent basis, and in most cases helps to provide a clear diagnosis. The 24-hour collection should be considered only when the results of UPCR are inconclusive (marginal) and other signs of preeclampsia are present.
References
1. Mohseni S, Moez N, Naghizadeh M, Abbasi M, Khodashenas Z. Correlation of random urinary protein to creatinine ratio in 24-hour urine samples of pregnant women with preeclampsia. J Fam Reprod Health. 2013;7(2):95-101.
2. Cade TJ, Gilbert SA, Polyakov A, Hotchin A. The accuracy of spot urinary protein-to-creatinine ratio in confirming proteinuria in pre-eclampsia. Aust N Z J Obstet Gynaecol. 2012;52(2):179-182.
3. Dwyer B, Gorman M, Carroll I, Druzin M. Urinalysis vs urine protein-creatinine ratio to predict significant proteinuria in pregnancy. J Perinatol. 2008;28(7):461-467.
Question
Is it permissible to take a serum sample drawn in a gel SST tube that won’t clot and pour the serum into a green-topped gel lithium tube, mix and spin the sample again, and use this plasma to run tests? We are looking for a miracle to expedite testing on serum samples that take hours to clot and clog up our instrument.
Answer
The literature does not give exact reference to this practice. However, Tietz Fundamentals of Clinical Chemistry states that “blood collected into a tube with an additive should never be transferred into another tube.”1 This would imply that that practice is acceptable if the tube has no additive. In addition, the CLSI-approved guideline for handling and processing blood specimens does give a recommendation for devices to accelerate clotting such as snake venom/thrombin or glass and silica particles that can be added.2 Most gel SST tubes already contain a clot activator. The technical dilemma is whether the clot activator in the tube is actually considered an additive.
It is assumed since the SST tubes do have a clot activator, you are speaking of extreme circumstances when the blood does not clot for “hours.” If this is a frequent occurrence, there needs to be investigation into phlebotomy practices to determine why this is occurring. Clotting is delayed by chilling, drawing above IV sites, and neglecting to invert the tubes to initiate the clot activator. If it really is a rare occurrence, then the patient’s situation needs to be taken into account when making the decision about how to best remedy the situation. If the results are needed emergently, then pouring might be the best choice. If not, then redrawing the patient with a tube containing an anticoagulant that is acceptable for the testing requested or waiting for the sample to completely clot would be the better choice. Routinely pouring over tubes is not a good practice to encourage.
References
1. Ashwood ER, Burtis CA, Bruns DE. Tietz Fundamentals of Clinical Chemistry. 6th ed. St. Louis, MO: Saunders Elsevier; 2008:44.
2. Calam RR, Bessman JD, Ernst DJ, et al. Clinical and Laboratory Standards Institute. Procedures for the Handling and Processing of Blood Specimens; Approved Guideline. Wayne, PA: 2004. CLSI document H18-A3.
MLO’s “Tips from the clinical experts” column provides practical, up-to-date solutions to readers’ technical and clinical issues from experts in various fields. Readers may send questions to [email protected].
