Q & A
Q & A |
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April 2002 Q. Does the CAP have guide-lines for preserving unstained bone marrow slides that remain after a bone marrow examination? Some pathologists have expressed biologic safety issues and concerns about insect attraction. A. No specific guidelines exist for the safe storage of unfixed bone marrow slides or, for that matter, surgical pathology slides that might include unfixed tissue used for frozen sections. Unfixed bone marrow preparations, imprints, and cytological smears should be considered to be contaminated and potentially infectious and should be disposed of accordingly. Because glass slides are sharps they should be placed into a rigid, puncture-resistant, disposable container with a lid and prominent biohazard label. The CAP has established minimum-requirement guidelines for retaining laboratory records and materials. The recommendation for retaining bone marrow smears is 10 years. However, a laboratory may elect to discard unfixed slides after a shorter period because of the biohazards associated with such materials. Thomas A. Merrick, MD Chair, CAP Safety Committee Q. Occasionally, the only vein available for phlebotomy is above an IV. In this case, the phlebotomist will ask the patient's nurse if it's possible to have the IV turned off for a period, and if it is, the phlebotomist often has to wait 30 minutes before drawing from the vein. Is it necessary to wait this long? Is there a recommended time period to wait? For draws other than for coagulation tests, which must be obtained from a line, is there a recommended time to wait after fluids are turned off before the sample is drawn? We have had unreasonable test results when the nurse turns off the fluids, flushes the line with saline, and immediately draws off the 5 cc to 10 cc waste. A. Our suggested approach and recommendations when the only vein available for phlebotomy is above an infusing intravenous line are based on studies by Read et al1 and van Vonderen et al2 as well as recommendations from Daniel Baer, MD.3 Because published information on the subject is sparse, our recommendations also take into account the opinions from pathologists and bioscientific staff within our hospital's Department of Clinical Pathology. Read et al1 investigated 24 volunteers who had five percent dextrose in 0.9 percent NaCl solution infused into one arm. Samples were drawn from the infusion arm (proximal to the IV) while the infusion was running, and then at one, two, and three minutes after the infusion was stopped. The opposite arm was used as the control. The authors concluded that after one minute there was no effect of the infusion on sodium, chloride, or an RBC count. However, after three minutes, the glucose was five percent higher than the control arm. Instead of using healthy volunteers, van Vonderen et al2 studied 10 inpatients and concluded that turning off the IV infusion of 2.5 percent dextrose in 0.45 percent NaCl for three minutes yielded acceptable results for hemoglobin, red cell count, electrolytes, creatinine, glucose, and lactate dehydrogenase. Obviously these two studies are limited, but we considered them a useful basis for developing our own departmental guidelines. We recommend a venipuncture rather than the use of the IV catheter to obtain blood—this is usually possible when a patient has an IV placed in the hand or wrist, since the antecubital fossa is still available for venous access. Our guidelines are as follows: If it is impossible to draw distal to the IV site, the IV infusion should be turned off for three minutes. (This must be timed accurately.) The venipuncture can then be performed above the IV catheter, but the first 5 mL of blood should be discarded. The phlebotomist should include information with the sample indicating what type of fluid was being infused prior to phlebotomy. Exceptions to this protocol are as follows:
As indicated, the phlebotomist or nurse should send information about the infusion contents with the blood sample collected proximal to an IV. This practice enables the medical technologist reporting the results to assess the presence of any infusion-related interference. We also make it clear to our phlebotomists that turning off the IV infusion should be done only by and with the approval of the patient's nurse or physician. In contrast to our protocol, one phlebotomy handbook4 indicates that blood should not be drawn proximal to an IV. If it is not possible to draw below the IV, these authors recommend turning off the IV infusion for at least three minutes and using the IV catheter to collect the blood. Zlotowski et al5 found that 16 of 19 laboratory tests agreed within 99 percent when venipuncture was compared with blood aspirated from peripheral intravenous catheter two minutes following a 200-mL bolus of normal saline. Great care is needed in order not to contaminate or damage the catheter, and this is one of the main reasons we have opted not to routinely use the peripheral IV catheter for blood draws. When drawing blood for noncoagulation tests from an indwelling arterial or central line, the infusing fluid must be turned off prior to sample withdrawal and an initial sample must be discarded. Recommendations vary on the volume to be discarded. One source recommends discarding two times the dead-space volume (catheter volume) for noncoagulation tests and 5 mL or six times the dead-space volume for coagulation tests.4 Other studies have concluded that two to three times6 or even as much as four to eight times7 the catheter volume should be discarded for noncoagulation tests, though the latter study is probably extreme. Studies evaluating discard volumes from arterial or central lines do not generally recommend waiting for a set period before withdrawing the discard fluid or obtaining the laboratory sample. A small number of investigations involving blood draws from an infusing peripheral IV catheter have been performed. A study by Herr et al,8 based on work by Watson et al,9 reviewed use of an 18-gauge IV catheter for phlebotomy and concluded that if the IV was turned off for two minutes, the first 5 mL of sample could be used for electrolytes, BUN, creatinine, and CBC, but a second 5 mL would be needed for an accurate glucose measurement. It is unclear what the catheter volume (dead-space) was in this study.8 In contrast, another source4 recommends stopping the IV infusion for three minutes and discarding two times the catheter volume prior to obtaining blood for lab testing. Published studies that include information about discard volumes do not indicate that the line must be flushed with saline before the sample is withdrawn (as suggested by the reader's question). An important issue that Herr et al,8 Fincher et al,10 and Raisky et al11 raise is the possibility of sample hemolysis if the peripheral IV catheter has a narrow gauge. In conclusion, when obtaining blood from an intravascular cath-e-ter, the most important consideration is the catheter volume and an appropriate discard volume. When drawing from a peripheral venous catheter, turning off the IV for two minutes5,8 or three minutes4 appears to be satisfactory. References Elizabeth Sykes, MD Frederick L. Kiechle, MD, PhD Dr. Kiechle is a member of the CAP Publications Committee. |
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