Letters to the editor
order of draw in the collection process. Several years ago, our institution did a study on calcium levels and order of draw.1 It was determined that the difference in the calcium levels drawn at the beginning of a collection and those collected at the end were significant enough to have an impact on the clinical management of the patient. The individual submitting the question needs to investigate what each site is observing for order of draw. With venous occlusion and time, such analytes as calcium and total protein will be greatly affected. When establishing an order of draw for blood collections, one needs to look at the additives and the tests to be collected (physiological factors). The order of draw that we observe is to have chemistry (especially calcium) collected first when using the evacuated system, or if using a syringe, it must be dispensed from the first syringe (if multiple syringes on a butterfly necessary). Our order of draw when collecting by the evacuated system is: gel separator tubes, red-topped, Citrate, Heparin,
EDTA, Fluoride/Oxalate. If collecting and dispensing from a syringe, our order of draw is: Citrate, Heparin,
EDTA, Fluoride/Oxalate, gel-separator, and red-topped. We realize this differs from the latest NCCLS recommendations, but feel strongly about calcium issues and will continue to use our existing order of draw. Our order of draw more closely resembles the NCCLS guideline of H3-A3 (1991).Even though the gel-separator has an additive acting as a clot accelerator, it should not be put after the Citrate as outlined above. This past June, we conducted a phlebotomy conference at our institution. From talking to individuals from all over the United States and Canada, the order of draw observed seems to be as varied as the institutions represented at the conference. I would refer you to the following resources:J.D. Jones. Journal of Occupational Medicine (May 1980), Vol. 22, No. 5,
p. 316-320.H. Husdan, A.
Rapoport, S. Locke, & D. Oreopoulos. Clinical Chemistry (1974), Vol. 20, No. 5, p. 529-532.J. B. Henry (Ed.) Clinical Diagnosis & Management by Laboratory Methods (1991), Ch. 4: Statland &
Winkel. p. 75.N. W. Tietz (Ed.) Textbook of Clinical Chemistry (1986), p. 480.Ruth Jacobsen, MA, BS, CLS & CLPlb
(NCA)
Mayo Medical Center, Rochester, MN Responding to RAST questionI read with great surprise the answer to the question on RAST posed to Donald Stevenson of Scripps Clinic (Tips from the clinical experts,
MLO, Oct. 2001). He was asked if RAST was still the only laboratory diagnostic test for identifying allergies.First surprise: his answer. He went into the leukocyte histamine assay, which he said has never been of widespread use because of standardization difficulty, feasibility, lack of automation, reliability, etc. Two of the three paragraphs addressed this obscure test. Why?Second, was he speaking of RAST generically or as a specific methodology? It was not clear. If he was speaking
generically, then he was lumping all in vitro assays together, which is no longer appropriate since other assays have supplanted RAST as the de facto standard in vitro specific IgE analysis. I refer you to the June 2000 Journal of Allergy and Clinical Immunology, Brock Williams, et al. Third, he made a point of referring to skin testing as accurate, specific, and reproducible. He further states interference by antihistamines is the limiting variable. This, at the least, is highly misleading to the reader. While it may have sufficient accuracy, it does have a relatively lower (compared to its sensitivity) specificity, and it is not, according to any acceptable laboratory standard, reproducible. Several studies demonstrate its lack of reproducibility across office practices. It does have slightly higher reproducibility by the same practitioner, but variance is still high. In laboratory science, we use controls as one way of proving the efficacy of our testing system. Skin testing purports to measure
IgE, yet no IgE controls are used only histamine control. Are they really measuring histamine when skin testing? An inference must be made about the state of IgE for a given patient. Fourth, while antihistamines preclude testing (without a waiting period), the procedure is invasive and precautionary measures must always be taken. Skin testing is also not quantitative, nor can a Total IgE determination be done.Fifth, IgE-mediated food allergy can be accurately and reliably detected (95 percent confidence) by at least one newer in vitro assay, the ImmunoCAP method, according to Hugh Sampson, MD, Mount Sinai, NY. The reference is Journal of Allergy and Clinical Immunology, May 2001, p. 891-896. Furthermore, the Leukocyte Histamine Release assay has never been of widespread use for food allergy. I might also add that skin testing is not recommended for IgE food allergy testing.Another surprise: One reference? 1964? The short answer to the readers question: No, newer assays have replaced (or at least joined) the 1974 RAST methodology. Physicians now have options for in vitro specific IgE testing. Skin testing is not a laboratory test, but an in-office procedure. In vitro assays are generally for front-line diagnosticians, while in vivo procedures are reserved for specialists. The National Institutes of Health 1997 Asthma Management Guidelines state that in vitro or in vivo procedures are adequate for allergen identification.Steve
Grabosky, MT (ASCP)
Pharmacia Corp.
Scott Depot, WV©
2002 Nelson Publishing, Inc. All rights reserved.
Readers Respond
Addressing order of draw in comparative calcium levelsI read with interest the answer given in the July MLO Tips from the clinical experts column, concerning comparative calcium levels from one hospital clinical lab to the next. One possibility (and the easiest to investigate) has not been addressed in this questionorder of draw in the collection process. Several years ago, our institution did a study on calcium levels and order of draw.1 It was determined that the difference in the calcium levels drawn at the beginning of a collection and those collected at the end were significant enough to have an impact on the clinical management of the patient. The individual submitting the question needs to investigate what each site is observing for order of draw. With venous occlusion and time, such analytes as calcium and total protein will be greatly affected. When establishing an order of draw for blood collections, one needs to look at the additives and the tests to be collected (physiological factors). The order of draw that we observe is to have chemistry (especially calcium) collected first when using the evacuated system, or if using a syringe, it must be dispensed from the first syringe (if multiple syringes on a butterfly necessary). Our order of draw when collecting by the evacuated system is: gel separator tubes, red-topped, Citrate, Heparin,
EDTA, Fluoride/Oxalate. If collecting and dispensing from a syringe, our order of draw is: Citrate, Heparin,
EDTA, Fluoride/Oxalate, gel-separator, and red-topped. We realize this differs from the latest NCCLS recommendations, but feel strongly about calcium issues and will continue to use our existing order of draw. Our order of draw more closely resembles the NCCLS guideline of H3-A3 (1991).Even though the gel-separator has an additive acting as a clot accelerator, it should not be put after the Citrate as outlined above. This past June, we conducted a phlebotomy conference at our institution. From talking to individuals from all over the United States and Canada, the order of draw observed seems to be as varied as the institutions represented at the conference. I would refer you to the following resources:J.D. Jones. Journal of Occupational Medicine (May 1980), Vol. 22, No. 5,
p. 316-320.H. Husdan, A.
Rapoport, S. Locke, & D. Oreopoulos. Clinical Chemistry (1974), Vol. 20, No. 5, p. 529-532.J. B. Henry (Ed.) Clinical Diagnosis & Management by Laboratory Methods (1991), Ch. 4: Statland &
Winkel. p. 75.N. W. Tietz (Ed.) Textbook of Clinical Chemistry (1986), p. 480.Ruth Jacobsen, MA, BS, CLS & CLPlb
(NCA)
Mayo Medical Center, Rochester, MN Responding to RAST questionI read with great surprise the answer to the question on RAST posed to Donald Stevenson of Scripps Clinic (Tips from the clinical experts,
MLO, Oct. 2001). He was asked if RAST was still the only laboratory diagnostic test for identifying allergies.First surprise: his answer. He went into the leukocyte histamine assay, which he said has never been of widespread use because of standardization difficulty, feasibility, lack of automation, reliability, etc. Two of the three paragraphs addressed this obscure test. Why?Second, was he speaking of RAST generically or as a specific methodology? It was not clear. If he was speaking
generically, then he was lumping all in vitro assays together, which is no longer appropriate since other assays have supplanted RAST as the de facto standard in vitro specific IgE analysis. I refer you to the June 2000 Journal of Allergy and Clinical Immunology, Brock Williams, et al. Third, he made a point of referring to skin testing as accurate, specific, and reproducible. He further states interference by antihistamines is the limiting variable. This, at the least, is highly misleading to the reader. While it may have sufficient accuracy, it does have a relatively lower (compared to its sensitivity) specificity, and it is not, according to any acceptable laboratory standard, reproducible. Several studies demonstrate its lack of reproducibility across office practices. It does have slightly higher reproducibility by the same practitioner, but variance is still high. In laboratory science, we use controls as one way of proving the efficacy of our testing system. Skin testing purports to measure
IgE, yet no IgE controls are used only histamine control. Are they really measuring histamine when skin testing? An inference must be made about the state of IgE for a given patient. Fourth, while antihistamines preclude testing (without a waiting period), the procedure is invasive and precautionary measures must always be taken. Skin testing is also not quantitative, nor can a Total IgE determination be done.Fifth, IgE-mediated food allergy can be accurately and reliably detected (95 percent confidence) by at least one newer in vitro assay, the ImmunoCAP method, according to Hugh Sampson, MD, Mount Sinai, NY. The reference is Journal of Allergy and Clinical Immunology, May 2001, p. 891-896. Furthermore, the Leukocyte Histamine Release assay has never been of widespread use for food allergy. I might also add that skin testing is not recommended for IgE food allergy testing.Another surprise: One reference? 1964? The short answer to the readers question: No, newer assays have replaced (or at least joined) the 1974 RAST methodology. Physicians now have options for in vitro specific IgE testing. Skin testing is not a laboratory test, but an in-office procedure. In vitro assays are generally for front-line diagnosticians, while in vivo procedures are reserved for specialists. The National Institutes of Health 1997 Asthma Management Guidelines state that in vitro or in vivo procedures are adequate for allergen identification.Steve
Grabosky, MT (ASCP)
Pharmacia Corp.
Scott Depot, WV©
2002 Nelson Publishing, Inc. All rights reserved.
