Study Case: Effects of Oxyglobin^® on Complete Blood Count and Blood Chemistry

Class of 2005 (Legato) and Department of Pathology (Tarpley, Moore, Latimer,), College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7388

Signalment: Canine, Golden retriever, 9-year-old, male

Presenting problems: Presented for severe anemia and thrombocytopenia diagnosed by the referring veterinarian. Previously treated by the referring veterinarian with doxycycline, prednisone, and Oxyglobin^®.

Physical examination findings: Depression and lethargy, pale skin and mucous membranes, slow capillary refill time (3 seconds), tachycardia (HR=180 bpm), tachypnea (RR=45 bpm), hypothermia (T=95.6°F), and epistaxis.

Laboratory Data:

Problems -

1. Severe anemia

a. Severe, normochromic, nonregenerative anemia (Days 1 and 3) with marked thrombocytopenia.

b. Severe, macrocytic, hyperchromic, nonregenerative anemia with moderate thrombocytopenia (Day 6).

The corrected reticulocyte percentages are 0.20, 0.04, and 0.19 for days 1,3, and 6, respectively. Based on these percentages, the anemia is considered nonregenerative though very slight improvement occurred between days 3 and 6. The cause of anemia is unknown. The combination of anemia with thrombocytopenia could be observed with marked blood loss (e.g., hemorrhage), immune-mediated destruction of both erythrocytes and platelets (Evan’s syndrome), or ineffective production of both cell types. Epistaxis was noted in this case and could be attributable to severe thrombocytopenia (due to the causes listed above as well as disseminated intravascular coagulation) or other coagulopathy. Cases of acute blood loss and immune-mediated destruction of erythrocytes are often associated with an elevated MCV and a decreased MCHC due to the presence of a marked regenerative response (and the release of polychromatophilic cells or reticulocytes). Chronic blood loss may lack signs of regeneration and MCV and MCHC are either within or below reference intervals. Oxyglobin^® administration typically results in decreased hematocrit values due to dilution of erythrocytes. Total hemoglobin concentration, the summation of hemoglobin within erythrocytes and plasma hemoglobin, is usually increased since Oxyglobin^® is extracellular hemoglobin that is infused into the vascular system. In this case, an approximate 2.5-fold increase in hemoglobin concentration was observed on Day 3, though this most likely is falsely elevated due to dehydration (see "azotemia" below). The slight increase in MCV may be attributable to the slight increase in reticulocytes observed on Day 6 (in comparison to Day 3). Increases in both MCH and MCHC are most likely due to the assumption that all measured hemoglobin is intracellular, which is not the case with Oxyglobin^® administration. The increase in platelet concentration may be attributable to corticosteroid therapy, which decreases platelet destruction and antibody production, may stimulate platelet production, and may increase capillary resistance to hemorrhage.

2. Mild leukocytosis (day 6). General causes of leukocytosis include physiologic mechanisms (e.g., fear, excitement, or struggling during venipuncture), stress with endogenous cortisol release, or an increased tissue demand for neutrophils. The precise cause of the leukocytosis is undetermined.

3. Azotemia with hyperproteinemia. Azotemia is observed on Days 1, 3, and 6, with the highest value being on Day 3. Measurement of BUN is not affected by the presence of Oxyglobin^® regardless of instrumentation; creatinine values may be incorrect for the majority of analyzers used. Considerations for azotemia include prerenal, renal, and postrenal causes; a urine specific gravity would be helpful in accurately determining the basic etiology of the azotemia, but it is unknown in this case. A creatinine value within the reference interval and an elevated total protein on Day 1 increases suspicion of prerenal causes such as hypovolemia /dehydration. Hyperproteinemia would be better evaluated if the albumin concentration were known. Serum protein measurements are often increased with Oxyglobin;^® peak protein concentrations of 9.9 to 14.6g/dL may be observed at the recommended dose. The measurement on Day 1 is prior to Oxyglobin^® therapy.

4. Increased alanine aminotransferase. With recommended dosages of Oxyglobin,^® ALT measurement remains accurate when Hitachi analyzers are used. However, other analyzers may give invalid results. Hitachi instrumentation was used on Days 3 and 6 (instrumentation is unknown for Day 1). An increase in ALT is observed on Day 6 which most likely is attributable to hepatocellular injury that can occur secondary to tissue hypoxia resulting from severe anemia and possible dehydration.

5. Mild hyperglycemia. Glucose concentration can be accurately measured with Hitachi analyzers after Oxyglobin^® administration. The elevations observed are mild and could be attributable to postprandial measurement or mild stress.

6. Mild hypocalcemia. Measurement of calcium concentration is unaffected by Oxyglobin^® administration for nearly all analyzers. Exclusion of pseudohypocalcemia cannot be done without an albumin measurement. Values for albumin may be invalid regardless of the analyzer used after Oxyglobin^® treatment.

Case Summary - This dog had severe anemia that was treated with the administration of Oxyglobin.^® This patient only showed minor improvement clinically or in erythrocytic parameters five days post-treatment with Oxyglobin.^® The patient subsequently was euthanized. Necropsy and histopathology failed to demonstrate evidence of an adequate erythropoietic response in the bone marrow. These were consistent with a terminal hemolytic anemia.

Oxyglobin^®, a product of the Biopure Corporation, is a hemoglobin-based oxygen carrier (HBOC) that has been used to successfully treat anemia of various causes in dogs. Oxyglobin^® helps to stabilize anemic dogs, providing oxygen-carrying support and thus reduces clinical signs until the patient’s bone marrow is able to regenerate erythrocytes. When given at the recommended dose, Oxyglobin^® has a half-life of 18-26 hours and is expected to be cleared from the plasma within 4-5 days.

Different analyzers and lists of tests whose results are unaffected by the presence of Oxyglobin^® are shown in the Table A below. Experimental data of human blood samples concerning the effects of a hemoglobin-based oxygen-carrier (HBOC-201; now Oxyglobin^®) on CBC variables and WBC differential variables measured with the Cell-Dyn 3500 indicated no interference in the following measured or calculated variables: HCT, RBC count, platelet count, WBC count, MCV, MPV, RDW, and individual leukocyte concentrations. Hemoglobin concentration is accurate as long as it is measured and not based on a calculation using the red blood cell count.

Presence of Oxyglobin^® essentially causes no interference with sodium, potassium, and chloride determinations, which are usually measured by ion-specific electrodes (including Hitachi analyzers). Creatinine may be affected depending on the analytical method used; enzymatic test methods are unaffected whereas colorimetric tests are inaccurate. Analytes that are measured on the Hitachi 912 by colorimetric methods include total protein, albumin, ALT, AST, GGT, LDH, ALP, amylase, magnesium, phosphorus, direct and total bilirubin. Following Oxyglobin^® administration, total protein, albumin, amylase, magnesium, phosphorus, direct and total bilirubin may be inaccurate. However, ALT, AST, GGT, LDH, ALP activities are measured at a wavelength of 340 nm and may be reasonably accurate. In summary, Oxyglobin^® does not interfere with most analytes of the highest urgency in the critical care setting.

Table A. Accurate analytes by instrumentation at plasma hemoglobin = 4.0 g/dL*, Biopure Corporation, 11 Hurley Street, Cambridge, MA 02141, <www.biopure.com>.

Though a urinalysis is not reported here, tests on the urine dipstick, such as pH, glucose, ketones, and protein, are inaccurate as long as the urine is grossly discolored because these tests are colorimetric. The urine sediment examination and urine specific gravity are not affected by the presence of Oxyglobin^®.

References

1. Belgrave RL, Hines MT, Keegan RD, Wardrop KJ, Bayly WM, Sellon DC: Effects of a polymerized ultrapurified bovine hemoglobin blood substitute administered to ponies with normovolemic anemia. J Vet Intern Med 16:396-403, 2000.

2. Callan MB, Rentko VT: Clinical application of a hemoglobin-based oxygen-carrying solution. Vet Clin North Am Small Anim Pract 33: 1277-1293, 2003.

3. Clinical Reference Guide: Oxyglobin Solution, Brochure, published by Biopure Corp, 11 Hurley St, Cambridge, MA 02141, www.biopure.com .

4. Kirby R, Duffy TC: Resuscitation in gastric dilatation-volvulus syndrome. Compend Cont Educ Pract Vet, Suppl 23:8-11, 2001.

5. Latimer KS, Mahaffey EA, Prasse KW (eds): Duncan & Prasse’s Veterinary Laboratory Medicine: Clinical Pathology, 4th ed. Ames, Iowa State Press, 2003.

6. Mott J, Crystal MA: Treating flea anemia with Oxyglobin^®. Compend Cont Educ Pract Vet, Suppl 21(H): 11-16, 1999.

7. Plumb DC: Veterinary Drug Handbook, 4^th ed., Iowa State Press, 2003, p. 960.

8. Various authors, 2002, IMHA: New Perspectives on a challenging disease, Pamphlet sponsored by Biopure Corp, Published by Thomson Veterinary Healthcare Communication, Lexena, KS, pp. 1-16.

9. Ma A, Monk TG, Goodnough LT, McClellan A, Gawryl M, Clark T, Moreira P, Keipert PE, Scoot MG: Effect of hemoglobin- and perflubron-based oxygen carriers on common clinical laboratory tests. Clin Chem 43:1732-1737, 1997.

10. Callas DD, Clark TL, Moreira PL, Lansden C, Gawryl MS, Kahn S, Bermes EW Jr: In vitro effects of a novel hemoglobin-based oxygen carrier on routine chemistry, therapeutic drug, coagulation, hematology, and blood bank assays. Clin Chem 43:1744-48, 1997.

11. Rentko VT, Sharpe TA: Red blood cell substitutes. In: Feldman BF, Zinkl JG, Jain NC (eds): Schalm’s Veterinary Hematology, 5th ed. Philadelphia, Lippincott Williams and Wilkins, 2000, pp. 874-877.

Acknowledgement

"Companion", the image of the Golden Retriever is from the Art Gallery at the website of Dino the Golden Retriever.

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