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COOXIMETRY

Item Value
Approval req'd? no
Available Stat? Yes
Test code COOX, VCOX
Performed by? Hematology
Sendout? no
Price range $$
In House Availability 24 hours/7 days.
Principle The method uses an automatic hemoglobin analyzer. It analyzes whole blood samples for carboxyhemoglobin, methemoglobin, oxygen saturation (fractional), and deoxyhemoglobin photometrically by measuring the absorbance of seven specific wavelengths of light through a thin film of the sample. The instrument's electronics analyze the seven absorbance signals and determine the concentrations of the hemoglobin derivatives. From these concentrations, total hemoglobin is calculated.
Container type air-tight syringe (blood gas kit)
Amount to Collect 1 mL
Collection Instructions Room air contamination is a concern in oxygen saturation determinations. Care should be taken to avoid drawing air into the syringe. If bubbles are present, they should be expelled immediately after drawing the sample by holding the syringe upright and by lightly tapping, so that all air bubbles will rise to the top. Air bubbles can then be expelled out of the opening. The syringe should be securely capped, thoroughly mixed, and placed in ice water.
Sample type heparinized blood (see Additional Information, below)
Normal range
Total Hemoglobin: 14 - 17 g/dL
O2 saturation: 95 - 99%
Carboxyhemoglobin: 0.5 - 1.5% (non-smokers)
Methemoglobin: < 1.5%

Critical values
Carboxyhemoglobin, arterial (COHB) or venous (VCHB): > 14.9 %
Methemoglobin, arterial (METH) or venous (VMEH): > 14.9 %
Synonyms Carboxyhemoglobin;Methemoglobin (METH);Oxygen Saturation;
Stability If a sample cannot be analyzed within 30 minutes after collection, it must be placed in ice water. The sample is stable for two hours in ice water. However, samples from patients with leukocytosis or reticulocytosis will deteriorate more rapidly, and should be analyzed at once.
Interferences Carboxyhemoglobin in newborns appears elevated (usually < 4%) due to the spectral shift associated with fetal hemoglobin. Fetal hemoglobin in the newborn may lead to apparent carboxyhemoglobin levels of 10-12%. High levels of fetal hemoglobin in the newborn, at 90% saturation, have been associated with a 4% overestimate of saturation.

Sulfhemoglobin, sulfa-containing medication, such as dapsone, methylene blue therapy (transient), and freeze-thawing will elevate methemoglobin.
Methemoglobin is reoxidized back to hemoglobin in vitro (analyze within one hour). "Invalid results," i.e., results that are not reliable or interpretable, may be obtained in the presence of elevated levels of methemoglobin, sulfhemoglobin, or interfering substances such as bilirubin. Clinical judgment must be used to test those cases in which cooximetry yields "invalid" results, since reliable confirmatory tests are not available.
Additional information Arterial blood is recommended when oxygen saturation is of prime importance. Venous oxygen saturation values may not be clinically significant without simultaneous study of arterial oxygen saturation. Samples for venous oxygen saturation values reported should be so labeled to allow proper interpretation of the result.
References 1. IL 682 Operator's Manual, Instrumentation Laboratory, Inc. Lexington, MA. (11/03)

2. Whyte RK, Jangaard KA and Dooley, KC. From oxygen content to pulse oximetry; Completing the picture in the newborn. Acta Anaesthesiologica Scandinavica. Supplementum, 1995, 107:95-100.

3. Rausch-Madison S and Mohsenifar Z. Methodologic problems encountered with cooximetry in methemoglobinemia. Am J of Med Sci, 1997 Sep, 314(3): 203-6.

4. Jacobs DS et al. Laboratory Test Handbook, 5th Ed., p. 119. 2001.

5. GEM Premier 4000. Operator's Guide, Revision 01. Instrumentation Laboratory, Lexington, MA. January 2009.
CPT coding 82810
Last Updated 10/7/2013 6:55:37 PM
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