Description of Event or Problem · 1
WHEN RPTR INTRODUCED COMBINATION BLOOD GAS AND ELECTROLYTE INSTRUMENTS FOR STAT OR TESTING, LAB NOTED THAT INSTRUMENTS USES A CONDUCTANCE METHOD TO DETERMINE HEMATOCRIT AND THAT CONDUCTANCE HEMATOCRITS ARE BIASED 0.3% HIGH WHEN COMPARED TO SPUN HEMATOCRITS. RPTR DEBATED AT THE TIME WHETHER OR NOT TO REPORT THE CONDUCTANCE VALUE, AND DECIDED TO SEND THE RESULT LABELED AS "HEMATOCRIT, CONDUCTANCE" TO DISTINGUISH IT FROM A HEMATOCRIT DERIVED FROM A CBC OR BY CENTRIFUGATION. THIS HAS GENERALLY NOT BEEN A PROBLEM, SINCE THE DIFFERENCES ARE USUALLY NOT VERY LARGE. THERE IS SOME EVIDENCE THAT IN THE FACE OF SEVERE HEMODILUTION CONDUCTANCE-BASED ESTIMATES OF HEMATOCRIT MAY BE MORE UNRELIABLE THAN USUAL. HOWEVER, RPTR HAS A MODERATE AMOUNT OF DATA SUGGESTING THAT THE RECOGNIZED BIAS OF RESULTS VARIES RELATIVELY LITTLE WITH CHANGING HEMATOCRIT, PERHAPS BECAUSE THE INSTRUMENT CONTAINS SOME CIRCUITRY WHICH ATTEMPTS TO CORRECT FOR LOWER HEMATOCRIT VALUES. THE BIAS DOES SEEM TO VARY SIGNIFICANTLY AMONG DIFFERENT PTS, BUT APPEARS TO BE FAIRLY CONSISTENT WITHIN A GIVEN INDIVIDUAL. RPTR RECENTLY HAD COMPLAINT OF A MUCH WIDER DISCREPANCY-NEARLY 10% BETWEEN A CONDUCTANCE HEMATOCRIT AND A SPUN HEMATOCRIT WHICH IS VERY DISCONCERTING, AND SUGGESTS THE NEED TO REVIEW THIS ISSUE, PARTICULARLY BECAUSE LARGE DISCREPANCIES HAVE SEEMED RATHER ERRATIC. PERHAPS THERE IS SOME OTHER UNRECOGNIZED METHODOLOGIC PROBLEM, E.G.,,SETTLING DIFFERENCE OF THE RBCS AND REMIXING OF THE ANTICOAGULANT SAMPLES. BECAUSE CONDUCTIVITY MEASUREMENT IS DEPENDENT UPON ELECTROLYTE CONCENTRATIONS AND THE VOLUME OF SOLUTION BETWEEN TWO ELECTRODES, ANY VARIATION IN THE ELECTROLYTE CONCENTRATION MAY ALSO AFFECT THE HEMATOCRIT VALUE IF NOT TAKEN INTO CONSIDERATION. SOME ANALYZERS THAT SIMULTANEOUSLY MEASURE CONCENTRATIONS OF SODIUM AND POTASSIUM ALONG WITH HEMATOCRIT (CONDUCTIVITY) MAY USE SODIUM AND POTASSIUM VALUES TO CORRECT FOR VARIATIONS THAT MAY BE CAUSED BY THOSE ANALYTES. CHANGES IN OTHER ELECTROLYTE CONCENTRATIONS, HOWEVER, MAY NOT BE TAKEN INTO ACCOUNT. THIS MAY BE OF PARTICULAR IMPORTANCE WHEN MEASUREMENTS ARE MADE ON SPECIMENS TAKEN FROM PTS UNDERGOING HEMODILUTION (I.E., CARDIAC SURGERY). AS CELL VOLUME IS REDUCED BY DILUTION WITH A SPECIAL SOLUTION (CARDIOPLEGIA), THE ELECTROLYTES AND THEIR CONCENTRATIONS MAY VARY DEPENDING UPON THE ELECTROLYTES AND THEIR CONCENTRATIONS IN CARDIOPLEGIA SOLUTION. THE CONSTITUENTS OF THESE SOLUTIONS MAY VARY NOT ONLY FROM INSTITUTION TO INSTITUTION BUT FROM PHYSICIAN TO PHYSICIAN. RPTR DOES NOT BELIEVE THAT THE PROBLEM IS DEVICE OR VENDOR-DEPENDENT , BUT BELIEVES IT IS INHERENT IN THE USE OF CONDUCTANCE TO MEASURE HEMATOCRIT. RPTR HAS NOT BEEN ABLE TO IDENTIFY THE SOURCE OF THE PROBLEM, BUT IT IS REAL. (*).