A comparison of conductivity-based hematocrit determinations with conventional laboratory methods in autologous blood transfusions

Comparison of four different hematocrit assays and the effect of albumin on their measurements

Clinical decisions are influenced by hematocrit values. Centrifugation (reference standard), conductivity, optical and impedance methods are often used interchangeably to measure hematocrit. The effects of albumin, which are known to affect conductivity methods, have not been evaluated for limits of agreement (LOA) between hematocrit assays in small animals. Canine venous blood was collected from 74 clinical cases and measured by centrifugation (n = 72), conductivity (n = 73), impedance (n = 24) and optical (n = 50) methods. Bland-Altman analysis determined bias (± SD) and 95% LOA between methods. There was a statistically significant difference between centrifugation hematocrit values and values obtained via conductivity (p < 0.0001), optical (p < 0.0001), and impedance (p = 0.0082) methods. The conductivity method underestimated hematocrit by 2.1 ± 2.9% (95% LOA −3.54 to 7.88), the optical method by 3.1 ± 3.6% (95% LOA −4.0 to 10.2), and the impedance method by 2.3 ± 3.7% (95% LOA −5 to 9.6) when compared to centrifuged hematocrit values. The hematocrit difference between conductivity and centrifugation methods was statistically different for low (4%, 0–5%), within reference limits (3%, −5 to 8%), and high (2%, −2 to 5%) albumin values, respectively (p = 0.02), with post-hoc analysis demonstrating that the difference occurred between the low and high albumin groups. This study confirms that albumin values outside reference limits can affect the conductivity method and that hematocrit values obtained via conductivity, optical and impedance methods underestimate values obtained via centrifugation. Therefore, the hematocrit methods cannot be used interchangeably. The wide limits of agreement also demonstrates that care must be taken when making clinical decisions with different hematocrit methodologies.

Back to the "Gold Standard": How Precise is Hematocrit Detection Today?

Introduction

The commonly used method for hematocrit detection, by visual examination of microcapillary tube, known as “micro-HCT”, is subjective but remains one of the key sources for fast hematocrit evaluation. Analytical automation techniques have increased the standardization of RBC index detection; however, indirect hematocrit measurements by blood analyzer, the automated HCT, do not correlate well with “micro-HCT” results in patients with hematological pathologies. We aimed to overcome those disadvantages in “micro-HCT” analysis using “ImageJ” processing software.

Methods

223 blood samples from the “general population” and 19 from sickle cell disease patients were examined in parallel for hematocrit values using the automated HCT, standard “micro-HCT,” and “ImageJ” micro-HCT methods.

Results

For the “general population” samples, the “ImageJ” values were significantly higher than the corresponding values evaluated by standard “micro-HCT” and automated HCT, except for the 0 to 2 month old newborns, in which the automated HCT results were similar to the “ImageJ” evaluated HCT. Similar to the “general population” cohort, we found significantly higher values measured by “ImageJ” compared to either “micro-HCT” or the automated HCT in SCD patients. Correspondent differences for the MCV and MCHC were also found.

Discussion

This study introduces the “micro-HCT” assessment technique using the image-analysis module of “ImageJ” software. This procedure allows overcoming most of the data errors associated with the standard “micro-HCT” evaluation and can replace the use of complicated and expensive automated equipment. The presented results may also be used to develop new standards for calculating hematocrit and associated parameters for routine clinical practice.

Point-of-care versus central testing of hemoglobin during large volume blood transfusion

Background

Point-of-care (POC) hemoglobin testing has the potential to revolutionize massive transfusion strategies. No prior studies have compared POC and central laboratory testing of hemoglobin in patients undergoing massive transfusions.

Methods

We retrospectively compared the results of our point-of-care hemoglobin test (EPOC®) to our core laboratory complete blood count (CBC) hemoglobin test (Sysmex XE-5000™) in patients undergoing massive transfusion protocols (MTP) for hemorrhage. One hundred seventy paired samples from 90 patients for whom MTP was activated were collected at a single, tertiary care hospital between 10/2011 and 10/2017. Patients had both an EPOC® and CBC hemoglobin performed within 30 min of each other during the MTP. We assessed the accuracy of EPOC® hemoglobin testing using two variables: interchangeability and clinically significant differences from the CBC. The Clinical Laboratory Improvement Amendments (CLIA) proficiency testing criteria defined interchangeability for measurements. Clinically significant differences between the tests were defined by an expert panel. We examined whether these relationships changed as a function of the hemoglobin measured by the EPOC® and specific patient characteristics.

Results

Fifty one percent (86 of 170) of paired samples’ hemoglobin results had an absolute difference of ≤7 and 73% (124 of 170) fell within ±1 g/dL of each other. The mean difference between EPOC® and CBC hemoglobin had a bias of − 0.268 g/dL (p = 0.002). When the EPOC® hemoglobin was < 7 g/dL, 30% of the hemoglobin values were within ±7, and 57% were within ±1 g/dL. When the measured EPOC® hemoglobin was ≥7 g/dL, 55% of the EPOC® and CBC hemoglobin values were within ±7, and 76% were within ±1 g/dL. EPOC® and CBC hemoglobin values that were within ±1 g/dL varied by patient population: 77% for cardiac surgery, 58% for general surgery, and 72% for non-surgical patients.

Conclusions

The EPOC® device had minor negative bias, was not interchangeable with the CBC hemoglobin, and was less reliable when the EPOC® value was < 7 g/dL. Clinicians must consider speed versus accuracy, and should check a CBC within 30 min as confirmation when the EPOC® hemoglobin is < 7 g/dL until further prospective trials are performed in this population.

Reliability of Point-of-Care Hematocrit Measurement During Liver Transplantation

BACKGROUND

Although point-of-care (POC) analyzers are commonly used during liver transplantation (LT), the accuracy of hematocrit measurement using a POC analyzer has not been evaluated. In this retrospective observational study, we aimed to evaluate the accuracy of hematocrit measurement using a POC analyzer and identify potential contributors to the measurement error and their influence on mistransfusion during LT.

METHODS

We retrospectively collected 6461 pairs of simultaneous intraoperative hematocrit measurements using POC analyzers and laboratory devices during LTs in 901 patients. The agreement of hematocrit measurements was assessed using Bland-Altman analysis for repeated measurements, while the incidence and magnitude of hematocrit measurement error were compared among 16 different laboratory abnormality categories. A generalized estimating equation analysis was performed to identify potential contributors to falsely low-measured POC hematocrit. Additionally, we defined potential "overtransfusion" in the case when POC hematocrit was <20% and laboratory hematocrit was ≥20% and investigated its association with intraoperative transfusion.

RESULTS

The POC hematocrit measurements were falsely lower than the laboratory hematocrit measurements in 70.3% (4541/6461) of pairs. The median (interquartile range) of hematocrit measurement error was -1.20 (-2.60 to 0.20). Bland-Altman analysis showed that 24.5% (1583/6461) of the errors were outside our a priori defined clinically acceptable limits of ±3%. The incidence of falsely low-measured hematocrit was significantly higher with the presence of concomitant hypoalbuminemia and hypoproteinemia. Hypoalbuminemia combined with hyperglycemia showed significantly larger hematocrit measurement error. Hypoalbuminemia, hypoproteinemia, and hyperglycemia were predictors of falsely low-measured hematocrit. Furthermore, the overtransfusion group showed larger amount of transfusion than the adequately transfused group, with a median difference of 2 units (95% confidence interval [0-4], P = .039), despite similar amount of blood loss.

CONCLUSIONS

Hematocrit measured using the POC device tends to be lower than the laboratory hematocrit measured during LT. Commonly encountered laboratory abnormalities during LT include hypoalbuminemia, hypoproteinemia, and hyperglycemia, which may contribute to falsely low-measured POC hematocrit. Careful consideration of these confounders may help reduce overtransfusion that occurs due to falsely low-measured POC hematocrit.

Measures of Blood Hemoglobin and Hematocrit During Cardiac Surgery: Comparison of Three Point-of-Care Devices

OBJECTIVE

The primary objective was to compare I-Stat, HemoCue, and RapidLab in measurements of the hemoglobin concentration during cardiac surgeries using cardiopulmonary bypass.

DESIGN

Prospective analysis.

SETTING

Single-center, academic, tertiary care cardiovascular center.

PARTICIPANTS

Thirty-four consecutive patients undergoing cardiac surgery requiring cardiopulmonary bypass.

INTERVENTIONS

Blood samples have been collected intraoperatively, and the hemoglobin concentration in each sample was measured, or calculated, simultaneously by the 3 point-of-care devices, HemoCue, RapidLab, and I-Stat.

MEASUREMENTS AND MAIN RESULTS

Correlation coefficients from the regression analysis for HemoCue versus I-Stat, RapidLab versus HemoCue, and RapidLab versus I-Stat were 0.89, 0.96, and 0.88, respectively. Results of the Bland-Altman analysis of the hemoglobin concentration measurements for each device against one another (Fig 1) were as follows: RapidLab versus I-Stat (bias 0.42; 95% confidence interval [CI], -1.05 to 1.89), I-Stat versus HemoCue (bias 0.23; 95% CI, -1.14 to 1.59), and RapidLab versus HemoCue (bias 0.65; 95% CI, -0.17 to 1.47). It appears that I-Stat slightly underestimated the concentration of hemoglobin when compared with both RapidLab and HemoCue. The results of Bland-Altman analysis of each device to a mean Z value (Fig 2) were as follows: RapidLab versus Z (bias 0.36; 95% CI, -0.29 to 1.01), I-Stat versus Z (bias -0.07; CI -0.97 to 0.84), and HemoCue versus Z (bias -0.29; 95% CI, -0.86 to 0.28). Based on the 174 paired samples used for the Pearson moment analysis, the R² values for I-Stat versus HemoCue, I-Stat versus RapidLab, and RapidLab versus HemoCue were 0.79, 0.80, and 0.87, respectively CONCLUSIONS: These data support the interchangeability of these 3 devices for the intermittent intraoperative point-of-care assessment of hemoglobin concentrations in cardiac surgery patients. It is important, however, to consider the possible pitfalls associated with each device when making a clinical decision to transfuse.

Point of care hematocrit and hemoglobin in cardiac surgery: a review

The use of point-of-care blood gas analyzers in cardiac surgery has been on the increase over the past decade. The availability of these analyzers in the operating room and post-operative intensive care units eliminates the time delays to transport samples to the main laboratory and reduces the amount of blood sampled to measure such parameters as electrolytes, blood gases, lactates, glucose and hemoglobin/hematocrit. Point-of-care analyzers also lead to faster and more reliable clinical decisions while the patient is still on the heart lung machine. Point-of-care devices were designed to provide safe, appropriate and consistent care of those patients in need of rapid acid/base balance and electrolyte management in the clinical setting. As a result, clinicians rely on their values to make decisions regarding ventilation, acid/base management, transfusion and glucose management. Therefore, accuracy and reliability are an absolute must for these bedside analyzers in both the cardiac operating room and the post-op intensive care units.

Clinicians have a choice of two types of technology to measure hemoglobin/hematocrit during bypass, which subsequently determines their patient's level of hemodilution, as well as their transfusion threshold. All modern point-of-care blood gas analyzers measure hematocrit using a technology called conductivity, while other similar devices measure hemoglobin using a technology called co-oximetry. The two methods are analyzed and compared in this review.

The literature indicates that using conductivity to measure hematocrit during and after cardiac surgery could produce inaccurate results when hematocrits are less than 30%, and, therefore, result in unnecessary homologous red cell transfusions in some patients. These inaccuracies are influenced by several factors that are common and unique to cardiopulmonary bypass, and will also be reviewed here.

It appears that the only accurate, consistent and reliable method to determine hemodilution and establish transfusion thresholds based on nadir hematocrits during cardiopulmonary bypass, and immediately post cardiac surgery, is with the use of co-oximetry. Perfusion (2007) 22, 179—183.

Analytical evaluation of the epoc® point-of-care blood analysis system in cardiopulmonary bypass patients

OBJECTIVES

The aim of this study was to evaluate the analytical performance of the new epoc® point-of-care blood analysis system in cardiopulmonary bypass patients.

DESIGN AND METHODS

The precision study was conducted on 3 epoc® blood analysis systems using 5 levels of quality control materials twice per day for 5days. The blood specimen was collected in blood gas syringes from 40 cardiac perfusion patients for the comparison study on epoc® (all 3meters), Instrumentation Laboratory GEM4000, Abbott iSTAT, Nova CCX, and Roche Accu-Chek Inform II and Performa glucose meters.

RESULTS

The epoc® blood analysis systems demonstrated clinically acceptable precision for all analytes (from 0.07%, 0.07%, and 0.13% for pH7.6, 7.4, and 7.0 levels; to 3.87%, 3.74%, and 7.56% for pO2 197, 103, and 56mmHg levels). Comparison studies yielded a correlation coefficient R from 0.9201 (sodium) to 0.9969 (pO2) with the GEM4000; from 0.9071 (sodium) to 0.9965 (potassium) with the iSTAT; from 0.8793 (sodium) to 0.9957 (pO2) with the CCX, and 0.9850 and 0.9904 with Roche Inform II and Performa meters respectively. Average biases for all analytes were within the total allowable error limits.

CONCLUSION

The epoc® blood analysis system is acceptable for point-of-care testing in the cardiovascular surgery setting.

Intravenous fluids cause systemic bias in a conductivity-based point-of-care hematocrit meter

BACKGROUND

Point-of-care (POC) devices measuring hematocrit rely on determination of electrical conductivity of whole blood. We hypothesized that some frequently administered IV fluids independently alter blood conductivity and confound hematocrit determination.

METHODS

Whole human blood was diluted to predetermined hematocrit values with normal saline, lactated Ringer solution, hetastarch, or plasma. Electrical conductivity and hematocrit (i-STAT® and spun methods) were measured at each dilution. In separate experiments, the effects of propofol and heparin were noted on these variables.

RESULTS

Greater dilution significantly increased conductivity irrespective of diluent type. The magnitude of the conductivity slopes increased in order for plasma, hetastarch, lactated Ringer solution, and normal saline dilution. Moreover, each slope varied from every other slope (all P < 0.0001), and 94.2% of hematocrit values measured by i-STAT (n = 211 of 224) were less than those for the spun method. Dilution with plasma, normal saline, lactated Ringer solution, and hetastarch caused bias (Bland-Altman limits of agreement) of -2.7% (-6.9/1.4), -4.6% (-7.3/-2.0), -4.8% (-7.8/-1.7), and -2.0% (-5.6/1.9), respectively. The Cohen κ agreement values (5th-95th confidence interval) for a transfusion trigger of 30% were 0.90 (all values, 0.85-0.95), 0.25 (hematocrit <30%, 0.02-0.48), and 0.21 (hematocrit 18%-30%, 0.01-0.42). Clinically relevant concentrations of propofol and heparin had minimal effects on electrical conductivity or hematocrit determination.

CONCLUSIONS

Dilution of blood with frequently used IV solutions affects whole blood conductivity determinations and thereby decreases hematocrits measured by a POC device relying on this method as compared with spun hematocrit. Conductivity-based hematocrit POC devices should be cautiously interpreted when hemodilution is present.

Determination of potassium in red blood cells using unmeasured volumes of whole blood and combined sodium/potassium-selective membrane electrode measurements

Recent studies suggest that the measurement of intracellular potassium concentrations in red blood cells (RBC-K) can be a marker for assessing the risk, development, and treatment of hypertension. In this work, the combined use of miniature potassium- and sodium-selective membrane electrodes is evaluated as a simple means to determine RBC-K. The proposed method requires two separate sets of electrode measurements: (i) potassium and sodium concentrations in the plasma phase of an unmeasured volume of a whole blood sample, and (ii) determination of potassium and sodium concentrations in the same sample of blood after complete hemolysis by ultrasonic disruption of the RBC membranes. The dilution of sodium concentration after hemolysis can be used to determine hematocrit (Hct) (volume of red cells per unit volume of blood) of the blood. The concentration of potassium within the red blood cells (RBCs) is then calculated using the measured change in potassium levels before and after RBCs lysis and the hematocrit level determined from the sodium electrode measurements and/or a conventional centrifugation method. Good correlation for RBC-K between the proposed method and traditional flame photometry is observed for animal blood samples that possess the range of potassium levels found within human RBCs (80-120 mM). However, when potassium is much lower than that found in human RBCs (known to occur for certain animal species), the Hct measured by the sodium electrode method is falsely low, compared to traditional spun hematocrit values, because of an increased level of sodium within the RBCs, necessitating use of spun Hct levels to assess RBC-K accurately. It is envisioned that this new approach could be further miniaturized into a single-use disposable cartridge type electrode system that would enable rapid point-of-care screening of RBC-K levels in human subjects.

Reliability of point-of-care hematocrit, blood gas, electrolyte, lactate and glucose measurement during cardiopulmonary bypass

BACKGROUND

Recently, the GEM Premier blood gas analyser was upgraded to the GEM Premier 3000. In addition to pH, pCO2, pO2, Na+, K+, Ca2+, and hematocrit measurement, glucose and lactate can be measured on the GEM Premier 3000. In this prospective clinical study, the analytical performance of the GEM Premier 3000 was compared with the Ciba Corning 865 analyser for blood gas/electrolytes/metabolites, and for hematocrit with the Sysmex XE 2100 instrument.

METHODS

During a 6-month period, 127 blood samples were analysed on both the GEM Premier 3000 analyser and our laboratory analysers (Ciba Corning 865/Sysmex 2100 instrument), and compared using the agreement analysis for quantitative data.

RESULTS

With the exception of K+, the other parameters (pCO2, pO2, Na+, Ca2+, hematocrit, glucose, and lactate) can be described in terms of the mean and standard deviation of the differences. For K+ measurement, a clear linear trend (r=0.79, p<0.001) in the deviation of the GEM Premier 3000 from the Ciba Corning was noticed, ie, in the lower or upper K+ reference range, the GEM Premier 3000 measured systematically too low or too high, respectively. Furthermore, in comparison with the other parameters, a therapeutically unacceptable systematic difference (mean of difference: -2.2%, p=0.05) in hematocrit measurement on the GEM Premier 3000 was observed for hematocrit values below 30%. The variance of the readings for the GEM Premier 3000 measurements was at clinically acceptable levels.

CONCLUSION

The GEM Premier 3000 analyser seems to be suitable for point-of-care testing of electrolytes, metabolites, and blood gases during cardiopulmonary bypass. However, its downward bias in hematocrit values below 30% suggests that using the GEM Premier 3000 as a transfusion trigger leads to overtreatment with packed red cells.

Point-of-care blood gas analysers: a performance evaluation

Neonates represent a group with unusual sample characteristics and tend to have high hematocrits (Hct). The critically ill patient is also far from ideal with respect to sample type, being prone to either hemodilution or hemoconcentration. Prior to the selection of a point-of-care testing (POCT) analyser for blood gases and electrolytes, we therefore undertook a careful evaluation of some of the performance characteristics of selected instruments. We also conducted an evaluation of one of these systems using patients in the operating room (OR) and the pediatric Intensive Care Unit (ICU). Overall performance for hematocrit determination was acceptable in middle ranges but showed bias at high and low extremes. One system showed significant bias for electrolytes. For the patient evaluation, the system tested, the ABL70 (Radiometer, Copenhagen), showed a small positive bias for Na determinations. It also showed an important bias for pO(2) at levels that are clinically significant. The possibility of operator-related effects on test results has to be eliminated. In terms of ease of use and client satisfaction, the system was well received.

Status of point-of-care testing: promise, realities, and possibilities

Point-of-care testing (POCT) has evolved from the demand for analytical information more rapidly than is available from central laboratories. By bringing the analysis closer to the patient several process steps have been eliminated, facilitating a shorter time to result and faster management response with improved outcomes. Thus benefits include better therapeutic turnaround times, decreased blood loss as a result of reduced phlebotomy secondary to clinical improvement, and diminished resource utilization. These advantages depend on acceptable analytical performance in comparison with central laboratory methods and in relation to clinical criteria. Generally these requirements are met but there are problems particularly with atypical specimens. Outcomes and cost-benefit analyses have been difficult to perform and evaluate. Given the multitude of participants, quality assurance and program management are recognized as resource intensive. However, recognition of problem areas is driving continuous improvement and we envisage expansion of this paradigm.

The use of the iSTAT portable analyzer in patients undergoing cardiopulmonary bypass

OBJECTIVE

To evaluate the utility of the iSTAT blood analyzer, a bedside device for hematocrit, sodium, potassium, and glucose measurement during cardiopulmonary bypass (CPB).

METHODS

Forty patients scheduled for elective CPB were evaluated prospectively. In addition to using the iSTAT analyzer, blood samples were analyzed at four time points: following induction of anesthetic, 10 min. after initiation of CPB, 60 min. after initiation of CPB, and following heparin neutralization by protamine. Blood glucose concentration was measured by the hospital laboratory using a Kodak Analyzer and by a glucose meter, electrolytes were evaluated by the Kodak Analyzer and BGE (a device which is commonly used for "satellite laboratory" determinations of electrolyte and blood gas results), and hematocrit samples were measured by the hospital laboratory using an NE 8,000 and a centrifuge. The means and standard deviations of the differences between the methods were calculated.

RESULTS

The hematocrit values determined by the iSTAT machine, when adjusted for the level of total protein (according to manufacturer's directions), differed from the laboratory values by 0.53 +/- 1.46 percentage points. An alternative to measuring total protein and making the adjustment is simply adding 1% to the hematocrit in the pre-CPB period and 3% on-CPB or post-CPB, which we found to yield values that differed from the laboratory by 0.52 +/- 1.42 percentage points. For all four tests (hematocrit, sodium, potassium, and glucose) the iSTAT had a similar relationship to the laboratory values as did the other commonly used means (centrifuge, BGE, and glucose meter) of clinical evaluation.

CONCLUSION

In summary, we found that in patients undergoing CPB, the iSTAT values agreed sufficiently well with standard laboratory values and that the iSTAT instrument can be relied upon for bedside measurements.

A comparison of four bedside methods of hemoglobin assessment during cardiac surgery

The purpose of this study was to compare the accuracy of conductivity, adjusted conductivity, photometric, and centrifugation methods of measuring or estimating hemoglobin (Hb) with Coulter measured HB as the reference. These bedside methods were studied in 25 cardiac surgery patients during euvolemia and hemodilution and after salvaged autologous red blood cell transfusion. In vivo patient blood samples were obtained before induction, at the start of cardiopulmonary bypass (CPB), after CPB, and after blood transfusion. In 10 patients, blood was sampled in vitro from units of processed blood. Hb values were determined using conductivity by Stat-Crit, adjusted conductivity by Nova Stat Profile 9, bedside photometry by HemoCue, and centrifugation methods. The calculated bias values of Coulter test method Hb (mean +/- SD) for in vivo patient blood samples (n = 90) were: Stat-Crit = 0.6 +/- 0.8 g/dL; Nova Stat Profile 9 = -0.7 +/- 0.4 g/dL; HemoCue = -0.1 +/- 0.2 g/dL; and centrifuge = 0.1 +/- 0.5 g/dL (P < 0.0001). Hb bias values (g/dL) for in vitro samples (n = 10) obtained from processed blood were Stat-Crit = 5.1 +/- 0.6; Nova Stat Profile 9 = 3.0 +2- 0.6; HemoCue = 0.4 +/- 0.4; and centrifuge = 0.6 +/- 0.3 (P < 0.0001). Hb assessment by different test methods may be significantly affected during hemodilution and after blood transfusion. In vitro conditions exaggerated the inaccuracy of conductivity and adjusted conductivity Hb estimates. The rank order of closest approximation to the Coulter measurement for all in vivo blood samples was provided by bedside photometry, followed by centrifugation, adjusted conductivity, and uncorrected conductivity methods.

Bedside hemoglobin measurements: sensitivity to changes in serum protein and electrolytes

OBJECTIVE

Our objective was to compare the effect of protein and electrolyte changes associated with hemodilution on the accuracy of photometric and conductivity hemoglobin determination methods.

METHODS

Blood samples from 10 patients with normal preoperative serum electrolytes and total protein levels were studied. From an indwelling arterial line, 20 ml of blood were removed; hemoglobin values were measured pre-(Baseline) and postdilution by Coulter counter, conductivity, and photometric methods. Blood samples were diluted by placing 4 ml of blood into three test tubes, and adding 1 ml of either 25% albumin, 0.9% sodium chloride, or 5% dextrose in water.

RESULTS

Blood sample dilution resulted in a reported conductivity hemoglobin that was significantly different from the Coulter value (p = 0.0004) when 25% albumin, 0.9% sodium chloride, and 5% dextrose in water solution was used. Using the same dilutions, the photometric method accurately reflected Coulter hemoglobin values. The correlation between photometric and Coulter hemoglobin measurements was R2 = 0.97, p = 0.0001. Correcting the conductivity hemoglobin values for changes in total protein, chloride and sodium significantly improved correlation with Coulter hemoglobin (R2 of uncorrected versus corrected = 0.37 and 0.72; p = 0.0001).

CONCLUSIONS

In the range of electrolyte and protein concentrations found in this study, the photometric method of hemoglobin assessment was more accurate than either corrected or uncorrected conductivity hemoglobin determinations, as compared to Coulter-based measurements.