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Background
Anemia is a condition in which the hemoglobin (Hb) concentration in the blood is below a defined level (men: 13.5 to 16.5 g/dL; women: 12 to 15 g/dL; children: 11 to 16 g/dL; and pregnant women: 11 to 12 g/dL), resulting in a reduced oxygen-carrying capacity of red blood cells. About 50 % of all cases of anemia can be attributed to iron deficiency; other common causes include trauma, infections, as well as genetic factors. Chronic anemia can be a consequence of diseases (e.g., HIV infection and renal failure), chemotherapy for hepatitis C, as well as myelosuppressive anti-cancer chemotherapy in solid tumors, multiple myeloma, lymphomas and lymphocytic leukemia. Hemoglobin concentration is the most used parameter to detect anemia, usually determined by portable hemoglobinometers, such us the Cell-Dyn 1200 System multi-parameter hematology analyzer (Abbott Laboratories, Santa Clara, CA), the HemoCue B-Hemoglobin Photometer (HemoCue, Inc., Potomac, MD), and the ITC Hgb Pro Professional Hemoglobin Testing System (International Technidyne Corp., Edison, NJ). Some advantages of these equipments are simplicity and speed in measuring Hb, requiring just a single drop of blood collected in a special cuvette. It is claimed by the manufacturer that the HemoCue is suitable for Hb estimation using capillary, venous and arterial blood samples. Previous evaluations of the HemoCue have revealed conflicting results, with some studies presenting a good precision and accuracy of this equipment, and others emphasizing the need of a better methodological control.
While point-of-care devices for Hb testing are often used in a number of clinical settings, the effectiveness of such testing in the home setting has not been studied.
Chen et al (1992) evaluated the HemoCue device for rapid estimation of Hb concentration in a clinical setting. Repeatable accuracy of capillary, venous and arterial samples was examined and then compared with standard laboratory venous Hb estimates using a "Coulter JT" analyzer in 42 patients. The mean values for Hb (g/L) and coefficient of variation (CV) were capillary 108.2 (8.0); venous 104.9 (2.2); arterial 105.9 (2.0); and laboratory venous 104.6 (1.3). Although the mean Hb values were similar, capillary samples were significantly less repeatable than venous or arterial samples (Pitman test, p < 0.001). Comparison of variance between the laboratory sample and each sampling technique demonstrated that capillary samples were significantly more variable than venous or arterial samples. Peripheral skin temperature did not influence the accuracy of capillary samples. HemoCue estimations of venous samples were found to be as accurate as laboratory estimations. The authors concluded that the lack of repeatable accuracy of capillary estimations was sufficiently large that their use can not be recommended in clinical practice.
Conway and colleagues (1998) examined concerns regarding clinically important discrepancies between repeat HemoCue Hb measurements from single drops of blood. Two biomedical scientists and 2 health visitors each obtained a series of paired Hb values by fingerprick sampling from healthy volunteers. Seven of 20 paired values obtained by health visitors and 3 of 20 obtained by scientists from the 1st drop of blood forming at the puncture site differed by greater than or equal to 10 g/L; 11 of 20 paired values obtained by health visitors and 1 of 20 by the scientists from the 4th drop of blood differed by greater than or equal to 10 g/L. After collecting and mixing a number of drops in ethylene-diamine-tetraacetic acid (EDTA) tubes before analysis, 7 of 40 paired values differed by greater than 5 g/L, and none by greater than 10 g/L. Pooling drops of blood before analysis improves precision of HemoCue Hb measurement and allows users to achieve results comparable to those obtained by experienced laboratory staff. The authors concluded that measurement of Hb from single drops of skin puncture blood should be discontinued.
Neufeld and co-workers (2002) evaluated the comparability of Hb concentration in venous and capillary blood measured by HemoCue and an automated spectrophotometer (Cell-Dyn) and documented the influence of type of blood (capillary or venous) and analysis method on anemia prevalence estimates. Between February and May 2000, capillary and venous samples were collected from 72 adults and children and assessed for Hb using the HemoCue and Celldyn methods. Estimated Hb levels were compared using the concordance correlation coefficient and Student's t test for paired data. The sensitivity and specificity for anemia diagnosis were estimated and compared between type of blood and method of assessment. Capillary blood had higher Hb (+0.5 g/dL) than venous blood in adults and children, as did samples assessed by Celldyn compared to HemoCue (+0.3 g/dL). Specificity to detect anemia was adequate (greater than 0.90) but sensitivity was low for capillary blood assessed by HemoCue (less than 0.80). The authors concluded that the difference in Hb between venous and capillary blood is likely related to biological variability. Hemoglobin concentration in capillary blood assessed by HemoCue provides an adequate estimation of population anemia prevalence but may result in excess false negative diagnoses among individuals. The results of this study emphasized the importance of sample collection technique, especially for children. Method of analysis and sampling site need to be taken into consideration in field studies.
Bhaskaram et al (2003) compared HemoCue and cyanmethemoglobin methods for Hb estimation. In 100 apparently healthy children aged 1 to 6 years, Hb was estimated using HemoCue and cyanmethemoglobin methods from finger prick blood sample. The results obtained by the 2 methods were compared using appropriate statistical methods. Mean +/- SD values for Hb (g/dL) were 9.33 +/- 2.719 by HemoCue and 8.14 +/- 2.448 by cyanmethemoglobin method. When assessed by HemoCue method the proportion of children with anemia was 66 % while it was 88 % with cyanmethemoglobin method. The sensitivity of HemoCue method was 0.75 and specificity 1.0 considering cyanmethemoglobin method as gold standard. The corresponding values by cyanmethemoglobin method for a given HemoCue value fell within the mean difference +/- 2 SD with correlation coefficient being r = 0.922. Despite the good association, the 2 methods agreed, the magnitude of difference being -1.19 g/dL (confidence interval [CI]: -1.40 to -0.98) thus suggesting an over-estimate of HemoCue values ranging from 10 to 15 %. A correction factor was arrived for converting Hb values obtained by HemoCue method to arrive at the expected value by the reference method, this factor being 0.389 + 0.831 Hb (HemoCue). The authors concluded that as there are limitations expressed for both the methods in accurately estimating Hb, it is difficult to decide whether one is an over-estimate or the other an under-estimate. By virtue of the principle involved in estimating Hb, cyanmethemoglobin method may be taken as an indirect indicator of iron status. However, it is unclear if such a principle is involved in estimating Hb by HemoCue. Thus, these 2 methods need to be further validated against a sensitive and specific indicator for iron status like circulating transferrin receptor to decide which of the methods can be used to accurately determine the prevalence of iron deficiency anemia in the community.
Paiva et al (2004) determined the precision and agreement of the Hb measurements in capillary and venous blood samples by the HemoCue and an automated counter. Hemoglobin was determined by both equipments in blood samples of 29 pregnant women. The HemoCue showed low repeatability of Hb measurements in duplicate in capillary (coefficient of repeatability [CR] = 0.53 g/dL, CV = 13.6 %) and venous blood (CR = 0.53 g/dL, CV = 13.6 %). Hemoglobin measurements in capillary blood were higher than those in venous blood (12.4 and 11.7 g/dL, respectively; p < 0.05). There was high agreement between Hb in capillary blood by the HemoCue and in venous blood by the counter (intra-class correlation coefficient = 0.86; p < 0.01), and also between the diagnosis of anemia by both equipments (kappa = 0.81; p < 0.01). The authors concluded that while the HemoCue is useful in both clinical and epidemiological settings, especially in situations of emergency, it is more appropriate to use capillary blood samples, considering the sampling error. Furthermore, it is necessary to have a thorough training to minimize poor repeatability of this equipment.
In a prospective study, Eekhof and Groeneveld (2008) examined if the HemoCue Hb value measured in fingertip skin puncture blood corresponds to the reference value measured in venous blood. In 2 health centers, patients' blood was first drawn from a fingertip skin puncture and Hb was measured with the HemoCue method. The same patients were sent to the regional laboratory for laboratory Hb determination. Agreement between the 2 Hb values was assessed using the method of Bland and Altman. Both Hb measurements were carried out in 58 patients. The mean HemoCue Hb was 8.0 mmol/L (95 % CI: 7.6 to 8.4) and the mean venous Hb was 8.2 mmol/L (95 % CI: 7.9 to 8.6). Of all values, 2 were above the level of agreement of 2 SD and 17 values were above the level of 1 SD. The sensitivity of the HemoCue measurement was 81 % (95 % CI: 62 to 100) and the specificity 95 % (95 % CI: 88 to 100). In the population investigated, with a prevalence of anemia of 28 %, the predictive value of a positive HemoCue result was 87 % and of a negative result 93 %. The authors concluded that according to the test characteristics, the HemoCue is a good device for Hb determination. However, in several cases there is a significant difference between the Hb measured with the HemoCue method and the laboratory Hb value. If a reliable Hb value is needed, a laboratory venous Hb assessment is preferred.
In summary, there is a lack of evidence demonstrating that self-monitoring of Hb would result in improved health outcomes in persons with chronic anemia.
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