Which Of The Following Statements Regarding Hemoglobin Analyzers Is False - T-Tees - Your Answers Await, Life's Questions Unraveled

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For blood collection an appropriate Hb screening method should be available so as to accept as many suitable donors as possible and to prevent any inappropriate deferrals. Any new method to be introduced for Hb screening should save time and expenditure and should be validated against major cell counters or direct cyanmethemoglobin method. It is true the capillary method, unlike venous sampling method of Hb estimation in field conditions for HCS/CuSO4/HemoCue is practicable but as our reference method was based on venous samples, to maintain homogeneity and to have near true values only venous samples were used in this study. Also performance characteristics in terms of sensitivity, specificity and PPV, NPV etc. are better with venous samples as compared to capillary samples. Additionally, as donor acceptance policies are based on venous Hb standards and not on capillary Hb values so venous sampling was preferred over capillary for Hb estimation by all these devices. Not many donors in our study were willing to undergo pre-donation sampling twice. We did not want to give two pricks to our donors (one capillary (finger-prick) and other venous sampling) before actual donation hence we used only single venous sampling in our study population.

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Previous studies[8] have used correlation to compare two measurement methods but we decided not to use correlation as it is misleading. Bland-Altman analysis defines, “if two methods are to agree then the mean of the difference between every paired determination will not be statistically different from zero and a limit of agreement can be established”. Our results showed limits of agreement for HCS as 4.7-5.6 g/dl below and above the reference values while HemoCue had values 1.1-1.7 g/dl below and above the reference values which reflected the dispersion of the data around the mean of the difference.

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In our study CuSO4 method inappropriately passed 6.9% of prospective donors, of which a majority (96.7%) were within 1.0 g/dl of threshold against the reference values, which is quite similar to the observations made by James et al.[9] Similarly Boulton et al. observed more inappropriate passes by CuSO4 method with inappropriate passes being within 1.0 g/dl of the threshold for their gender.[10] However, there are studies with contrasting results as well.[11] This difference in results could be due to use of venous samples in our study. CuSO4 has been a traditional way of donor Hb screening despite its limitations. To ensure correct results, CuSO4 solution of accurate specific gravity should be used besides taking other technical precautions. Each drop of blood added to the solution affects the specific gravity, therefore changing the solution daily or at least after 25 tests has been recommended.[12]

The CuSO4 method has also been found to give inappropriate failures and significant number of such failed donors could be recovered with a revised Hb range or by using an alternative screening method.[13] Using a secondary method of screening, many inappropriate donors could be saved that would otherwise be lost. We found copper sulfate inappropriately deferred 1.0% (10/1014) of the prospective donors in comparison to 0.5% (05/1014) of inappropriate deferral using HemoCue. Considering these results, theoretically HemoCue could have saved 50% of the inappropriately deferred donors, though the number of wrong deferrals by both the methods is low. HemoCue is an easy, rapid and reliable method of donor screening,[14] however its use adds extra expense in a donor screening program if implemented as a primary Hb screening method. It is clear from our results that HemoCue is about 500 times costlier than the CuSO4 method and about 40 times costlier than HCS. Although the cost calculations are crude and various other factors viz. cost of lancets, other consumables, electricity charges etc. have not been included, yet implementing HemoCue for primary Hb screening would be beyond reach for many blood centers with limited resources. At the same time, the recovery of inappropriately deferred donors by HemoCue could indicate its usefulness as a secondary screening method.

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Hemoglobin color scale did not show good agreement with reference method. HCS gave 25.2% false results against 7.9% by CuSO4 and 3.1% by HemoCue, with only 23.2% of the readings within ± 1.0 g/dl. It is true Hb discrimination limits in HCS and CuSO4 are different so are not strictly comparable. With the help of Figure 2 (Bland-Altman plots) we have showed limit of agreement for HCS as 4.7-5.6 g/dl below and above the reference values which reflected the data dispersion around the mean of difference. A study by Paddle[15] showed that only 46.08% of readings were correct by HCS and 22.79% results differed more than 2.0 g/dl from the reference value. However, Lewis et al.[16] found HCS more reliable than CuSO4 for Hb testing in blood donors. The HCS method itself is simple and can easily be carried out by even comparatively inexperienced laboratory workers but it is the most subjective of all the methods and further, it is difficult to compare the intermediate values (e.g. 12.5 g/dl) with HCS. This method may be good to assess the prevalence of anemia in general population in peripheral areas but definitely not suitable for Hb screening in prospective blood donors.

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