Blood Draw Site and Analytic Device Influence Hemoglobin Measurements

Abstract

Anemia is a continuing global public health concern and a priority for international action. The prevalence of anemia is estimated from the hemoglobin (Hb) levels within target populations, yet the procedures for measuring Hb are not standardized and different approaches may result in discrepancies. Several analytical variables have been proposed to influence Hb measurements, but it is difficult to understand the impact on specific variables from large population or field studies. Therefore, we designed a highly controlled protocol that minimized most technical parameters to specifically investigate the impact of blood draw site and analytic device on Hb measurements. A diverse cohort of sixty healthy adults each provided a sequential capillary and venous blood sample that were measured for Hb using an automated hematology analyzer (ADVIA-2120) and two point-of-care devices (HemoCue 201+ and HemoCue 301). Comparing blood draw sites, the mean Hb content was 0.32-0.47 g/dL (2-4%) higher in capillary compared to venous blood from the same donors. Comparing different Hb measuring instruments, the mean Hb content was 0.19-0.46 g/dL (1-4%) higher measured with HemoCue devices compared to ADVIA-2120 in both capillary and venous blood from the same donors. The maximum variance in measurement was also higher with HemoCue devices using blood from venous (5-6% CV) and capillary (21-25% CV) sites compared to ADVIA-2120 (0.6-2% CV). Other variables including blood collection tube manufacturer did not affect mean Hb content. These results demonstrate that even when most technical variables are minimized, the blood draw site and the analytical device can have a small but statistically significant effect on the mean and dispersion of Hb measurements. Even in this study, the few participants identified as mildly anemic using venous blood measured by ADVIA-2120 would not have been classified as anemic using their capillary blood samples or point-of-care analyzers. Thus, caution is warranted when comparing Hb values between studies having differences in blood draw site and Hb measuring device. Future anemia testing should maintain consistency in these analytical variables.

Associations between type of blood collection, analytical approach, mean haemoglobin and anaemia prevalence in population-based surveys: A systematic review and meta-analysis

“…When examining the haemoglobin results from multiple comparison studies, Rappaport et al [ 8 ] found that haemoglobin concentrations in venous blood from the HemoCue® Hb 301 were generally higher than an automated haematology analyser used as a reference. Similarly, two studies found that, on average, the haemoglobin measurements from the HemoCue® Hb 301 were 3.4 g/L [ 16 ] and 2.6 g/L [ 15 ] higher than the HemoCue® Hb 201+. Whitehead et al [ 16 ] also tested the delayed reading of haemoglobin concentrations in both the HemoCue® Hb 201+ and 301 devices, and found a positive association between haemoglobin concentration and increased reading time (ie, time between aspirating the sample into the Hemocuvette and the reading taken on the device) only in the HemoCue® Hb 301 device.…”

“…Despite some contrary findings [12,13], the majority of studies have found that single drop capillary blood samples yield lower mean haemoglobin concentrations compared to venous blood [8,11,14]. One study found higher haemoglobin in pooled capillary blood than in venous blood [15], and a systematic review from 2019 found higher haemoglobin concentrations in single-drop capillary blood samples compared to venous blood samples among studies that used the same analytical methods [14]. Other studies have compared haemoglobin results from different point-of-care devices frequently used by population-based surveys.…”

“…Despite some contrary findings [ 12 , 13 ], the majority of studies have found that single drop capillary blood samples yield lower mean haemoglobin concentrations compared to venous blood [ 8 , 11 , 14 ]. One study found higher haemoglobin in pooled capillary blood than in venous blood [ 15 ]. Other studies have compared haemoglobin results from different point-of-care devices frequently used by population-based surveys.…”

“…Other studies have compared haemoglobin results from different point-of-care devices frequently used by population-based surveys. Studies suggest that the HemoCue® Hb 301 produces higher haemoglobin concentrations compared to the HemoCue® Hb 201+ device [ 8 , 15 , 16 ].…”

Pre-analytical variables influence zinc measurement in blood samples

“…If more than 0.5ml was collected, multiple capillary BCTs would be used up to 2ml total volume. Using this fingerstick protocol, 1-2 ml of capillary blood was collected from most participants [Killilea 2022]. Once the capillary blood was collected in all BCTs, tubes were inverted 4-6 times according to manufacturer's instructions and placed on ice while venous blood collection was completed.…”