Drop-to-drop variation in the cellular components of fingerprick blood: implications for point-of-care diagnostic development.
Author(s): Bond MM, Richards-Kortum RR
Publication: Am J Clin Pathol, 2015, Vol. 144, Page 885-94
PubMed ID: 26572995 PubMed Review Paper? No
Purpose of Paper
This paper investigated the variability in hemoglobin (Hb), white blood cell (WBC) count, differential WBC count, and platelet count between successive drops of fingerprick blood.
Conclusion of Paper
The variability in measurement between successive drops of fingerprick blood on a hematology analyzer was 2.3 to 3.4-fold higher for Hb, 3.9 to 5.7-fold higher for total WBC counts and 4-fold higher for platelet counts than in comparable volumes of venous blood. Similarly, the variability in hemoglobin between successive drops of fingerprick blood when analyzed by a point of care (POC) device was 2.5 to 5-fold higher than that in venous blood. The average coefficient of variance (CV) of the WBC, lymphocyte, and granulocyte counts in successive drops of fingerprick blood were 3.9 to 5.7, 1.4 to 3.0 and 3.2 to 7.7-fold higher (respectively) than for venous blood. Generally, average levels were within the variability of the instrument when three or more drops were considered for hemoglobin or five or more drops for white blood cell counts. Platelet counts were lower in fingerprick blood specimens than in venous blood specimens.
Studies
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Study Purpose
This study investigated the variability in the measurement of hemoglobin, total WBC count, differential WBC count, and platelet count in successive drops of fingerprick blood compared to venous blood and compared the variability in Hb measurement in specimens analyzed by hematology analyzer and a POC device. Single drops of capillary blood from healthy patients were collected in 20-μL MicroSafe capillary tubes (11 patients) and HemoCue disposable cuvettes (7 patients). To investigate if the variability was due to the volumes, venous blood from healthy individuals was diluted with plasma to obtain varying degrees of anemia, drawn into MicroSafe capillary tubes and HemoCue disposable cuvettes and analyzed. Only freely collected blood drops were analyzed.
Summary of Findings:
The variability in Hb measurement in successive drops of fingerprick blood using a hematology analyzer was 2.3-3.4 times higher than for comparable volumes of a single venipuncture specimen, but while differences of more than 1.6 g/dL were noted, there was no trend in levels with successive collection and the variability was dependent on the donor. Similarly, the drop-to-drop variation in Hb levels measured in the same venous specimen with the POC device was within the accuracy reported for the instrument, but the variability in Hb between successive drops of fingerprick blood was 2.5 to 5-fold higher than that in venous blood. Measured Hb levels were within the instruments variability, when the hematology analyzer measurements of three or more drops of fingerprick blood were averaged or when the POC measurements of nine or more drops were averaged. For 9 of 11 individuals the running average Hb levels as measured by hematology analyzer was within 1.1 g/dL of the venous levels when two or more drops were averaged, but for the remaining two individuals the running average Hb level remained more than 1.1 g/dL below the venous levels even after the levels from six drops were averaged. When the WBC counts for five or more drops were averaged, the level was within the instruments variability (0.3 106 cells/µL, respectively) of the level when six drops were averaged. For 10 of 11 individuals, the running average WBC was within the instrument variability of the venous levels when four or more drops were averaged, but for the remaining individual the running average remained lower even when six drops were averaged. Although the percentage CV of the monocyte and granulocyte counts for small volumes of venous blood fell within the reported variability for the instrument, the lymphocyte count showed a higher CV than the variability reported for the instrument. The average CV of the WBC, lymphocyte, and granulocyte counts in successive drops of fingerprick blood were 3.9 to 5.7, 1.4 to 3.0 and 3.2 to 7.7-fold higher (respectively) than for venous blood. The variability in platelet counts between successive drops of fingerprick blood was 4-fold higher than for venous blood specimens. When the platelet count in six drops of fingerprick blood was averaged for each patient, only 5 of 11 patients had average levels within the variability of the instrument. Fingerprick platelet counts were lower than venous platelet counts.
Biospecimens
Preservative Types
- None (Fresh)
Diagnoses:
- Normal
Platform:
Analyte Technology Platform Protein Hematology/ auto analyzer Cell count/volume Hematology/ auto analyzer Pre-analytical Factors:
Classification Pre-analytical Factor Value(s) Biospecimen Acquisition Method of fluid acquisition Venipuncture
Finger/heel prick sampling
Biospecimen Aliquots and Components Aliquot size/volume 1 drop
2 drops
3 drops
4 drops
5 drops
6 drops
7 drops
8 drops
9 drops
10 drops
Biospecimen Aliquots and Components Biospecimen heterogeneity Multiple specimens analyzed