Tier 2 project the reliability of pcv measurements

The Reliability of PCV Measurements

Sami Da Costa

Introduction• PCV measurements are done routinely in general

practice on a day to day basis.

• However, the operator reliability of PCV measurements within the profession has not been assessed.

• This raises the questions:- How reliable are PCV measurements?- Are PCV measurements the best method of

accessing red cells?

Hypothesis

Measuring PCV is unreliable

(Unreliable defined as a coefficient of variationof more than 5% in all animals in more than 5%of cases).

Method

• Samples could be stored for up to 5 days in the fridge (4oC)

• Samples were re-suspended for 5 minutes on the roller before capillary tubes were filled.

• 16 samples were used in this study over the course of a 3 week period

• 6 people obtained 2 PCV measurements for each sample by using the micro haematocrit reader

Protocols:• Breakage of the capillary tube during

preparation (x)

• Loss of blood from a capillary tube whilst in the microfuge (z)

• There were no breakages in the microfuge

• No students were injured

Materials

• Capillary tubes

• Plasticine

• Microfuge

• Micro haematocrit

reader

Data

b = ran out of sample

All breakages that occur during capilary tube preparation are marked with an x

All breakages that occur during spinning of capillary tubes are marked with a y

Loss of blood from a capillary tube whilst spinning is marked with a z

All injuries are marked with an i

Sample 1st reading 2nd reading Problems S.d Median CV%1st

reading2nd

reading Problems S.d Median CV%

235795 43.5 43.5 x 0.0 43.5 0.0% 42 43 zz 0.7 42.5 1.7%

243974 16 15 0.7 15.5 4.6% 13 13 0.0 13 0.0%

244456 46 46 0.0 46 0.0% 45 45 0.0 45 0.0%

246616 41 41 0.0 41 0.0% 39 39 0.0 39 0.0%

246661 62 64 1.4 63 2.2% 61 61 0.0 61 0.0%

246687 49 49 0.0 49 0.0% 49 49 0.0 49 0.0%

246725 55 56 0.7 55.5 1.3% 56 56 zz 0.0 56 0.0%

231492 51 52 0.7 51.5 1.4% 47 49 z 1.4 48 2.9%

244970 46 45 zz 0.7 45.5 1.6% 45 45 0.0 45 0.0%

245782 49 50 0.7 49.5 1.4% 39 39 0.0 39 0.0%

246408 40 42 1.4 41 3.4% 48 49 0.7 48.5 1.5%

216519 60 57 2.1 58.5 3.6% 50 50 0.0 50 0.0%

246189 47 49 z 1.4 48 2.9% 46 46 z 0.0 46 0.0%

246540 44 44 x 0.0 44 0.0% 43 43 0.0 43 0.0%

246683 56 54 1.4 55 2.6% 54 54 0.0 54 0.0%

231109 50 51 0.7 50.5 1.4% 52 52 zz 0.0 52.0 0.0%






Data


reading2nd


235795 44 43 0.7 43.5 1.6% 43 42 z 0.7 42.5 1.7%

243974 16 16 0.0 16.0 0.0% 16 16 0.0 16.0 0.0%

244456 46 46 0.0 46.0 0.0% 46 46 0.0 46.0 0.0%

246616 39 39 0.0 39.0 0.0% 38 38 0.0 38.0 0.0%

246661 66 64.5 1.1 65.3 1.6% 61 61 0.0 61.0 0.0%

246687 51 51 0.0 51.0 0.0% 48 48.5 0.4 48.3 0.7%

246725 56 56 zz 0.0 56.0 0.0% 56 56 zz 0.0 56.0 0.0%

231492 47 47 zzzzz 0.0 47.0 0.0% 54 51 zz 2.1 52.5 4.0%

244970 45 45 z 0.0 45.0 0.0% 46 45 z 0.7 45.5 1.6%

245782 39 39 0.0 39.0 0.0% 38 39 z 0.7 38.5 1.8%

246408 48 48 0.0 48.0 0.0% 48 47 0.7 47.5 1.5%

216519 50 50 zzzzz 0.0 50.0 0.0% 53 zzzzb

246189 47 47 0.0 47.0 0.0% b

246540 44 44 0.0 44.0 0.0% b

246683 54 54 0.0 54.0 0.0% 56 zzzzzb

231109 51 zzzb zzzzb






Data


reading2nd


235795 43 42 0.7 42.5 1.7% 43 43 0.0 43.0 0.0%

243974 18 16 1.4 17.0 8.3% 11 11 0.0 11.0 0.0%

244456 47 46 0.7 46.5 1.5% 45 45 0.0 45.0 0.0%

246616 38 38 0.0 38.0 0.0% 38 38 0.0 38.0 0.0%

246661 62 62 0.0 62.0 0.0% 62 62 0.0 62.0 0.0%

246687 50 50 0.0 50.0 0.0% 49 49 0.0 49.0 0.0%

246725 56 56 z 0.0 56.0 0.0% 56 57 0.7 56.5 1.3%

231492 49 52.5 z 2.5 50.8 4.9% b

244970 47 48 z 0.7 47.5 1.5% b

245782 38 37.5 0.4 37.8 0.9% b

246408 47 47 0.0 47.0 0.0% b

216519 53 zb b

246189 b b

246540 b b

246683 56 zz b

231109 b b

Comparing inter-student medians

Sample no. S.d Median CV%Number of

readings

235795 0.5 42.8 1.1% 6

243974 2.3 15.8 14.4% 6

244456 0.6 46.0 1.3% 6

246616 1.2 38.5 3.0% 6

246661 1.6 62.0 2.6% 6

246687 1.0 49.0 2.0% 6

246725 0.3 56.0 0.6% 6

231492 2.3 50.8 4.6% 5

244970 1.0 45.5 2.3% 5

245782 4.9 39.0 12.6% 5

246408 3.1 47.5 6.5% 5

216519 4.9 50.0 9.8% 3

246189 1.0 47.0 2.1% 3

246540 0.6 44.0 1.3% 3

246683 0.6 54.0 1.1% 3

231109 1.1 51.3 2.1% 2

Median CV% 2.2%

Interpretation of ResultsDescriptive statistics• 210 capillary tubes used in total

• 2/210 breakages during capillary tube preparation

• 53/210 lost blood in the microfuge (25%!)

• 9 of the 16 samples were depleted before 6 people could measure the PCV

Mathematical Statistics

• Median CV%: 2.2%

(Intra-student variation)

• Range of CV%: 0.6-14.4%

(Inter-student variation)

Discussion

• In this study: 4/16 (25%) had a coefficient of variation ≥ 5%

• Therefore, in this study the hypothesis is correct – measuring PCV is unreliable by our previous definition

Limitations of study

1. Samples ran out

2. Reliability of this study could be improved by including more samples and running the study for a longer period of time.

(This was a short study and included 16 samples collected over a 3 week period)

Conclusions

• Measuring PCV is unreliable by our definition

Future studies

• Comparative studies

(e.g. Haematocrit [Idexx] or haemoglobin)

References• Bull, B.S. (2001) Is the Packed Cell Volume (PCV) Reliable?

Laboratory Hematology. [Online] Carden Jennings Publishing. Volume 7 (Number 4/December). p.191. Available from: http://cardenjennings.metapress.com/app/home/contribution.asp?referrer=parent&backto=issue,5,14;journal,51,57;linkingpublicationresults,1:104952,1

• Stott, R.A.W. Hortin, G.L. Wilhite, T.R. Miller, S.B. Smith, C.H. Landt, M. (1995) Analytical Artifacts in HematocritMeasurements by Whole-Blood Chemistry Analyzers. Clinical Chemistry. [Online] Volume 41 (Number 2/February). P.306. Available from: http://www.clinchem.org/content/41/2/306.abstract

http://cardenjennings.metapress.com/app/home/contribution.asp?referrer=parent&backto=issue,5,14;journal,51,57;linkingpublicationresults,1:104952,1

http://www.clinchem.org/content/41/2/306.abstract

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