A convention that has been adopted in medicine is to estimate haemoglobin (HB) concentration as a third of packed cell volume (PCV) or vice versa. The present research set out to determine whether a proportional relationship exists between PCV and Hb concentration in cattle blood samples, and to assess the validity of the convention of estimating Hb concentration as a third of PCV. A total of 440 cattle in Ghana from four breeds (Ndama, 110; West African Short Horn, 110; Zebu, 110 and Sanga, 110) were bled for haematological analysis, specifically packed cell volume, using the microhaematocrit technique and haemoglobin concentration using the cyanmethaemoglobin method. Means, standard deviations, standard errors of mean and 95% confidence intervals were calculated. Trendline analyses generated linear regression equations from scatterplots. For all the cattle, a significant and consistent relationship (

Determining blood parameters is helpful in assessing the health status of animals. Common diseases in the tropics may lead to anaemia, examples of which include: helminthosis/helminthiasis, trypanosomosis, and tick-burden and tick-borne infections such as babesiosis and anaplasmosis. Measurement of anaemia is said to give a reliable indication of the disease status and production performance of trypanosome-infected animals (Nwoha & Anene

A convention has been adopted in medical laboratory practice in estimating Hb concentration as a third of PCV or vice versa (Bain & Bates

The aims of the present study were: (1) to determine whether or not a proportional relationship exists between PCV and Hb concentration in cattle blood samples and (2) to assess the validity of the convention of estimating Hb concentration as a third of PCV. It was hoped that these would help to provide information that is relevant for fieldwork and clinical diagnosis.

A total of 440 cattle in Ghana from four breeds (Ndama, 110; West African Short Horn, 110; Zebu, 110 and Sanga, 110), that were randomly selected, were bled for haematological analysis as part of a larger study on trypanotolerance. Cattle less than 1 year old were classified as calves, those between 1 year and 3 years as young, and those older than 3 years were classified as adults.

Packed cell volume, which is a measure of the proportion of the volume of the whole blood that is occupied by red blood cells, was determined by the microhaematocrit centrifugation technique (Jain

Haemoglobin concentration was measured spectrophotometrically by the cyanmethaemoglobin method (Jain

Means, standard deviations (s.d.), standard errors (s.e.) of mean and 95% confidence intervals (95% CI) were calculated using standard formulae. Differences in the means of the determined and calculated Hb concentration values were tested using a two-tailed paired sample test in Microsoft Excel (Microsoft, USA).

Scatterplots were drawn using Microsoft Office Excel (version 2007, Microsoft, USA) matching determined Hb concentration with PCV, and determined Hb concentration with calculated Hb values (one third of PCV). Linear regression models were estimated to evaluate the relationship between PCV, determined Hb and calculated Hb values. Trendline analyses were used to generate the linear regression equations. To avoid the possibility of bias, separate regressions were performed on the basis of breed, age or sex. The significance of the correlation coefficient for the linear regression equations was tested using the formula suggested by Smillie (1966) and Varkevisser, Pathmanathan and Brownlee (

where

Bland and Altman (

Spearman’s rank correlation coefficient (_{s}) was calculated, in Microsoft Excel, for the relationship between determined Hb and calculated Hb concentration, and also between the absolute differences and averages for individual samples, the latter as recommended by Bland and Altman (

Haematological and linear regression parameters according to breed, sex and category of cattle.

Variable | Class | PCV (%) | Hb Determined (g/dL) | Hb Calculated (g/dL) | Regression of Determined Hb versus PCV | Regression of Determined Hb versus calculated Hb | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|

(x ± s.d.) | 95% CI | (x ± s.d.) | 95% CI | (x ± s.d.) | 95% CI | |||||||

Breed | Wash | 110 | 31.79 ± 5.60 | 30.74–32.84 | 11.79 ± 1.72 | 11.47–12.11 | 10.60 ± 1.58 | 10.30–10.90 | _{1} + 3.00 |
_{2} + 3.00 |
0.76 | 12.22 |

N’dama | 110 | 34.50 ± 4.37 | 33.68–35.32 | 12.83 ± 1.67 | 12.52–13.14 | 11.50 ± 1.46 | 11.23–11.77 | _{1} + 3.56 |
_{2} + 3.56 |
0.70 | 10.22 | |

Zebu | 110 | 30.30 ± 4.95 | 29.37–31.23 | 11.58 ± 1.96 | 11.21–11.95 | 10.10 ± 1.65 | 9.79–10.41 | _{1} + 3.52 |
_{2} + 3.52 |
0.67 | 9.45 | |

Sanga | 110 | 34.39 ± 4.78 | 33.50–35.28 | 12.44 ± 1.88 | 12.09–12.79 | 11.46 ± 1.59 | 11.16–11.76 | _{1} + 2.14 |
_{2} + 2.14 |
0.76 | 12.24 | |

Sex | Male | 174 | 32.17 ± 5.12 | 31.41–32.93 | 11.99 ± 1.92 | 11.70–12.28 | 10.72 ± 1.71 | 10.47–10.97 | _{1} + 3.33 |
_{2} + 3.33 |
0.72 | 13.56 |

Female | 266 | 33.12 ± 4.93 | 32.53–33.71 | 12.26 ± 1.83 | 12.04–12.48 | 11.04 ± 1.64 | 10.84–11.24 | _{1} + 2.96 |
_{2} + 2.96 |
0.76 | 18.73 | |

Category | Calves | 86 | 34.06 ± 5.76 | 32.84–35.28 | 12.42 ± 1.95 | 12.01–12.83 | 11.35 ± 1.92 | 10.94–11.76 | _{1} + 4.43 |
_{2} + 4.43 |
0.69 | 8.86 |

Young | 138 | 33.41 ± 5.00 | 32.58–34.24 | 12.40 ± 1.94 | 12.08–12.72 | 11.14 ± 1.66 | 10.86–11.42 | _{1} + 2.89 |
_{2} + 2.89 |
0.73 | 12.46 | |

Adult | 216 | 31.80 ± 4.54 | 31.19–32.41 | 11.89 ± 1.76 | 11.66–12.12 | 10.60 ± 1.51 | 10.40–10.80 | _{1}+ 2.43 |
_{2} + 2.43 |
0.77 | 17.53 | |

_{1} + 3.11 |
_{2} + 3.11 |

PCV, packed cell volume; s.d., standard deviation; CI, confidence interval; Hb, haemoglobin concentration; _{1}, PCV; _{2}, calculated Hb (i.e. PCV/3); g/dL, grams per decilitre;

The proportion of samples for which determined Hb concentration was higher than calculated Hb concentration was 86.1% (379/440) and was significant (

The mean (± s.d.) of differences between determined and calculated Hb concentration values was 1.24 ± 1.29 (range: -3.56–7.25; lower 95% limit of agreement was -1.28; upper 95% limit of agreement was 3.76). The mean (± s.d.) of differences between determined and corrected calculated Hb concentration values was 0.00 ± 1.25 (range: -4.61–5.63; lower 95% limit of agreement -2.46; upper 95% limit of agreement 2.46).

Spearman’s rank correlation coefficient for the relationship between determined Hb and calculated Hb concentrations, (_{s}_{s}

Scatterplot of determined haemoglobin concentration versus packed cell volume for all cattle.

Scatterplot of determined versus calculated haemoglobin concentrations for all cattle.

Scatterplot of difference against average of determined haemoglobin and calculated haemoglobin concentrations for all cattle.

Scatterplot of difference after correction against average of determined haemoglobin and corrected calculated haemoglobin concentrations for all cattle.

For all of the cattle, a significant and consistent relationship was found between Hb concentration and PCV (%). This was expressed as Hb concentration (g/dL) = 0.28 PCV + 3.11. When the Hb concentration was estimated as a third of PCV, the relationship was expressed as Hb concentration (g/dL) = 0.83 calculated Hb + 3.11 (

In a study on humans, Carneiro

Linear regression analysis was employed to determine whether the relationship between PCV and Hb concentration differed on the basis of breed, sex and age categories of the cattle. The individual slopes within breed, sex and age categories did not differ significantly, except possibly for calves. These results may imply that a simplified relationship of Hb (g/dL) = 0.3 PCV + 3 may provide a more reasonable and better estimate of Hb concentration from the PCV of cattle. In cattle, the convention of estimating the Hb concentration as a third of PCV would need modifying to be a third of PCV + 3.

The convention or standard of estimating Hb has been used extensively in medicine to estimate the prevalence of anaemia (Carneiro

The relationship between PCV and Hb is expressed in the Mean Corpuscular Haemoglobin Concentration (MCHC) (Quinto

In conclusion, a simplified relationship of Hb (g/dL) = (0.3 PCV) + 3 may provide a better estimate of Hb concentration from the PCV of cattle. It is, therefore, recommended that if it is necessary to estimate Hb concentration from PCV value, then the simplified relationship may be more appropriate to use.

Thanks to Jerry Oddoye and Abdulai Munkaila of the Veterinary Investigation Laboratories of the Veterinary Services Directorate Ghana for their technical assistance. The help received from the managers of the cattle herds at sampling sites is appreciated.

The authors declare that they have no financial or personal relationship(s) that may have inappropriately influenced them in writing this article.

P-K.T. (University of Cape Coast) developed the concept, analysed data and wrote the article. E.Y.G. (University of Cape Coast) was involved in the collection of field samples, analysis of samples and contributed to the write up and review of the article.