The use of the white cell count and haemoglobin in combination as an effective screen to predict the normality of the full blood count

INTRODUCTION

The utility of the full blood count (FBC) is vast with each parameter serving as a tool to aid diagnosis and monitor disease progression. However, the effectiveness of the test is hampered because of increased workload and lack of interpretation. In the effort to redress this issue, the combined use of the white blood cell count (WBC) and haemoglobin in predicting the normality of the FBC is evaluated.

METHOD

FBC data were collated from 2191 patients and classified into two groups depending on whether the WBC and the haemoglobin were within the reference range. Blood films were examined on the abnormal FBC samples in each group and graded on morphology.

RESULTS

The FBC was normal in 89.6% of cases in the presence of a normal WBC and haemoglobin with subtle abnormalities in the remainder; 1+ grading of abnormal morphology in 93%. However, when the WBC and/or haemoglobin was abnormal, the remaining FBC was significantly abnormal (P < 0.05) and the corresponding blood films were grossly abnormal; 2+/3+ grading in 96% of cases.

CONCLUSION

We concluded that in the presence of a normal WBC and haemoglobin, the FBC is normal in almost all cases and measuring these two parameters could be used as an effective screen to predict FBC normality.

Point-of-care method for total white cell count: an evaluation of the HemoCue WBC device

Point-of-care testing (POCT) is becoming an important adjunct to haematology laboratory practice. An important component of the blood count is the total white cell count (WBC). Previously, this required laborious microscopic cell counting, but it can now be performed by means of automation; however, in many under-resourced countries, costly automated counters are only available in very few central hospitals. Moreover, neither method is practical in most POCT situations. The HemoCue WBC has been developed as a simplified alternative method, consisting of a reagent pre-loaded disposable cuvette together with basic image analysis technology. This report describes an assessment of its utility. The WBC of 500 routine blood samples from the hospital were tested in parallel by the HemoCue WBC and by a reference analyser to assess accuracy and utility of the former. The tests included precision, linearity, type of blood sample and anticoagulant and potential interfering substances in blood specimens. In the tests for accuracy, 192 of the 200 showed percentage difference from the NEQAS reference of <10% whilst the remaining eight samples differed by <12%, thus meeting the requirements of Clinical laboratory improvement amendments (CLIA)-88 regulations. Of the samples tested with potential interfering substances only those with >2% normoblasts or reticulocytosis showed significant differences from the reference measurements. The HemoCue WBC is reliable for WBC counts within the analytical range of 0.4-30.0 x 10(9)/l, except in samples where there are significant numbers of normoblasts or reticulocytes. It is simple to use and provides a valuable advance in the facilities available for POCT in haematology.

Evaluation of the utility of the HemoCue 301 haemoglobinometer for blood donor screening

BACKGROUND AND OBJECTIVES

Reliable blood donor screening requires more accurate measure of haemoglobin (Hb) than by either copper sulphate or the haemoglobin colour scale. The HemoCue haemoglobinometer has established a method for this, but it is considerably more expensive; a modified version (HemoCue 301) has now been developed with a cheaper reagent-free cuvette for use in budget-restricted situations. This report describes evaluation of the performance, the assessment of reproducibility and accuracy of this modified analyser against the reference technique for Hb measurement.

MATERIALS AND METHODS

Over 300 routine blood samples from specimens received routinely in a hospital laboratory were tested in accordance with the International Committee for Standardization in Haematology (ICSH) protocol. Accuracy and linearity were confirmed by the reference method with the WHO international haemoglobincyanide reference standard. Tests were also performed on selected samples for checking interference by biochemical abnormalities and leucocytosis. The effects of various sample storage conditions prior to testing were also tested.

RESULTS

Ninety per cent of results were within 4% of true values, 96% within 6% and in only three cases was the deviation > 10%, due to interference by bilirubinaemia and/or C-reactive protein. At an Hb value of 120 g/l for donor selection, there were no cases where the method would have been misleading.

CONCLUSION

HemoCue 301 provides a simple and reliable anaemia screen method, conforming to the requirements of CLIA'88 regulations; it is reliable for discriminating Hb values for donor acceptance. The main advantage is that the cuvettes are significantly cheaper than the previous models, and will not deteriorate in adverse climatic conditions.

ESR or CRP? A comparison of their clinical utility

OBJECTIVE

To review the normal reference values for erythrocyte sedimentation rate (ESR) and the significance of high values in the elderly, to re-examine the correlation, if any, between ESR and C-reactive protein (CRP) and to compare their utility and limitations for both health screening and clinical management of patients.

METHODS

CRP and ESR were measured in 295 blood samples from male and female subjects in whom their family doctors had found no clinically significant symptoms nor abnormal physical sign and in whom all other pathology tests gave normal results. None had been hospitalised during at least a six-week period prior to the study.

RESULTS

The results showed a mean ESR of 10 mm/1 h (range 0-25) in both males and females below the age of 40 yrs; this increased with age, to a mean of 18 mm (range 0-35) by 60 yrs in both men and women. In the CRP test, 95% of the samples in the >40 yrs group had CRP range of 0-18 mg/l compared with 0-10 mg/l in the younger subjects. The distribution plot of CRP results showed a left skew with mode at about 2 mg/l, whereas the equivalent ESR distribution shows a broad plateau with less skew. Thus, there was more overlapping of the numerical values for ESR and CRP in subjects younger than 40 yrs, as compared with those over 40 yrs old in whom the two sets of measurements were well separated. The relative utility of the two tests in clinical management of patients was also discussed. Different rates of increase and subsequent fall in the test results were shown over several weeks on a patient with an acute infection. Initially, both tests were increased, but after antibiotic therapy the CRP returned to normal indicating that remission had occurred, whereas the ESR remained high, indicating persistence of the infection. A subsequent dramatic increase in CRP to 180 mg/l confirmed the re-infection that had been indicated earlier by the ESR. After further antibiotic therapy CRP fell to normal, followed later by a slower reduction in ESR to a normal value for the patient's age.

CONCLUSION

This study confirms that after the age of 40, there is an age-related elevation of ESR, increasing steadily, especially after age 60 yrs. CRP is also affected by age, but to a much less extent. ESR and CRP appear to be equally useful and reliable as a screening test. Accordingly, in deciding which test should be carried out account must be taken of their relative convenience and cost. However, when required as a clinical test in the management of patients with specific diseases both tests should be carried out in tandem.

Measurement of haemoglobin as a screening test in general practice

OBJECTIVE

To assess the validity of using the measurement of haemoglobin as a primary screen test at point-of-care in general practice.

METHODS

1100 consecutive full blood counts carried out at Hammersmith Hospital haematology laboratory on blood samples sent by the general practitioners in the area were reviewed. Where haemoglobin was in the normal range all the parameters of a full blood count were checked and a blood film was screened in order to identify any abnormal features occurring in the absence of anaemia.

RESULTS

Haemoglobin was normal in 81% of the samples, and in 81% of this set none of the blood count components showed any abnormal features (i.e. outside two standard deviations of normal reference range). The remaining 19% of cases included 32 with iron deficiency, 26 with high MCV, 84 with leucocyte abnormalities (neutrophilia, neutropenia, lymphocytosis, eosinophilia, monocytosis) and 19 with platelet counts either too high or too low. The predictive value of a normal full blood count from a normal haemoglobin was 0.81. However, when the limits of normal reference values were set at three standard deviations only 7% of the cases showed abnormal features and the predictive value of normality from a normal haemoglobin increased to 0.92.

CONCLUSION

There are now simple and suitable devices available for measuring haemoglobin at point-of-care, away from a laboratory. This provides a useful screening test in general practice as a full blood count would, as a rule, be required only in the small proportion of cases where anaemia is detected or the patient's history and/or clinical signs specifically indicate the need for this further investigation. This approach should contribute to more efficient, convenient and economical practice without compromising clinical management.

Haemoglobinometry in general practice

Haemoglobinometry as a primary point-of-care test is well established. This study was undertaken to assess whether haemoglobinometry by itself provides an adequate haematological screening procedure in general practice. In a series of 500 sequential blood counts received by the central hospital laboratory from local doctors, 405 (81%) had a normal haemoglobin. Full blood counts on these samples showed 15% with one or more blood count parameters outside 2SD of normal reference values, including increased MCV, low MCV with low MCH and MCHC, leucocytosis with neutrophilia, a few cases with neutropenia, lymphopenia, monocytosis or eosinophilia. When the limits were set at 3SD, these abnormalities were found in only 7.6% of the cases. Calculation of test utility gave a positive predictive value of 0.83, a negative predictive value of 0.85, with a likelihood ratio of 14.3 and an overall diagnostic reliability of 84%. It was concluded that haemoglobin alone is a valuable primary screening test and a full blood count is required only when anaemia is present or when the patient's history and clinical signs indicate the need for such further investigation. Using this protocol it is unlikely that any serious error will be made in diagnosing a clinically significant condition; the main limitation is failure to diagnose pre-anaemic iron deficiency.