Measurement of haemoglobin as a screening test in general practice

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

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.

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.

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.