Dr Theresa Saklatvala
The complete blood count (CBC) is one of the tests most frequently used by clinicians. Its three main components – haemoglobin (Hb), white blood cell (WBC) and platelet count – are indicative of a range of pathological states, including the following:(1)
– Abnormal bone marrow pathology may be indicated by an increased or decreased total WBC. The presence of microbial or viral infection may be inferred from leucocytosis with an associated neutrophilia or lymphocytosis. A decrease in WBC might be indicative of a chemotoxic effect during chemotherapy.
– A decrease in red blood cell count and/or Hb may infer anaemia, and possibly the aetiology of the anaemia. Monitoring of the treatment of anaemia, and determining the amount of blood required for transfusion, are made possible by measuring the rate of increase of Hb.
– Measuring of platelet size is useful in determining the thrombopoetic activity of bone marrow, and an increase or decrease in platelet numbers can indicate disorders of haemostasis.
A trend within diagnostic testing is that more tests are becoming available at point of care. The need for such testing will increase as the practice of medicine continues to evolve, and as individuals take more responsibility for their healthcare. The benefits of point-of-care testing include better clinical decision making, better patient compliance and better patient satisfaction. The drivers include the following:(2)
- Integration of test results into clinical flow, allowing for simultaneous diagnosis and intervention
- Just-in-time delivery of test results, enabling a high-quality clinical response
- Lower likelihood of medical errors, as there is less demand for transcription and transfer of test results
- Reduction of test errors due to sample handling, labeling and processing
- May lead to cost savings against laboratory testing, when all costs are taken into account
- More frequent testing made more acceptable to patients, as smaller test samples are taken
- Improved safety resulting from reduced blood sample handling
- Mobility and ease of deployment
Focus on haematology
The time-honoured haematology laboratory tests of proven clinical usefulness are CBC, leucocyte differential count and reticulocyte count.
Manual methods are being supplanted by automated technology, and simultaneous laboratory computerisation has revolutionised the way results are reported and transmitted to clinicians. The result has meant longer and more complicated reporting of these three parameters. Why have the reports become so complex? Contributing factors include:
– the tradition of laboratory haematology
– the addition of more parameters produced by automated analyses
– the belief that more is better
This plethora of data has made it more difficult for physicians to focus on what is useful for the most timely management of their patients, and it is conceivable that their comprehension of essential data is impaired.
The purpose of a survey of more than 2000 physicians conducted by Sandhaus and Meyer(3) was to establish what laboratory data from the variety of components of the CBC count were of most frequent clinical use.
In their study, they concluded that 90% of physicians use only four of the 11 parameters routinely reported in the CBC count: haemoglobin, haematocrit, WBC count and platelet count. There were two exceptions: paediatricians found more parameters to be of clinical usefulness, and primary care physicians looked at mean cell volume for the evaluation of anaemia (see Table 1).
So with most of the data typically reported in a routine CBC/differential count report not used by a substantial proportion of physicians, one must raise questions about the overall usefulness and cost-effectiveness of full-blown, all-inclusive laboratory reports, and about the design and implementation of new laboratory haematology instrumentation that result in the most timely and effective communication of laboratory information to clinicians.
If clinicians find diagnostic benefit in having a complete CBC report, they must have it. To that end, Sandhaus and Meyer suggest that perhaps modifying the format in which data are provided so as to give prominence to the most useful parameters might result in more efficient uptake of what a clinician must know, quickly.
When considering the design and implementation of new laboratory haematology instrumentation, there is a balance to be struck between quantity of data and useability. Extensive medical education and abundant literature do not guarantee that physicians will interpret and use the data just because it is there.
To reduce the argument to the level of the individual patient, and particularly if you place that patient in a point-of-care environment, laboratory data must be interpreted in the context of its usefulness to that patient. Just because a parameter is available does not mean that it should be reported routinely. More occasionally used parameters, which are still useful to albeit a minority of patients, should obviously continue to be made available to clinicians.
In summary, Sandhaus and Meyer found not only that much of the data in a CBC/differential count are not used, but that an over-abundance of data that are not used by physicians might actually impede perception and comprehension of what is essential, and contribute to errors in medical judgement (Box 1).
There then remained the issue of what was the minimum number of parameters that could be measured at point of care without missing the diagnosis of any clinically significant condition.
Hb and WBC count in combination
A study by Osei-Bimpong and colleagues recently published in the International Journal of Laboratory Hematology describes results where the CBC assessment correlates with the screening for white blood cell and haemoglobin in combination.(1) They collected CBC data from 2191 patients over the course of five weeks, comprised of 42.6% women and 57.4% men, with an age range of 16-91 years. The study cohort was a randomised selection who had the test requested by their clinician in the Hammersmith Hospital Imperial College Healthcare Trust as an adjunct for the investigation of the underlying conditions. Thirty-nine percent of the patients were referred from general practitioners and 33% were hospitalised inpatients: the remainder were from outpatient departments.
All samples were taken in the morning and standard laboratory protocol was followed.
CBC profiles were divided into two groups: one in which the white cell count and haemoglobin were within normal reference range, and one in which they were beyond the normal reference range.
All profiles of the abnormal group had blood films prepared and examined microscopically for morphological features and cell counts to verify CBC. The degree of abnormality was categorised using the ‘plus’ grating scale.
Nine hundred and thirty-nine CBC profiles were in the normal group, where both WBC and haemoglobin were within the normal range. And in this group, there were 841 samples (89.6%) in which the other CBC parameters were within the normal range. There was an abnormal CBC parameter in only 98 cases out of 939. In the minority of cases where the WBC and haemoglobin were normal, the CBC could have one or more parameters outside the reference range, but the degree was remarkably subtle and of little clinical significance.
Of the cohort of 2191, 1252 CBC profiles were abnormal, in other words, either or both WBC and haemoglobin fell outside reference limits. In every case, there was an additional CBC parameter outside the reference limit. Not one of the 1252 samples had a normal value for the rest of the CBC parameters.
To summarise their results, all CBC parameter ranges were closer to the corresponding reference range in the normal group than in the abnormal group:
- Within the normal group, the WBC differential was normal in most cases, and the data range for each white cell type was narrower in comparison with the abnormal group. A statistically insignificant number of patients in the normal group had abnormal neutrophil counts, which may have been attributable in part to the fact that approximately 25–50% of persons of African origin have abnormally low neutrophil counts.
- Within the normal group, the erythrocyte indices were also within the normal reference limit. Red blood cell count was beyond the reference limit in only 0.6% of cases (compared to 39% of patients in the abnormal group).
- In only 2.2% of samples with a normal WBC and haemoglobin was the platelet count outside the normal reference range (compared to 29.1% of cases where the WBC and/or haemoglobin was abnormal). The degree of abnormality was remarkably subtle.
This reported use of white cell count and haemoglobin in combination as a cost-effective and rapid-response screen for the prediction of CBC normality represents a significant contribution to the diagnosis and treatment of a range of debilitating diseases.
A later study by Munoz and colleagues(5) of 247 primary care patients to determine if there was any statistically significant difference in haemoglobin values obtained through any of three methods: routine laboratory tests (capillary and venous), capillary blood analysis, and venous blood analysis. There was none. The obvious conclusion was that haematology testing at point of care should be used in the interest of saving material and human resources.
Point-of-care testing is becoming an important adjunct to haematology laboratory practice (Box 1), in hospital out patient and critical care departments as well as for diagnostic testing at primary care centre clinics or in general practice. Development of diagnostic systems that quickly and simply yield accurate assessment of CBC through combined Hb and WBC measurement result in better clinical decision making, better patient compliance and better patient satisfaction (Box 2).
Box 1: Key features of point-of-care systems for lab-accurate results of haemoglobin and white blood cell count
Point-of-care white blood cell count
- For use for quantitative determination of white blood cells (WBC) count in capillary or venous whole blood
- Result presented within minutes on analyser’s display
- Fully automated system requiring neither intervention of operator nor manipulation of the specimen or reagent
- Operation requires no specific training
- When analysis has been performed, results are shown in numerical figures, requiring no further interpretation or calibration
Point-of-care haemoglobin systems
- Designed for quantitative point-of-care whole blood haemoglobin determination in capillary or venous blood
- Results displayed within 10–60 seconds (depending on system)
- Fully automated system requiring neither intervention of operator nor manipulation of the specimen or reagent
- A swift and effective tool for anaemia screening
Box 2: Summary of results key to development of point-of-care CBC determination
- Much of the data in a CBC/differential count are not used.
More than 90 percent of physicians use only four of the 11 parameters reported in the CBC: haemoglobin, haematocrit, platelet count and WBC count
Sandhaus LM and Meyer P How useful are CBC and reticulocyte reports to clinicians?
American Journal of Clinical Pathology 2002; 118: 787-93.
- Haematology testing at the point-of-care saves material and human resources.
Sending a large proportion of blood samples to reference laboratories for CBC represents a waste of material and human resources, as the larger part of these samples show normal haemoglobin values.
Munoz M et al. Utility of point-of care haemoglobin measurement in the HemoCue-B haemoglobin for the initial diagnosis of anaemia Clinical Laboratory Haematology 2005; 27:99-104
- Complete CBC is not always necessary.(4)
Only patients with a low haemoglobin value need follow-up with a CBC. Point-of-care testing is available for lab- accurate Hb and WBC, which can provide the benefits stated in the article.
Lewis SM and Osei-Bimpong A Haemoglobinometry in general practice 2003; 25: 343-46
- In the majority of cases where the WBC and the Haemoglobin are within the normal range, the remainder of the CBC profile is normal as well.
Osei-Bimpong A et al. The use of the white cell count and haemoglobin in combination as an efficient screen to predict the normality of the full blood count International Journal of Laboratory Hematology 2011; accepted for publication
- Osei-Bimpong A et al. The use of the white cell count and haemoglobin in combination as an effective screen to predict the normality of the full blood count International Journal of Laboratory Hematology 2011; accepted for publication
- Global drivers of point-of-care testing Clinica 2010 March:32-35.
- Sandhaus LM and Meyer P How useful are CBC and reticulocyte reports to clinicians? American Journal of Clinical Pathology 2002; 118: 787-93.
- Lewis SM and Osei-Bimpong A Haemoglobinometry in general practice 2003; 25: 343-46.
- Munoz M et al. Utility of point-of care haemoglobin measurement in the HemoCue-B haemoglobin for the initial diagnosis of anaemia Clinical Laboratory Haematology 2005; 27: 99-104.