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SYNOPSIS A capillary blood collection technique which facilitates the estimation of routine haematological parameters, including platelet count and sedimentation rate, is described. The technique requires 05 ml of blood, allows closer reproducibility than pipette collection methods, is suitable for monitoring blood counts in patients receiving cytotoxic agents, and can be integrated with semiand fully-automated production lines.The ability to collect capillary blood from thumb or heel is essential in paediatric haematology. Capillary blood specimens for routine blood tests are usually collected into several individual pipettes and the appropriate dilutions made at the bedside (Brecher, Schneiderman, and Cronkite, 1953;Lewis and Benjamin, 1965;Dacie and Lewis, 1968;Brecher, 1971). This is time consuming and can be technically difficult, particularly when the child is in an incubator. When the specimens reach the laboratory they may require to be processed separately from the semi-and fully-automated production lines used for venous blood. A major disadvantage of pipette collection and dilution at the bedside is that additional tests cannot be performed, or an abnormal test result repeated, without a return visit to the patient.A simplified collection technique in which 0 5 ml of capillary blood is taken directly into a single plastic container is described. A micro-method for estimation of the erythrocyte sedimentation rate (ESR) on the same blood sample has been developed simultaneously.

In this laboratory, we have been using a method of quality control for our Coulter Model S which is not related to commercial whole blood standard preparations. In the national quality control trials, it has been found consistently that participants using Coulter S produce a lower mean value for haemoglobin than with other systems and, although the difference is in the order of 0-2-0-3 g/dl, 0.5 g/dl is just within 2 SD. Although there is no definite information, it seems likely that this discrepancy is due to the use of 4C as a calibrating material by the majority of Coulter S users, but not by others. A trial is now planned which will include calibrated whole blood, a cyanmethaemoglobin preparation, and the ICSH Intemational Reference Preparation in order to try to identify the cause of the discrepancy.

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Results and discussionAfter evaluation and comparison of many different methods, Sornas developed and recommended the sedimentation method for cytology of CSF (S6rnas, 1967; Aronson et al., 1974). The cytocentrifuge method has also been recommended recently by a few investigators (Drewinko et al., 1973; Evans et al., 1974). We have found much cell distortion with the cytocentrifuge method and very poor yields, as has been reported by others (Addiego and Woodruff, 1973). The distortion of cell morphology, especially the spreading of the cytoplasm, makes interpretation difficult (Fig. 1). Reduced distortion of cell morphology was well demonstrated in CSF from a patient with Chediak-Higashi's syndrome. Giant granules in the cytoplasm of lymphocytes were seldom seen in cytocentrifuge preparations but were well demonstrated in the preparations by our sedimentation method (Fig. 2).The method described here is also simpler and more practical. It is difficult to scrape off completely the petroleum jelly in the method of Sornas (1967), and this method has also been criticised as timeconsuming (Castleberry et al., 1975). Our method not only eliminates the procedure of applying and scraping off the petroleum jelly but also shortens the time considerably. Since the height of fluid within the circle was no more than 3 mm, the time required for cells to settle at the rate of 0-1 mm/min will be Conventional methods of quality control depend on the use of standards for machine calibration and the use of control samples to detect drift. The methods applied to haematology require the use of expensive whole blood reference preparations. Control samples, although they can be prepared daily or slightly less frequently (Hamilton and Davidson, 1973), must be interposed at frequent intervals between test samples. The control value can be affected by carry-over from the previous specimen (Brittin