We read with interest the use of blood gas analysis for estimation of haemoglobin concentration compared with laboratory measurement performed by Lucy et al at the Royal Hallamshire Hospital (1).

In the neonatal unit in Homerton University Hospital, we record the haematocrit in the observation charts. The measurements of haematocrit used are from blood gas results obtained from the Radiometer ABL 700 series blood gas analyser. We took 20 paired heel prick capillary blood samples from 10 babies for both laboratory full blood count and on site blood gas analysis inclusive of haematocrit over the course of a week as part of routine care. The gestational ages of the babies ranged form 26 to 32 weeks and their ages ranged from 1 to 44 days. The birth weight of the babies ranged from 0.73kg to 1.83kg. The median laboratory haemoglobin concentration was 13.8 g/dl (range 10.7-20.5 g/dl). The median packed cell volume(PCV) on blood gas analysis was 43.4% (range 34.4 -66.5%).

We found good correlation of blood gas analysis PCV to laboratory haemoglobin concentration(See Chart 1). The ratio of PCV to laboratory haemoglobin concentration was 3.1 with a correlation of 0.98. Herzog et al previously described a ratio of 3 (2).

Discussion

On the neonatal unit in Homerton University Hospital; blood gas analysis of haematocrit gives useful correlation to laboratory haemoglobin concentration with a ratio of 3.1. Blood gas analysis values are recorded on nursing observation charts with lactate, glucose and bilirubin. Nursing and medical staff are able to use the haematocrit as part of the clinical picture to decide when to transfuse critically ill babies or babies with sudden gastrointestinal, pulmonary or intraventricular haemorrhage.

S Tang, S Fang Neonatal Unit, Homerton University Hospital, Homerton Row, London E9 6SR

References

(1) Hinds L, Brown C, Clark S. Point of care estimation of haemoglobin in neonates. Arch Dis Child Fetal Neonatal Ed 2007;92:378-380

(2) Herzog B, Felton B. Haemoglobin screening for normal newborns. J Perinatol 1994;14(4):285-289

Dear Editor,

We read with interest the article by Hinds et al [1] comparing laboratory and blood gas analyser haemoglobin on their NICU. They found a good correlation between laboratory measures and the ABL725 Radiometer blood gas analyser in 127 babies on their unit. However, we feel that the focus of their article was somewhat limited, as they assessed haemoglobin and haematocrit alone. Blood gas analysers have become more sophisticated and are now able to perform many different analyses on a single blood sample including: electrolytes, calcium, glucose, lactate and bilirubin measurement.

We recently assessed the performance of the Roche OMNI-S blood gas analyser, with point of care (POC) systems in use on our NICU including: Ascensia Elite XL Blood Glucometers, bilimeters and hematocrit readers against laboratory tests, across a wide range of haematological markers [2]. This particular gas analyser has been rigorously assessed over a number of years [3,4]. An excellent correlation between the existing POC systems, laboratory and blood gas analyser measurements was demonstrated, not only with regard to haematocrit (correlation 0.85), but also bilirubin, sodium and potassium (correlations of 0.98, 0.83 and 0.80 respectively). We found a similar accuracy of haematocrit levels in our study (the maximum difference between measurements was 15%) compared to Hinds et al.

The OMNI-S gas analyser was also assessed against the Ascensia Elite XL portable glucometer with regard to serum glucose measures, as we frequently seemed to duplicate these measures on our unit. The gas analyser performed well over a wide range of glucose levels (up to 300 mg/dL; correlation of 0.91), but, like Hinds et al., with respect to haematocrit, we also found that the spread of the difference in measurements appeared to increase at the higher and lower range of values, although this failed to reach statistical significance.

We therefore agree with the authors that each neonatal unit should review their blood gas analysis procedures with the aim of reducing blood sampling for laboratory assays. We feel that modern gas analyser systems can reduce and even replace conventional laboratory testing. This is particularly pertinent where only one test is required (e.g. glucose or bilirubin). We recommend caution at high and low ends of the measurement spectrum (e.g. low blood glucose measurements), where clinical importance would be sufficient to warrant confirmatory laboratory analysis. We have shown that point of care testing in our unit does not differ significantly from laboratory measurements across a wide range of values with well- validated quality control settings. The use of a single blood analysis system simplifies staff training, equipment maintenance, reduces running costs and the volumes of blood samples required.

Yours sincerely

O J Arthurs, A W Kelsall

Neonatal Intensive Care Unit, Rosie Hospital, Box 226, Addenbrooke’s Hospital, Cambridge University NHS Foundation Trust, Hills Road, Cambridge, CB2 2QQ. United Kingdom

References

1. Hinds LE et al., Point of care estimation of haemoglobin in neonates. Arch Dis Child Fetal Neonatal Ed 2007; 92: F378-F380

2. Arthurs OJ, et al., Point of care measurements on a Neonatal Intensive Care Unit using the OMNI-S gas analyzer. Point of Care: The Journal of Near-Patient Testing & Technology; 2007; 6: 112 – 117

3. Bewley B, Creed G, Goerlach-Graw et al. Multicenter study on the analytic performance of a new point of care blood gas analyzer and its use in critical testing. Point of Care 2004; 4:149-155.

4. Rolinski B, Okorodudu AO, Kost G et al. Evaluation of total bilirubin determination in neonatal whole blood samples by multiwavelength photometry on the Roche OMNI-S point of care analyzer. Point of Care 2005; 4:3-8.