Changes in full blood count parameters with age and sex: results of a survey of 900,000 patient samples from primary care

The Full blood count (FBC) is a frequently requested blood test in both primary and secondary care. Given that the population in England is ageing, with 18·3% of the population aged =65 years in 2018,1 it is important to ascertain how FBC parameters change in older patients. The aim of this study was to examine changes in FBC parameters with age and sex using a dataset of almost 900 000 primary care patients in England. Methods The reporting of routine blood tests in primary care for NHS England occurs electronically via the NHS spine data transfer service (DTS).2 In July 2013, all blood test results were captured from the DTS over a 23-day period as part of an audit of data quality, sponsored by the UK Department of Health and overseen by the Royal College of Pathologists. Anonymised FBC data were made available for analysis in accordance with NHS coding standards. The data were restricted to patients aged 1–100 years; results where sex was not specified or values were absent were excluded. Where values were identified as missing for haemoglobin, red blood cell count (RBC) or mean corpuscular volume (MCV), the data for that patient were excluded. Parameters were analysed by years of life and sex. Haemoglobin was analysed for a subgroup of adult patients identified to have ferritin, B12, folate and creatinine results within their respective reference intervals. The means were graphed to identify trends in the selected parameters. Results Haemoglobin For haemoglobin, 339 322 results for males and 535 716 results for females were included. In males, mean haemoglobin concentration increases from birth until approximately age 20 years. After this, it declines steadily until approximately age 70, when it starts to decline at an increasing rate (Fig 1A). In females, mean haemoglobin concentration increases until approximately age 14, when it starts to decline slowly until age 30, then increases again until age 60, and thereafter declining with age. Haemoglobin concentration in males and females begins to converge after age 60 and equalises by approximately 90 years.