Biochemistry in dietetic practice: the cost of tests and do we really need them?
Biochemical tests are integral to modern dietetic practice. From assessing nutritional status to monitoring long-term disease management, they offer a window into our patients’ physiology. But with NHS resources stretched and the cost of testing rising, how do we decide what we really need - and when is “just checking” not justified?
The role of biochemistry in dietetics
For dietitians, blood results often guide key decisions - from diagnosing deficiencies to assessing metabolic control or evaluating treatment efficacy. Whether monitoring electrolytes during refeeding, checking HbA1c in diabetes, or reviewing urea and creatinine in renal disease, biochemistry underpins evidence-based practice.
However, each test ordered carries both a cost and a consequence. Laboratory assays vary in price, but even common panels like Urea and Electrolytes (U&Es), Liver Function Tests (LFTs), and C-reactive protein (CRP) cost several pounds per patient. When multiplied across thousands of requests, unnecessary testing can have a significant financial and environmental impact.
There is now more focus on preventative care, and First Contact Practitioners in the community treat patients as early as possible, i.e., in the GP practice, and reduce the strain on secondary care.[8] The Network Contract DES Additional Roles Reimbursement Scheme has provided funding to primary care to create 26,000 additional roles in 2023-2024. Such roles include: First Contact Physiotherapists, First Contact Dietitians, Occupational Therapists, Podiatrists, and Paramedics.[8] The focus of these First Contact Practitioners is treating people within primary care and helping people to remain independent, where possible, return to work, and try to prevent hospital admission or the need for secondary care referrals.[1,6,8,9]
First Contact Dietitians (FCDs) can reduce frailty and disease risk by identifying and treating malnutrition in primary care.[3] FCDs aim to:
Diagnose malnutrition earlier
Optimise nutrition management
Reduce GP consultations
Reduce referrals to secondary care
These services have led to major cost savings for primary care, with one example service reporting a cost saving of £15,379 made by having a primary care network (PCN) dietitian reviewing oral nutritional supplement use.[3]
FCDs and PCN dietitians can also work in specialist areas within primary care, such as diabetes, IBS, or weight loss management, and can also help get people into treatment faster instead of waiting for a secondary care appointment, which could have a long waiting list.[3]
Testing in the NHS: balancing cost and clinical value
Within the NHS, pathology budgets are under increasing scrutiny. Clinical biochemistry departments process millions of samples each year, with automation improving efficiency but not eliminating cost. Each sample involves reagents, technician time, reporting, and waste disposal - not to mention the logistics of transport and storage.
NHS England’s Getting It Right First Time (GIRFT) initiative has reported substantial variation in biochemistry test requesting between trusts, particularly for assays such as vitamin D and thyroid function tests. (6, 7) The goal is not to discourage testing, but to promote thoughtful, evidence-based use -ensuring every request adds value to patient care.
Dietitians can play a key role in this stewardship. Rather than re-checking stable results, reviewing test history on EPR systems and liaising with biochemistry colleagues helps reduce duplication. Similarly, understanding the clinical indication for each test ensures our requests are justified. If a patient has low serum levels of a particular micronutrient and the action is to start a broad range multivitamin and mineral supplement, then does another micronutrient need to be tested if the outcome is unlikely to change?
Evidence on the cost of testing
Even apparently low-cost tests add up. In one UK hospital, a single U&E test was costed at approximately £3.65 per assay, with thyroid and vitamin D tests costing £5–£7, and trace element assays considerably more. (3) Costs vary by laboratory and region, but the principle is clear: high-volume testing has a real budgetary impact.
The same study also showed that when clinicians received feedback on the cost of common blood tests, ordering dropped by around 10%, demonstrating that awareness alone can modify behaviour (3).
Digital innovation is helping to refine the way we test. Algorithms that flag duplicate requests or prompt users to justify repeat tests are being rolled out across many NHS trusts, ensuring each request provides meaningful, actionable information.
Clinical value: when do tests add meaning?
Not all assays provide clear clinical value in every context. For example, serum zinc is often requested when deficiency is suspected, but its concentration is tightly regulated and influenced by infection, stress, and diurnal variation. Several reviews note that serum zinc may not change substantially during mild deficiency or short-term supplementation due to homeostatic control. (1, 2) This means a “normal” result does not necessarily exclude functional insufficiency, particularly in the presence of inflammation.
Similarly, selenium levels can vary with acute-phase response, and low plasma values may not always indicate deficiency unless corroborated by dietary or clinical evidence. (4)
By contrast, ferritin remains the most reliable biomarker of iron stores when interpreted with inflammatory markers, and the level will often directly correspond with treatment, be it food first, over-the-counter supplementation, or infusion. (5)
The key takeaway is that biochemical markers vary greatly in their diagnostic sensitivity - knowing when not to test is as important as knowing when to request testing. If deficiency is likely based on risk factors or clinical presentation, evidence-based guidance supports starting supplementation empirically, particularly for nutrients such as vitamin D. Biochemistry remains an essential pillar of dietetic practice, guiding diagnosis, monitoring, and treatment across patient groups. However, with financial and environmental costs under increasing scrutiny, dietitians have a responsibility to consider the necessity and timing of each test.
Simon is a specialist Registered Dietitian working in IMD at University Hospitals Bristol and Weston.
Simon Tapley, Specialist RD in IMD
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References:
Brown, K.H., Rivera, J.A., Bhutta, Z., Gibson, R.S., King, J.C., Lönnerdal, B., Ruel, M.T., Sandtröm, B., Wasantwisut, E. and Hotz, C., 2007. International Zinc Nutrition Consultative Group (IZiNCG) Technical Document 1: Assessment of the risk of zinc deficiency in populations and options for its control. Food and Nutrition Bulletin, 28(3 Suppl 2), pp.S403–S429.
Gibson, R.S. and Hess, S.Y., 2009. Indicators of zinc status at the population level: a review of the evidence. British Journal of Nutrition, 102(S1), pp.S54–S63.
Jones, M., McDonagh, S., Downing, J., et al., 2019. Does cost feedback modify demand for common blood tests in secondary care? BMJ Open
Rayman, M.P., 2012. Selenium and human health. The Lancet, 379(9822), pp.1256–1268.
World Health Organization (WHO), 2011. Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity. Geneva: World Health Organization.
Getting It Right First Time (GIRFT), 2021. Endocrinology National Specialty Report. NHS England, London.
Getting It Right First Time (GIRFT), 2022. Pathology National Specialty Report. NHS England, London.
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