Photo Credit: Selvanegra
Ferritin cutoffs for testing are highly variable in primary care and significantly impact the diagnosis and treatment of iron deficiency in this setting.
Compared with a ferritin cutoff of 15 ng/mL, cutoffs at 30 and 45 ng/mL result in many more people diagnosed with iron deficiency, according to results of a retrospective cohort study published in JAMA Network Open.
“Choosing different ferritin cutoffs within the range of cutoffs recommended by different clinical guidelines can change the incidence rates of iron deficiency diagnoses in primary care by up to a factor of five,” lead author Levy Jäger, MD, PhD, tells Physician’s Weekly (PW).
The researchers analyzed data from 255,351 adults (median age, 52; 52.1% women) who had at least one consultation with any one of 262 clinicians. Only about a quarter of patients (72,817; 28.5%) received ferritin testing.
At ferritin cutoffs of 15, 30, and 45 ng/mL, respectively:
- Iron deficiency diagnoses were 10.9, 29.9, and 48.3 cases per 1,000 patient-years.
- Nonanemic iron deficiency diagnoses were 4.1, 14.6, and 25.8 cases per 1,000 patient-years.
- Anemic iron deficiency diagnoses incidences were 3.5, 6.0, and 7.5 cases per 1,000 patient-years.
Ferritin testing was strongly associated with fatigue (adjusted HR, 2.03; 95% CI, 1.95-2.12), anemia (adjusted HR, 1.75; 95% CI, 1.70-1.79), and iron therapy (adjusted HR, 1.50; 95% CI, 1.46-1.54).
Among patients tested for ferritin, 72.1% received accompanying hemoglobin testing, and 49.6% received accompanying C-reactive protein testing.
Dr. Jäger talked with Physician’s Weekly (PW) to learn more.
PW: Why was it important to conduct this study?
Dr. Jäger: Previous analyses showed that ferritin is one of primary care’s most ordered laboratory tests. However, systematic assessment of iron deficiency rates in primary care, especially of data on non-anemic iron deficiency, was lacking.
Did the study findings surprise you?
Setting a higher ferritin cutoff leads to higher rates of iron deficiency, but we did not expect the magnitude of the effect we observed. In addition, we were appalled by the gaps in the quality of ferritin testing, with hemoglobin and C-reactive protein not requested in a substantial proportion of patients who received ferritin testing. This finding was surprising, as the concomitant assessment of anemia and systemic inflammation is a common recommendation in most clinical guidelines.
The 28.5% rate of patients who received ferritin testing during our 3-year observation period was striking. Although impressive, this figure was not surprising, as a previous analysis of health insurance claims data showed that 27% of the population was tested for serum ferritin in 2018.
How may these results affect patient care?
Our study’s results provide an important information base for assessing ferritin cutoffs at the health system level. This can help inform future policies for managing iron deficiency in primary care.
Our results underscore the need to pay more attention to the choice of ferritin cutoffs, which may influence iron therapy decisions for many patients.
What further research are you planning?
We were very concerned about the quality gaps in ferritin testing we found, and we have just begun to wonder why general practitioners so often omit hemoglobin and C-reactive protein testing when ordering ferritin. We wonder about the role of patient requests and whether clinical laboratories could improve the quality of ferritin testing. For example, we could suggest concomitant hemoglobin and C-reactive testing on ferritin order forms.
In future studies, we may examine how general practitioners interpret their patients’ ferritin concentrations and determine the implicit thresholds they use to prescribe iron therapy.
Is there anything else you’d like to mention?
Our results highlight that the use of an often seemingly innocuous procedure, a simple laboratory test, has a potentially large impact on many patients—and that the choice of an appropriate clinical decision threshold is far from obvious.
