New definition for iron deficiency in CV disease proposed

Evaluating definitions of iron deficiency

The prospective study, called PVDOMICS, entered 1,195 subjects with available iron levels. After exclusion of 38 patients with sarcoidosis, myeloproliferative disease, or hemoglobinopathy, there remained 693 patients with “overt” PH, 225 with a milder form of PH who served as PVD comparators, and 90 age-, sex-, race/ethnicity- matched “healthy” adults who served as controls.

According to the conventional HF definition of iron deficiency – that is, ferritin 100-299 ng/mL and TSAT less than 20% – the prevalences were 74% in patients with overt PH and 72% of those “across the PVD spectrum.”

But by that definition, iron deficient and non-iron deficient patients didn’t differ significantly in peakVO2, 6MWT distance, or SF-36 physical component scores.

In contrast, patients meeting the alternative definition of iron deficiency of TSAT less than 21% showed significantly reduced functional and QoL measures, compared with those with TSAT greater than or equal to 21%.

The group with TSAT less than 21% also showed significantly more RV remodeling at cardiac MRI, compared with those who had TSAT greater than or equal to 21%, but their invasively measured pulmonary vascular resistance was comparable.

Of note, those with TSAT less than 21% also showed significantly increased all-cause mortality (hazard ratio, 1.63; 95% confidence interval, 1.13-2.34; P = .009) after adjustment for age, sex, hemoglobin, and natriuretic peptide levels.

“Proper validation of the definition of iron deficiency is important for prognostication,” the published report states, “but also for providing a working definition that can be used to identify suitable patients for inclusion in randomized controlled trials” of drugs for iron deficiency.

Additionally, the finding that TSAT less than 21% points to patients with diminished functional and exercise capacity is “consistent with more recent studies in the field of heart failure” that suggest “functional abnormalities and adverse cardiac remodeling are worse in patients with a low TSAT.” Indeed, the report states, such treatment effects have been “the most convincing” in HF trials.
 

Broader implications

An accompanying editorial agrees that the study’s implications apply well beyond PH. It highlights that iron deficiency is common in PH, while such PH is “not substantially different from the problem in patients with heart failure, chronic kidney disease, and cardiovascular disease in general,” lead editorialist John G.F. Cleland, MD, PhD, University of Glasgow, said in an interview. “It’s also common as people get older, even in those without these diseases.”

Dr. Cleland said the anemia definition currently used in cardiovascular research and practice is based on a hemoglobin concentration below the 5th percentile of age and sex in primarily young, healthy people, and not on its association with clinical outcomes.

“We recently analyzed data on a large population in the United Kingdom with a broad range of cardiovascular diseases and found that unless anemia is severe, [other] markers of iron deficiency are usually not measured,” he said. A low hemoglobin and TSAT, but not low ferritin levels, are associated with worse prognosis.

Dr. Cleland agreed that the HF-oriented definition is “poor,” with profound implications for the conduct of clinical trials. “If the definition of iron deficiency lacks specificity, then clinical trials will include many patients without iron deficiency who are unlikely to benefit from and might be harmed by IV iron.” Inclusion of such patients may also “dilute” any benefit that might emerge and render the outcome inaccurate.

But if the definition of iron deficiency lacks sensitivity, “then in clinical practice, many patients with iron deficiency may be denied a simple and effective treatment.”

Measuring serum iron could potentially be useful, but it’s usually not done in randomized trials “especially since taking an iron tablet can give a temporary ‘blip’ in serum iron,” Dr. Cleland said. “So TSAT is a reasonable compromise.” He said he “looks forward” to any further data on serum iron as a way of assessing iron deficiency and anemia.