Table 1.

Guideline definition of ID in general population and chronic disease; summary of current ID laboratory measurements

Professional association	Origin	Year	Condition	Threshold values for ID diagnostic
				Serum ferritin (μg/L)	TSAT (%)	Additional biomarkers
General population
WHO [38]	International	2020	ID in		–	sTfR#, CRP**
			˗ Infants and children < 5 years	< 12
			with infection/inflammation	< 30
			˗ Children > 5 years, adolescents, adults, older person (60 + years)	< 15
			with infection/inflammation	< 70
			˗ Pregnant women (only for first trimester)	< 15
AAFP [39]	American	2013	IDA	< 30	–	low serum iron#, low TSAT#, high TIBC#
			with infection/ inflammation	< 50
BCG [40]	British	2019	ID in children	< 12	additional < 20	serum iron#, TIBC#, TSAT
			- Possible ID	12–20
			ID in adults	< 15
			- Probable ID	15–30
			- Unlikely ID	> 30
			or with chronic inflammatory disease	> 70–100
			or in elderly patients	> 50
Chronic heart failure (HF)
ACCF/AHA [30]	American	2017	AID	< 100	–	–
			FID	or 100–300	and < 20
ESC [23]	European	2021	AID	< 100	and < 20	sTfR#
			FID	or 100–299	and < 20
Chronic kidney disease (CKD)
KIDIGO [31]	International	2012	IDA only	–	–	–
			ND/HD-CKD + IDA	≤ 500	and ≤ 30
			Pediatric CKD + IDA	≤ 100	and ≤ 20
			Severe ID	≤ 30	–
KDOQI [32]	American	2013	IDA only	–	–	–
ERBP [33]	European	2013	ID/IDA (AID)	< 100	and < 20	–
UK NICE [34]	British	2021	IDA only	< 100*	and < 20*	Red blood cell markers: %HRC > 6%, CHr < 29 pg
JSDT [35] (2015 version)	Japanese	2017	HD-CKD + ID	≤ 100	≤ 20	–
Inflammatory bowel disease (IBD)
ECCO [21]	European	2015	ID/IDA (quiescent disease, without inflammation)	< 30	–	Tests to distinguish between IDA and ACD: sTfR, sTfR–ferritin index
			AID and ACD	30–100	and/or < 20
			FID and ACD	> 100	and < 20
BSG [36]	British	2021	ID/IDA (AID)	< 15	–	sTfR# (in healthy subjects), sTfR–ferritin index#, CHr#, HYPO%# (in chronic disease and/or raised ESR#, CRP)
			FID	≥ 100	< 20
Cancer
NCCN [37]	America	2021	ID/IDA (AID)	< 30	and < 20	–
			FID (often when receiving ESAs)	30–500	and < 50
			Possible FID	> 500–800	and < 50
ESMO [20]	European	2018	ID/IDA (AID)	< 30–100	and < 20	AID: sTfR#, ZPP# AID and FID: %HYPO > 5%, CHr < 28 pg, CRP**
			FID	> 100	and < 20
DGHO [11]	Germany	2022	ID/IDA (AID)	< 30–100	< 20	sTfR > 0.76–1.76 mg/L (Dade Behring Test), sTfR–ferritin index > 0.2–3.7 men, > 0.6–3.8 women (Roche Test), ZPP > 80 µmol/mol Häm, HYPO% > 10%, CHr < 26 pg, CRP**
			FID	100–800	and < 20

%HRC percentage of hypochromic red cells, AAFP American Academy of Family Physicians, ACCF American College of Cardiology Foundation, ACD Anemia of chronic disease, AHA American Heart Association, AID absolute iron deficiency, BCG British Columbia Guidance, BSG British Society of Gastroenterology, CHr reticulocyte hemoglobin content, CRP C-reactive protein, DGHO Deutsche Gesellschaft für Hämatologie und Onkologie, ECCO European Crohn’s and Colitis Organisation, ERBP European Renal Best Practice, ESA Erythropoiesis-Stimulating Agents, ESC European Society of Cardiology, ESMO European Society for Medical Oncology, ESR erythrocyte sedimentation rate, FID functional iron deficiency, HYPO% hypochromic erythrocytes, ID iron deficiency, IDA iron deficiency anemia, JSDT Japanese Society for Dialysis Therapy, KDIGO Kidney Disease Improving Global Outcomes, KDOQI Kidney Disease Outcomes Quality Initiative, NCCN National Comprehensive Cancer Network, NICE National Clinical Guideline Centre, sTfR soluble transferrin receptor, TSAT transferrin saturation, WHO World Health Organization, ZPP zinc protoporphyrin

^* Second line, not recommended as stand-alone measurement

^** Inflammatory condition [CRP < 5 mg/L]

^# no cut-off values indicated