Investigations

Take the following tests before giving a blood transfusion: ^a

^{Microcytic anaemia}

• ferritin ^a  

Why?

A low ferritin makes iron-deficiency anaemia more likely, but a normal level cannot exclude it

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability
anaemia a (pre-test probability: 36%)	iron-deficiency anaemia (bone marrow aspiration)	serum ferritin < 15 µg/l	52 (42 to 62)	97%
		15 - 25 µg/l	8.8 (7.2 to 10)	83%
		25 - 35 µg/l	2.5 (2.1 to 3.0)	58%
		35 - 45 µg/l	1.8 (1.5 to 2.2)	50%
		45 - 100 µg/l	0.54 (0.48 to 0.60)	23%
		≥ 100 mg/l	0.08 (0.07 to 0.09)	4%

Ferritin remains useful in patients with liver cirrhosis

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
liver cirrhosis and anaemia a (pre-test probability: 19%)	iron-deficiency anaemia (bone marrow aspiration)	serum ferritin < 200	4.3 (2.3 to 8.2)	74%	0.22 (0.10 to 0.49)	13%

• Other investigations such as red cell protoporphyrin and transferrin saturation are less helpful at diagnosing iron-deficiency anaemia . ^a