Insufficient classification of anaemia in general practice: a Danish register-based observational study

Figures & data

Table 1. Demographic and clinical characteristics of individuals aged 40–90 years with new-onset anaemia detected in general practice (n = 62,731).

Patient characteristics	Men, n (%)	Women, n (%)	Total, n (%)
Total^a	35,075 (55.9)	27,656 (44.1)	62,731 (100.0)
Age groups, years
40–49	2,567 (7.3)	7,256 (26.2)	9,823 (15.7)
50–59	4,990 (14.2)	3,882 (14.0)	8,872 (14.1)
60–69	8,848 (25.2)	3,714 (13.4)	12,562 (20.0)
70–79	11,265 (32.1)	6,012 (21.7)	17,277 (27.5)
80–89	7,405 (21.1)	6,792 (24.6)	14,197 (22.6)
Educational level
Low	13,618 (38.8)	13,312 (48.1)	26,930 (42.9)
Medium	15,193 (43.3)	8,798 (31.8)	23,991 (38.2)
High	6,264 (17.9)	5,546 (20.1)	11,810 (18.8)
Income
Low	11,853 (33.8)	9,045 (32.7)	20,898 (33.3)
Medium	10,709 (30.5)	10,159 (36.7)	20,868 (33.3)
High	12,513 (35.7)	8,452 (30.6)	20,965 (33.4)
Civil status
Living with a partner	21,834 (62.2)	13,464 (48.7)	35,298 (56.3)
Living alone	13,241 (37.8)	14,192 (51.3)	27,433 (43.7)
Anaemia severity^b
Mild	32,736 (93.3)	16,693 (60.4)	49,429 (78.8)
Moderate	1,999 (5.7)	10,047 (36.3)	12,046 (19.2)
Severe	340 (1.0)	916 (3.3)	1,256 (2.0)
Number of comorbidities
0	16,457 (46.9)	14,654 (53.0)	31,111 (49.6)
1	9,180 (26.2)	6,421 (23.2)	15,601 (24.9)
2	5,876 (16.8)	3,943 (14.3)	9,819 (15.7)
≥3	3,562 (10.2)	2,638 (9.5)	6,200 (9.9)
Type of comorbidity^c
Cardiovascular disease	10,577 (30.2)	5,672 (20.5)	16,249 (25.9)
Hypertension	7,890 (22.5)	6,179 (22.3)	14,069 (22.4)
Mental illness	2,395 (6.8)	3,012 (10.9)	5,407 (8.6)
Diabetes	3,835 (10.9)	2,591 (9.4)	6,426 (10.2)
Chronic obstructive pulmonary disease	2,158 (6.2)	1,657 (6.0)	3,815 (6.1)
Neurological disorder	1,141 (3.3)	743 (2.7)	1,884 (3.0)
Arthritis	226 (0.6)	401 (1.4)	627 (1.0)
Inflammatory bowel disease	317 (0.9)	302 (1.1)	619 (1.0)
Liver disease	480 (1.4)	333 (1.2)	813 (1.3)
Kidney disease	622 (1.8)	422 (1.5)	1,044 (1.7)
Cancer	3,041 (8.7)	1,801 (6.5)	4,842 (7.7)

^aTotal numbers are shown in row percentages; all other variables are shown in column percentages.

^bAnaemia severity was defined according to WHO’s guidelines: mild anaemia (110 g/L-normal value), moderate anaemia (80–110 g/L), and severe anaemia (<80 g/L).

^cA person was categorised as having comorbidity within the specified chronic disease group (e.g. cardiovascular disease).

If the person had any of the included diseases (e.g. ischaemic heart disease) listed under the chronic disease group (Supplementary File 1).

Figure 1. Percentage^a of patients with anaemia classified into subtypes of anaemia (n = 62,731). AI: anaemia of inflammation; CIIDA: combined inflammatory iron deficiency anaemia; IDA: iron deficiency anaemia; MCV: mean cell volume. ^aAdjusted percentages were calculated by setting age at 70–79 years. Error bars = 95% confidence intervals.

Figure 2. Percentage^a of patients with anaemia who received subsequent laboratory tests in the following 3 months (n = 62,731). CRP: C-reactive protein; RDW: red cell distribution width. ^aAdjusted percentages were calculated by setting age at 70–79 years. Error bars = 95% confidence intervals.

Table 2. The likelihood and percentage of patients having unclassified anaemia according to the aetiological algorithm and the association with patient characteristics (n = 62,731).

Patient characteristics	Men		Women
	OR (CI)^a	Percentage (CI)^b	OR (CI)^a	Percentage (CI)^b
Age groups, years
40–49	1	69.3% (66.9–71.7)	1	43.2% (41.1–45.4)
50–59	1.25 (1.13–1.40)	73.9% (71.8–76.0)	1.48 (1.36–1.61)	53.0% (50.9–55.2)
60–69	1.45 (1.31–1.61)	76.6% (74.9–78.4)	1.96 (1.78–2.15)	59.8% (57.7–62.0)
70–79	1.68 (1.52–1.86)	79.1% (77.5–80.8)	2.40 (2.20–2.62)	64.7% (62.7–66.6)
80–89	1.86 (1.68–2.07)	80.8% (79.1–82.4)	3.00 (2.73–3.29)	69.5% (67.6–71.5)
Educational level
Low	1	79.4% (77.7–81.2)	1	65.3% (63.4–67.2)
Medium	1.01 (0.95–1.08)	79.6% (78.0–81.3)	0.89 (0.84–0.95)	62.7% (60.7–64.6)
High	0.99 (0.91–1.09)	79.3% (77.4–81.2)	0.81 (0.76–0.87)	60.5% (58.3–62.6)
Income
Low	1	78.7% (77.0–80.4)	1	64.2% (62.2–66.2)
Medium	1.07 (1.01–1.15)	79.9% (78.3–81.5)	1.05 (0.99–1.12)	65.4% (63.5–67.2)
High	1.08 (1.01–1.16)	79.9% (78.2–81.6)	0.84 (0.78–0.90)	60.2% (58.1–62.3)
Civil status
Living alone	1	79.7% (78.1–81.4)	1	64.8% (62.9–66.6)
Living with a partner	0.99 (0.94–1.05)	79.6% (77.9–81.2)	0.91 (0.87–0.96)	62.7% (60.8–64.6)
Anaemia severity^b
Mild	1	81.4% (79.8–82.9)	1	71.8% (70.0–73.5)
Moderate	0.25 (0.23–0.28)	52.5% (49.8–55.2)	0.40 (0.38–0.43)	50.6% (48.6–52.7)
Severe	0.21 (0.17–0.27)	48.1% (42.2–53.9)	0.24 (0.20–0.28)	37.6% (33.8–44.4)
No. of comorbidities
0	1	78.2% (76.5–80.0)	1	59.2% (57.2–61.1)
1	1.08 (1.02–1.15)	79.6% (77.8–81.3)	1.38 (1.30–1.47)	66.7% (64.7–68.7)
2	1.14 (1.05–1.23)	80.4% (78.6–82.2)	1.44 (1.33–1.55)	67.6% (65.4–69.7)
≥3	1.25 (1.14–1.37)	81.8% (80.0–83.6)	1.44 (1.31–1.58)	67.6% (65.3–69.9)
Type of comorbidity^c
Cardiovascular disease	1.08 (1.02–1.14)	80.4% (78.7–82.0)	1.13 (1.06–1.21)	65.8% (63.8–67.9)
Hypertension	1.12 (1.05–1.19)	80.9% (79.3–82.5)	1.23 (1.15–1.31)	67.0% (65.0–69.1)
Mental illness	1.08 (0.98–1.20)	80.8% (78.7–82.9)	1.28 (1.18–1.39)	68.8% (66.6–71.0)
Diabetes	1.34 (1.21–1.47)	83.5% (81.8–85.1)	1.27 (1.16–1.39)	68.4% (66.1–70.7)
COPD	0.92 (0.82–1.03)	78.4% (76.0–80.7)	1.09 (0.98–1.21)	65.5% (62.8–68.2)
Neurological disorder	1.12 (0.96–1.29)	81.3% (78.8–83.8)	1.30 (1.11–1.52)	69.3% (65.8–72.9)
Arthritis	1.02 (0.75–1.40)	80.0% (74.6–85.4)	1.38 (1.10–1.74)	70.7% (65.6–75.8)
IBD	1.02 (0.79–1.31)	79.9% (75.6–84.2)	1.22 (0.97–1.52)	68.1% (62.9–73.2)
Liver disease	0.92 (0.75–1.13)	78.3% (74.4–82.2)	1.13 (0.90–1.42)	66.4% (61.2–71.7)
Kidney disease	1.22 (0.99–1.50)	82.6% (79.4–85.8)	1.50 (1.21–1.86)	72.3% (67.7–76.9)
Cancer	1.04 (0.95–1.15)	80.2% (78.2–82.2)	1.39 (1.25–1.54)	70.3% (67.7–72.9)

CI: 95% confidence intervals; COPD: chronic obstructive pulmonary disease; IBD: inflammatory bowel disease; OR: odds ratio.

^aOdds ratios (of having unclassified anaemia vs. classified anaemia according to patient characteristics) were adjusted for age.

^bAdjusted percentages were calculated by setting the age at 70–79 years.

^cAnaemia severity was defined according to WHO’s guidelines: mild anaemia (110 g/L-normal value), moderate anaemia (80–110 g/L), and severe anaemia (<80 g/L).

^dA person was categorised as having comorbidity within the specified chronic disease group (e.g. cardiovascular disease) if the person had any of the included diseases (e.g. ischaemic heart disease) listed under the chronic disease group (Supplementary File 1).

^eThe reference group for each of the comorbidities is patients without the specified comorbidity (e.g. the reference group for cardiovascular disease in patients without cardiovascular disease).