A novel method for creatinine adjustment makes the revised Lund–Malmö GFR estimating equation applicable in children

Figures & data

Table 1. Patient characteristics.

	All (n = 4005)	mGFR < 75 mL/min/1.73 m^2(n = 932)	mGFR ≥ 75 mL/min/1.73 m^2(n = 3073)
Age (years)	12.0 (2.5–17.7)	12.8 (2.9–17.7)	12.0 (2.5–17.8)
Females, n (%)	1694 (42)	385 (41)	1309 (43)
Weight (kg)	40 (13–83)	41 (13–80)	40 (13–84)
Height (cm)	148 (90–183)	149 (89–181)	148 (90–184)
Body surface area (m^2)	1.30 (0.56–2.01)	1.31 (0.54–1.96)	1.29 (0.56–2.03)
Body mass index (kg/m^2)	18 (14–29)	18 (13–30)	18 (14–29)
Plasma/serum creatinine (μmol/L)	54 (21–139)	83 (37–275)	48 (20–91)
Measured GFR (mL/min/1.73 m^2)	96 (30–167)	58 (17–74)	104 (77–172)
Measured GFR, number (%)
<30 mL/min/1.73 m^2	95 (2.4)	95 (10)
30–44 mL/min/1.73 m^2	134 (3.3)	134 (14)
45–59 mL/min/1.73 m^2	264 (6.6)	264 (28)
60–74 mL/min/1.73 m^2	439 (11)	439 (47)
75–89 mL/min/1.73 m^2	679 (17		679 (22)
90–119 mL/min/1.73 m^2	1606 (40)		1606 (52)
≥120 mL/min/1.73 m^2	788 (20)		788 (26)

Descriptive measures given as median values (2.5 and 97.5 percentiles) if not stated otherwise.

Figure 1. Plasma/serum creatinine values in 83,157 patients from the reference cohort as a function of age in (A) females (n = 57 > 180 μmol/L) and (B) males (n = 130 > 180 μmol/L). The double line represents the creatinine growth curve based on linear regression with fractional polynomials of age as independent variable (see text).

Figure 2. Individual creatinine growth projections for two hypothetical example pairs of children: (1) age 6 years and normal creatinine levels (boy 34 and girl 35 µmol/L), (2) age 12 years with elevated creatinine levels (boy 121 and girl 108 µmol/L) indicating chronic kidney disease (CKD). Adjusted creatinine for the Lund–Malmö revised equation (LMR18) is obtained by following the corresponding growth curve until age 18 years (marked with crosses).

Table 2. Bias, precision, accuracy (95% confidence intervals) of GFR estimating equations in children 2.0–17.9 years stratified for measured GFR <75 (n = 932) and ≥75 mL/min/1.73 m² (n = 3 073).

Equations	Bias (mL/min/1.73 m^2)	Precision (mL/min/1.73 m^2)	Absolute percentage error	P10 (%)	P30 (%)
mGFR <75 (median 58) mL/min/1.73 m^2
CKiD	7.4 (6.2–8.3)	18.0	16.2 (15.1–17.8)	32.7 (29.7–35.7)	71.8 (68.9–74.7)
Schwartz–Lyon	2.3 (1.5–3.1)	14.7	13.0 (12.1–14.0)	39.8 (36.7–42.9)	80.8 (78.3–83.3)
LMR	14.4 (13.2–15.8)	18.9	26.5 (24.4–28.1)	20.6 (18.0–23.2)	55.6 (52.4–58.8)
LMR18	4.8 (3.7–5.9)	18.0	16.0 (15.0–17.7)	32.7 (29.7–35.7)	74.4 (71.6–77.2)
mGFR ≥75 (median 104) mL/min/1.73 m^2
CKiD	3.4 (2.4–4.4)	30.3	14.5 (13.9–15.0)	36.1 (34.4–37.8)	82.1 (80.7–83.5)
Schwartz–Lyon	−5.6 (−6.4 to −4.6)	26.2	13.8 (13.3–14.3)	37.7 (36.0–39.5)	86.7 (85.5–87.9)
LMR	−4.9 (−5.6 to −4.2)	25.4	12.4 (11.7–12.9)	41.7 (40.0–43.5)	88.9 (87.8–90.0)
LMR18	−8.2 (−9.2 to −7.4)	23.2	12.5 (11.9–12.9)	41.1 (39.3–42.8)	90.2 (89.1–91.2)

Median bias (eGFR-mGFR) and precision (interquartile range) expressed in mL/min/1.73 m², and accuracy expressed as median absolute percentage error |(eGFR − mGFR)/mGFR|, and P₁₀ and P₃₀ accuracy (percentage of GFR estimates within ±10% and ±30% of mGFR).

CKiD: Chronic Kidney Disease in Children; LMR: Lund–Malmö revised; LMR18: LMR based on creatinine values adjusted to the age of 18 years; eGFR: estimated glomerular filtration rate; mGFR: measured GFR.

Figure 3. Associations in the validation cohort between age groups and median bias (estimated GFR – measured GFR) of the Lund–Malmö revised equation, both in the original formulation (LMR) and with creatinine adjusted to age 18 years (LMR18). Results stratified by (A) females with mGFR <75 (n = 385) and ≥75 mL/min/1.73 m² (n = 1309) and (B) males with measured GFR (mGFR) <75 (n = 547) and ≥75 mL/min/1.73 m² (n = 1764).

Table 3. Bias and accuracy (P₃₀) of GFR estimating equations in children 2.0–17.9 years old stratified by sex and measured GFR <75 and ≥75 mL/min/1.73 m².

	N (%)	Median mGFR	CKiD	Schwartz–Lyon	LMR	LMR (18)
mGFR <75 mL/min/1.73 m^2
Bias
Girls	385 (41)	59	9.8	2.9	10.8	4.7
Boys	547 (59)	58	4.7	1.7	17.2	4.8
P30 (%)
Girls			67	82	66	76
Boys			75	80	48	73
mGFR ≥75 mL/min/1.73 m^2
Bias
Girls	1309 (43)	103	7.5	−4.7	−6.8	−8.2
Boys	1764 (57)	104	0.7	−6.2	−3.1	−8.2
P30 (%)
Girls			82	88	89	90
Boys			82	86	89	90

Median bias (eGFR – mGFR) expressed in mL/min/1.73 m² and P₃₀ accuracy as percentage of GFR estimates within ±30% of mGFR.

CKiD: Chronic Kidney Disease in Children; LMR: Lund–Malmö revised; LMR18: LMR based on creatinine values adjusted to age 18 years; eGFR: estimated glomerular filtration rate; mGFR: measured GFR.

Data availability statement

The EKFC dataset used in the present study is hosted by the Lund University Population Research Platform (LUPOP). Legal and ethical restrictions prevent public sharing of the dataset. Data can be made available for collaborations upon request to interested researchers but would generally require a new ethical permission and the permission of each of the data-owners. You can find contact information for the data host at https://www.lupop.lu.se/