Serum Creatinine to Cystatin C Ratio is an Effective Indicator for Muscle Strength Decline in Men with Acute Exacerbation of Chronic Obstructive Pulmonary Disease

Figures & data

Table 1 Comparison of Characteristics Between Stable COPD and AECOPD Groups

Clinical Characteristics	Stable COPD Group (n = 32)	AECOPD Group (n = 72)		P value
Age (years)	65.13±9.67	68.25±7.70		0.081
Height (m)	1.65(1.62–1.69)	1.64(1.61–1.67)		0.260
Weight(kg)	55.27±7.78	53.70±9.05		0.398
BMI (kg/m^2)	20.50±2.98	20.08±3.38		0.544
Underweight^a (n, %)	8(25.00%)	25(34.72%)		0.355
Normal weight^b (n, %)	20(62.50%)	37(51.40%)		0.277
Overweight^c (n, %)	4(12.50%)	10(13.90%)		0.612
Smoking history (Yes/No)	30/2	64/8		0.720
Course of disease (months)	48(36.00–114.00)	84(51–120)		0.055
Acute exacerbations ≥2 within one year (Yes/No)	9/23	26/46		0.504
HGS (kg)	34.00(27.80–35.40)	29.20(22.70–31.70)		<0.01
mMRC score	1.5(0.00–3.0)	2(2–3)		<0.01
CAT score	9.0(4.0–17)	19(14–22)		<0.01
FEV1 (L)	1.23(0.78–1.53)	0.86(0.63–1.20)		<0.01
FVC (L)	2.50±0.74	2.03±0.62		<0.01
FEV1/FVC	48.71±9.33	45.34±9.10		0.088
FEV1%pred	45.93±16.88	36.51±15.29		<0.01
Cr (mg/dl)	0.94±0.19	0.81±0.14		<0.01
CysC (mg/L)	0.89±0.18	0.86±0.15		0.478
Cr/CysC ratio	1.08(0.91–1.23)	0.91(0.84–1.10)		<0.01
Urea nitrogen (μmol/L)	5.10(4.06–6.18)	5.14(4.36–6.20)		0.610

Notes: ^aUnderweight (BMI<18.5 kg/m²); ^bNormal weight (18.5 kg/m² ≤BMI< 24 kg/m²); ^cOverweight (24 kg/m² ≤BMI< 28 kg/m²).

Abbreviations: COPD, chronic obstructive pulmonary disease; AECOPD, acute exacerbation of chronic obstructive pulmonary disease; BMI, body mass index; HGS, handgrip strength; mMRC, modified British Medical Research Council; CAT, COPD Assessment Test; FEV₁, forced expiratory volume in 1 second; FVC, functional vital capacity; FEV₁/FVC, forced expiratory volume in 1 second /forced vital capacity; FEV₁%pred, percent of forced expiratory volume in 1 second; Cr, creatinine; CysC, cystatin C; Cr/CysC, creatinine/cystatin C.

Table 2 Comparison of Clinical Characteristics Between Normal Muscle Strength and Low Muscle Strength Groups of AECOPD Patients

Clinical Characteristics	Normal Muscle Strength Group (n = 41)	Low Muscle Strength Group (n = 31)	P value
Age (years)	66.22(59.27–72.22)	69.04(64.51–75.96)	0.055
Height (m)	1.63±0.05	1.65±0.06	0.113
Weight (kg)	56.33±8.32	50.23±8.92	0.004
BMI (kg/m^2)	21.28±3.15	18.48±3.03	<0.01
Underweight^a (n, %)	8(19.50%)	17(54.80%)	0.351
Normal weight^b (n, %)	24(58.50%)	13(41.90%)	0.703
Overweight^c (n, %)	9(22.00%)	1(3.20%)	0.862
Smoking history (Yes/No)	2/39	6/25	0.068
Course of disease (months)	73(48–120)	120(60–120)	0.228
Acute exacerbations ≥2 times within one year (Yes/No)	10/31	16/15	0.026
HGS (kg)	31.50(30.30–37.00)	22.30(20.40–24.70)	<0.01
mMRC score	2(1–3)	3(2–3)	0.067
CAT score	17.15±6.90	19.52±5.85	0.145
FEV1 (L)	0.90(0.71–1.38)	0.77(0.52–1.06)	0.027
FVC (L)	2.19±0.67	1.81±0.47	<0.01
FEV1/FVC	46.41±8.39	43.94±9.93	0.257
FEV1%pred	39.93±16.46	32.00±12.44	0.028
Cr/CysC ratio	1.02(0.87–1.16)	0.85(0.80–0.92)	<0.01
Cr (mg/dl)	0.83±0.11	0.78±0.17	0.191
CysC (mg/L)	0.83±0.13	0.90±0.17	0.086
Urea nitrogen (μmol/L)	5.03(4.25–5.92)	5.45(4.50–6.33)	0.363

Notes: ^aUnderweight (BMI<18.5 kg/m²); ^bNormal weight (18.5 kg/m² ≤BMI< 24 kg/m²); ^cOverweight (24 kg/m² ≤BMI< 28 kg/m²).

Abbreviations: BMI, body mass index; HGS, handgrip strength; mMRC, modified British Medical Research Council; CAT, COPD Assessment Test; FEV₁, forced expiratory volume in 1 second; FVC, functional vital capacity; FEV₁/FVC, forced expiratory volume in 1 second/forced vital capacity; FEV₁% pred, percent of forced expiratory volume in 1 second; Cr/CysC, creatinine/cystatin C; Cr, creatinine; CysC, cystatin C.

Table 3 Relationships of Serum Cr, Cr/CysC Ratio, and CysC with Clinical Characteristics in Patients with AECOPD

	Cr/CysC Ratio		Cr		CysC
	r value	P value	r value	P value	r value	P value
Weight (kg)	0.469	<0.01	0.241	0.042	−0.242	0.041
BMI (kg/m^2)	0.469	<0.01	0.307	<0.01	−0.188	0.113
HGS (kg)	0.388	<0.01	0.187	0.115	−0.172	0.148
FEV1 (L)	0.246	0.037	0.201	0.091	−0.098	0.414
FVC (L)	0.332	<0.01	0.215	0.070	−0.147	0.217
FEV1%pred	0.244	0.039	0.287	0.014	−0.039	0.742

Abbreviations: Cr/CysC, creatinine/cystatin C; Cr, creatinine; CysC, cystatin C; BMI, body mass index; HGS, handgrip strength; FEV₁, forced expiratory volume in 1 second; FVC, functional vital capacity; FEV₁% pred, percent of forced expiratory volume in 1 second.

Figure 1 ROC curve analysis of Cr/CysC ratio and Cr for low muscle strength.

Abbreviations: Cr, creatinine; Cr/CysC, creatinine/cystatin C.

Table 4 Analysis of Risk Factors for Low Muscle Strength in Male Patients with AECOPD

Factor	Regression Coefficient	Standard Error	Wald	P	OR	95% CI
Cr/CysC ratio	1.754	0.663	7.680	<0.05	5.779	1.671–19.982
Weight(kg)	−0.037	0.036	1.059	>0.05	0.964	0.898–1.034
FVC (L)	−0.630	1.134	0.309	>0.05	0.532	0.058–4.920
FEV1 (L)	0.160	1.670	0.009	>0.05	1.173	0.044–30.970

Abbreviations: Cr/CysC, creatinine/cystatin C; FVC, functional vital capacity; FEV₁, forced expiratory volume in 1 second.