Higher Hemoglobin Levels in Diabetic Subjects With Renal Hyperfiltration

Thomas et al recently reported that the decline in hemoglobin (Hb) level began early in the course of diabetic kidney disease in type 2 diabetic patients.1 Glomerular hyperfiltration is the earliest detectable abnormality in diabetic kidney disease;2 however, Thomas et al did not observe a reduction of Hb during the follow-up of subjects with a baseli ne estimated glomerular filtration rate (GFR) >120 mL/min/1.73 m2 (>2.00 mL/s/1.73 m2). The Modification of Diet in Renal Disease (MDRD) estimation is not accurate at high levels of GFR.3, 4 We measured GFR (51Cr-EDTA) and Hb in 63 diabetic patients. For patients aged >40 years, GFR (mL/min/1.73 m2) was age adjusted by first summing GFR and age (in years), and then subtracting 40 (this correction accounts for the natural decline of GFR with age as proposed by Premaratne et al).5 Hb levels were lower in patients without hyperfiltration. We suggest that the decline in hemoglobin in diabetic kidney disease may begin during the transition from hyperfiltration to normal GFR. Table 1.

Table 1. Characteristics of Diabetic Subjects With and Without Hyperfiltration

		Age-adjusted GFR (mL/min/1.73 m2)		P
		>130	90-130
	n	14	49
	Age-adjusted GFR (mL/min/1.73 m2)	156±20	105±10	<0.001
	Serum creatinine (μmol/L)	79±10	92±18	<0.01
	Albumin excretion rate (mg/24 h)	339±495	207±363	NS
	Age (y)	55±16	61±14	NS
	Diabetes duration (y)	8±6	17±10	<0.005
	Gender	3F, 11M	20F, 29M	NS
	Diabetes type	11 type 2	33 type 2	NS
	BMI (kg/m2)	27.6±4.9	27.3±3.8	NS
	HbA1c (%)	9.8±1.3	9.2±1.6	NS
	Hb (g/dL)	14.3±1.3	13.4±1.4	<0.05
	Red cell volume (fL)	88±4	87±4	NS
	C reactive protein (mg/L)	5.1±2.7	7.6±8.4	NS
	Subjects treated by ACE inhibitors	6	24	NS

Note: Values expressed as mean ± SD. To convert GFR in mL/min to mL/s, multiply by 0.01667; serum creatinine in μmol/L to mg/dL, multiply by 88.4; Hb in g/dL to g/L, multiply by 10. Abbreviations: GFR, glomerular filtration rate; NS, not significant; BMI, body mass index; Hb, hemoglobin; ACE, angiotensin-converting enzyme.