A 65-year-old man with type 2 diabetes mellitus comes to the physician for a routine follow-up appointment. He was started on oral hypoglycemic medications 12 years ago but was recently switched to long-acting insulin due to inadequate blood sugar control. His last serum creatinine level was 2.1 mg/dL. The patient is concerned about his elevated creatinine level and how it relates to his kidney function. Which of the following graphs most accurately represents the relationship between serum creatinine and glomerular filtration rate?

Question

A 65-year-old man with type 2 diabetes mellitus comes to the physician for a routine follow-up appointment.  He was started on oral hypoglycemic medications 12 years ago but was recently switched to long-acting insulin due to inadequate blood sugar control.  His last serum creatinine level was 2.1 mg/dL.  The patient is concerned about his elevated creatinine level and how it relates to his kidney function.  Which of the following graphs most accurately represents the relationship between serum creatinine and glomerular filtration rate?

Quizplus · Accepted Answer

11ec160b_3cec_40ac_9249_fb265a963868_MD0001_00 Serum creatinine is the most common indicator of kidney function in clinical use. Steady-state creatinine levels are a result of the balance between creatinine synthesis in the muscle and excretion via glomerular filtration and proximal tubule secretion. For the most part, creatinine synthesis and tubular secretion remain relatively constant. As a result, serum creatinine levels depend primarily on the glomerular filtration rate (GFR). The relationship between serum creatinine and GFR is nonlinear. A person's serum creatinine can be essentially normal even after a 50% loss of kidney function (ie, following kidney donation or unilateral nephrectomy). Serum creatinine levels begin to rise significantly as the GFR declines to <60 mL/min (assuming no change in muscle mass). As the GFR continues to decline, the slope of the creatinine-GFR curve steepens. Consequently, when the GFR is significantly decreased, small decrements in GFR produce relatively large changes in serum creatinine. However, when the GFR is normal, relatively large decreases in GFR result in only small increases in serum creatinine. Serum creatinine is therefore an insensitive indicator for decreasing GFR when creatinine levels are normal. Educational objective: When the glomerular filtration rate (GFR) is normal, relatively large decreases in GFR result in only small increases in serum creatinine. Conversely, when the GFR is significantly decreased, small decrements in GFR produce relatively large changes in serum creatinine. A good rule of thumb is that every time GFR halves, serum creatinine doubles.

A 65-Year-Old Man with Type 2 Diabetes Mellitus Comes to the Physician