Kidney Function: GFR vs. Creatinine in Chronic Kidney Disease

Glomerular filtration rate and kidney disease issues?

Hello Dr.
Wu,
I am 180 cm tall and weigh around 71 kg.
Recently, for the past month, I have noticed persistent bubbles in my urine, and I feel that I have increased urinary frequency (especially 2-3 hours after consuming sugary drinks) and nocturia.
I am concerned that this may indicate kidney disease or diabetes.
Last week, I visited the hospital and consulted a nephrologist, where I underwent blood and urine tests.
The results showed that the routine urine analysis was normal, with no glucose or protein detected (-).
My uric acid level was 5.6 mg/dL, creatinine was 1.0 mg/dL, and fasting blood glucose was 102 mg/dL (the biological reference range is 70-100).
The doctor indicated that my urine protein levels were normal.
Regarding the slightly elevated fasting blood glucose, he suggested that I see a metabolic specialist for further evaluation.
I confirmed with the doctor whether my kidney function was normal, and he stated that based on the blood and urine test results, everything appeared normal.
He advised me to continue observing the bubbles and to maintain a light diet.

However, after researching online, I learned that creatinine levels alone cannot determine whether kidney function is normal or if there is kidney disease; instead, the glomerular filtration rate (GFR) should be assessed.
I entered my creatinine value into the Kidney Foundation's website (http://kidney.tsn.org.tw/) and obtained a GFR of 88.41.
According to their staging table, this falls under stage 2 chronic kidney disease, which differs from what the doctor told me last week, leaving me confused.
In summary, I would like to ask Dr.
Wu whether my condition indicates normal kidney function or if it suggests impaired kidney function (stage 2 chronic kidney disease).
Thank you for taking the time to clarify this for me.

Liu R, 30~39 year old female. Ask Date: 2016/01/12

Dr. Wu Jiyu reply Internal Medicine

Based on the data you provided, the physician's response is correct because the current formula for estimating glomerular filtration rate (GFR) is derived from international sources, while domestic scholars are researching a formula specific to our population.
In summary, regular monitoring and controlling the three highs (such as your elevated fasting blood glucose levels) may result in a GFR of 90 ml/min/1.73m² or higher at your next check-up.
Thank you for your inquiry.
The Nephrology Department at Changhua Hospital is concerned about your health.

Reply Date: 2016/01/12

More Info

Understanding kidney function is crucial, especially when it comes to interpreting laboratory results related to creatinine and glomerular filtration rate (GFR). In your case, you have raised some important questions regarding your kidney health, particularly in light of your recent symptoms and lab results.

Firstly, let's clarify what creatinine and GFR represent. Creatinine is a waste product generated from muscle metabolism, and its levels in the blood can indicate how well the kidneys are functioning. The normal range for serum creatinine is typically around 0.6 to 1.2 mg/dL, but this can vary based on factors such as age, sex, and muscle mass. In your case, a creatinine level of 1.0 mg/dL falls within the normal range, suggesting that your kidneys are effectively filtering this waste product from your blood.

On the other hand, GFR is a more comprehensive measure of kidney function. It estimates how much blood is passing through the glomeruli (the filtering units of the kidney) each minute. A normal GFR is generally considered to be 90 mL/min/1.73 m² or higher. Your calculated GFR of 88.41 mL/min/1.73 m² is slightly below the normal threshold, which can indicate early signs of kidney dysfunction. According to the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines, a GFR between 60 and 89 mL/min/1.73 m² is classified as Stage 2 chronic kidney disease (CKD), which is a mild reduction in kidney function.

Now, regarding your symptoms of foamy urine and increased frequency of urination, these can be indicative of proteinuria (the presence of excess protein in the urine), which is often a sign of kidney damage. However, your urine tests showed no protein or glucose, which is reassuring. The foamy appearance of urine can sometimes be due to the speed of urination or the concentration of urine rather than an indication of kidney disease. It’s important to monitor this symptom, especially if it persists.

Your slightly elevated fasting blood glucose level (102 mg/dL) is also noteworthy. While it is only marginally above the normal range, it suggests that you may be at risk for developing insulin resistance or prediabetes. This condition can have implications for kidney health, as diabetes is a leading cause of chronic kidney disease. Therefore, it would be prudent to follow up with a metabolic specialist as your doctor suggested.

In summary, while your creatinine level is normal, your GFR indicates a mild reduction in kidney function, which could be classified as Stage 2 CKD. This does not necessarily mean that you have significant kidney disease, but it does warrant monitoring and lifestyle adjustments. It is essential to maintain a healthy diet, manage your blood sugar levels, and stay hydrated. Regular follow-ups with your healthcare provider for kidney function tests and monitoring of your blood glucose levels will be important in managing your overall health.

If you continue to experience symptoms or if your lab results change, further investigations may be necessary to rule out any underlying conditions. Always consult with your healthcare provider for personalized advice and treatment options based on your specific health needs.

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