From the Guidelines
Low serum creatinine levels can occur due to several factors, including decreased muscle mass, malnutrition, liver disease, pregnancy, or certain medications, and the most recent evidence suggests that these factors can lead to reduced creatinine production or altered kidney function 1.
Causes of Low Serum Creatinine Levels
The causes of low serum creatinine levels can be categorized into several factors, including:
- Decreased muscle mass, which can be due to malnutrition, muscle-wasting conditions, or old age and female sex 1
- Liver disease, which can decrease creatinine levels because the liver produces creatine, which muscles convert to creatinine 1
- Pregnancy, which can increase blood volume and dilute creatinine concentration 1
- Certain medications, such as trimethoprim and cimetidine, which can interfere with creatinine secretion or measurement 1
Clinical Implications
Low serum creatinine levels are not typically treated directly, but rather by addressing the underlying cause. If a patient has unexpectedly low creatinine, their healthcare provider may investigate for muscle disorders, nutritional deficiencies, or liver dysfunction, especially if accompanied by other symptoms 1.
Diagnostic Considerations
The diagnosis of low serum creatinine levels should take into account the patient's medical history, physical examination, and laboratory results. The Kidney Disease: Improving Global Outcomes organization clinical practice guidelines define acute kidney injury (AKI) by either an increase in serum creatinine by 0.3 mg/dL within 48 hours, an increase in serum creatinine to 1.5-fold from baseline that presumably has occurred within the previous 7 days, or urine volume <0.5 mL/kg/h for 6 hours 1.
Management
The management of low serum creatinine levels depends on the underlying cause. If the cause is related to decreased muscle mass or malnutrition, the patient may require nutritional support or physical therapy to improve muscle mass. If the cause is related to liver disease, the patient may require treatment for the underlying liver condition. If the cause is related to pregnancy, the patient may require close monitoring of their kidney function and blood volume. If the cause is related to certain medications, the patient may require alternative medications or dose adjustments 1.
From the Research
Causes of Low Serum Creatinine Levels
- Low muscle mass is a primary cause of low serum creatinine levels, as creatinine is a byproduct of muscle metabolism 2, 3, 4, 5
- Malnutrition and muscle wasting can also lead to low serum creatinine levels, particularly in critically ill patients 4, 5
- Chronic kidney disease (CKD) can affect creatine production, leading to low serum creatinine levels, especially in patients with advanced CKD stages 6
- Age, sex, and body mass index can also influence serum creatinine levels, with older adults and those with lower body mass index tend to have lower serum creatinine levels 2, 3
Relationship Between Serum Creatinine and Muscle Mass
- Serum creatinine is often used as a surrogate marker of muscle mass, as it is closely related to muscle metabolism 2, 3, 5
- Low serum creatinine levels have been associated with frailty, mortality, and poor outcomes in various patient populations, including older adults and critically ill patients 2, 4, 5
- Muscle mass-independent markers, such as cystatin C, may be useful in estimating renal function and avoiding overestimation of glomerular filtration rate (GFR) in patients with low muscle mass 3
Clinical Implications
- Low serum creatinine levels can be a predictor of mortality and poor outcomes in critically ill patients, independent of body mass index 4, 5
- Accurate assessment of muscle mass and renal function is crucial in clinical practice, particularly in patients with CKD or those at risk of muscle wasting 3, 6
- Dietary adjustments, including creatine supplementation, may be necessary to prevent creatine deficiency and related symptoms in patients with CKD 6