Creatinine (sCR)

Serum creatinine testing is valuable in assessing kidney function and maternal health. In this article, I'll discuss the physiological changes that impact serum creatinine levels, as well as research on using creatinine as a biomarker of pregnancy health and common causes of abnormal ranges.  

Creatinine Testing

The serum creatinine (sCR) test measures the creatinine concentration in the blood. Creatinine is a waste product that muscle metabolism releases into the bloodstream. The level of creatinine in the blood is used as an indicator of how effectively the kidneys are functioning; it is considered more accurate than the estimated glomerular filtration rate (eGFR).

Creatinine is a small molecule and is easily filtered through the glomerulus of the kidneys. Once in the renal tubules, the filtrate (which contains creatinine) flows through the renal tubular system. While the renal tubules reabsorb many substances from the filtrate, creatinine is typically not reabsorbed to a significant extent. This means that most of the creatinine remains in the tubules and ultimately ends up in the urine. In addition to filtration and limited reabsorption, the renal tubules also play a role in actively secreting creatinine. The proximal convoluted tubule secretes creatinine from the blood into the tubules. This secretion process helps to ensure that any creatinine not effectively filtered in the glomerulus or reabsorbed in the tubules is efficiently removed from the body.

Creatinine in Pregnancy

Creatinine clearance increases approximately 50% during pregnancy. With this, there is a rapid decrease from prepregnancy to 24 weeks, peaking between 15 and 21 weeks of gestation with a 23.2% reduction in serum creatinine. 

After 25 weeks of gestation, creatinine levels increase slightly. 

​Creatinine levels increase postpartum as the glomerular filtration returns to normal. 

Elevations in blood urea nitrogen (BUN) can indicate earlier kidney dysfunction, in comparison to serum creatinine. Creatinine is often not affected until over half of kidney nephrons are affected by disease. ​Serum creatinine remains the most used biomarker of kidney function despite its known limitations: serum creatinine level is influenced by multiple factors such as age, sex, muscle mass, muscle metabolism, diet, medications, and hydration status.

High Creatinine in Pregnancy

Serum creatinine levels can be nearly 13 times higher in preeclamptic women.
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Serum creatinine is usually less than 0.8 mg/dL during pregnancy; higher levels suggest intravascular volume contraction or renal involvement in preeclampsia. [7] 

Most Common Causes of High Creatinine in Pregnancy

• Hypothyroidism
• Renal Damage
• Kidney Stones/Infections
• Dehydration
• Certain Medications (NSAIDs, antibiotics)
• Mycotoxin Exposure
• High Protein Diet
• Low Progesterone
• Autoimmune Disease
• High Muscle Mass

Low Creatinine in Pregnancy

​There is limited data on the application of this indice in pregnancy.

Most Common Causes of Low Creatinine in Pregnancy

• Advanced Maternal Age
• Malnutrition
• Hyperthyroidism
• Reduced Muscle Mass
• Sedentary Lifestyle
• Low Protein Diet

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Medical Disclaimer:
This content is for educational purposes only and is intended for licensed medical professionals. It is based on current research, subject to change, and not intended to diagnose, treat, or prevent any medical condition. This information does not replace consultation with a qualified healthcare provider. Seek professional medical evaluation and treatment from a licensed provider. Use of this information is at your own risk.​

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