Evaluation of any biomarker or biomarker ratio requires a bit of investigation to find out which biomarker is trending high or low, and why.
In this case, the reason for the increased BUN:Creatinine Ratio is that the BUN is above optimal and creatinine is below optimal. With an elevated BUN, you need to investigate the possibility of dehydration, a high protein diet, etc.
The creatinine trending low and being below optimal could be due to reduced muscle mass, sarcopenia, and debilitation.
Kidney dysfunction is less likely because the creatinine is trending low. It would be important to evaluate the eGFR to confirm that renal clearance/function is good.
Review of medical history is imperative to assess renal function over time, cardiovascular status, causes of muscle loss, etc.
High BUN:Creatinine ratio may indicate transient kidney dysfunction, especially above 20 (Raymond 2021). Temporary non-renal causes of an increased ratio include excess protein intake, GI bleeding, catabolic states such as fever or burns), dehydration, shock, congestive heart failure, or urinary tract obstruction (Hosten 1990).
An elevated ratio is also associated with increased risk of coronary artery disease in type 2 diabetics (Liu 2022), mortality from myocardial infarction and acute heart failure (Qian 2019), poorer outcomes in those with congestive heart failure (Tolomeo 2023).and increased severity and mortality from COVID-19 (Ok 2021).
A BUN:Creatinine ratio above 15 was also associated with acute ischemic stroke due to venous thromboembolism caused by dehydration (Kim 2017), as well as poor outcomes in acute ischemic stroke (Schrock 2012).
High levels of BUN are associated with renal dysfunction, dehydration, excess protein intake, GI bleeding, shock, burns, heart failure, and myocardial infarction, as well as with certain medications, including allopurinol, diuretics, antibiotics, and aspirin (Pagana 2021). Elevated BUN is observed in acute pancreatitis and may predict severity as well as mortality from the condition (Dai 2022, Lin 2017, Wu 2011). Other catabolic processes, such as fever and infection, can increase BUN as well (Hosten 1990).
Low creatinine levels are associated with debilitation, decreased muscle mass, muscular dystrophy, and myasthenia gravis (Pagana 2021). A low serum creatinine associated with reduced muscle mass may increase the risk of type 2 diabetes (Harita 2009, Hu 2019).
Hosten, Adrian O. “BUN and Creatinine.” Clinical Methods: The History, Physical, and Laboratory Examinations, edited by H Kenneth Walker et. al., 3rd ed., Butterworths, 1990.
Kim, Hoon et al. “Elevated Blood Urea Nitrogen/Creatinine Ratio Is Associated with Venous Thromboembolism in Patients with Acute Ischemic Stroke.” Journal of Korean Neurosurgical Society vol. 60,6 (2017): 620-626. doi:10.3340/jkns.2016.1010.009
Liu, Feng et al. “Elevated blood urea nitrogen-to-creatinine ratio increased the risk of Coronary Artery Disease in patients living with type 2 diabetes mellitus.” BMC endocrine disorders vol. 22,1 50. 28 Feb. 2022, doi:10.1186/s12902-022-00954-3
Ok, Fesih et al. “Predictive values of blood urea nitrogen/creatinine ratio and other routine blood parameters on disease severity and survival of COVID-19 patients.” Journal of medical virology vol. 93,2 (2021): 786-793. doi:10.1002/jmv.26300
Pagana, Kathleen Deska, et al. Mosby's Diagnostic and Laboratory Test Reference. 15th ed., Mosby, 2021.
Qian, Hao et al. “Predictive value of blood urea nitrogen/creatinine ratio in the long-term prognosis of patients with acute myocardial infarction complicated with acute heart failure.” Medicine vol. 98,11 (2019): e14845. doi:10.1097/MD.0000000000014845
Raymond, Janice L., et al. Krause and Mahan's Food & the Nutrition Care Process. Elsevier, 2021.
Salvador, López Giacoman et al. “A low BUN/creatinine ratio predicts histologically confirmed acute interstitial nephritis.” BMC nephrology vol. 24,1 75. 27 Mar. 2023, doi:10.1186/s12882-023-03118-0
Shen, Song et al. “The blood urea nitrogen/creatinine (BUN/cre) ratio was U-shaped associated with all-cause mortality in general population.” Renal failure vol. 44,1 (2022): 184-190. doi:10.1080/0886022X.2022.2030359
Schrock, Jon W et al. “Elevated blood urea nitrogen/creatinine ratio is associated with poor outcome in patients with ischemic stroke.” Clinical neurology and neurosurgery vol. 114,7 (2012): 881-4. doi:10.1016/j.clineuro.2012.01.031
Tolomeo, Paolo et al. “Independent prognostic importance of blood urea nitrogen to creatinine ratio in heart failure.” European journal of heart failure, 10.1002/ejhf.3114. 20 Dec. 2023, doi:10.1002/ejhf.3114
Zia Ziabari, Seyyed Mahdi et al. “Blood Urea Nitrogen to Creatinine ratio in Differentiation of Upper and Lower Gastrointestinal Bleedings; a Diagnostic Accuracy Study.” Archives of academic emergency medicine vol. 7,1 e30. 2 Jun. 2019