The Basic Metabolic Panel (BMP) is used to evaluate kidney function and monitor the effects of medications such as diuretics (water pills used to control blood pressure). Glucose (blood sugar) is also a part of this panel but we will discuss that separately, next week.
The kidney is a very hard working organ. Although it comprises less than 1% of our body mass, it receives 20% of the blood flow. This is because its principle functions are to filter the blood, maintain proper chemical balance and remove toxic waste products. It also activates Vitamin D and makes hormones that increase blood pressure and stimulate red blood cell production.
The rate at which the kidney filters the blood is known as the GFR (glomerular filtration rate). This is a calculation which is divided by one’s age. Therefore as we get older, the value decreases. Normal values should be over 90 ml/min for young adults and over 60 ml/min for adults over 50 years old. Decreases in the GFR indicate kidney dysfunction which can be due to many things including medications, contrast dyes, inflammation, polycystic disease, etc. However, the two biggest causes of kidney dysfunction are long-standing high blood pressure and diabetes.
In general, kidney functions are assessed by measuring the balance of sodium (Na), potassium (K), chloride (Cl), bicarbonate (CO2), blood urea nitrogen (BUN) and creatinine (Cr) in the blood. These chemicals affect the normal function of every cell in the body and are closely regulated. Small changes in their values may have dire effects on cellular function and can result in death.
Sodium or salt is the major electrolyte in the blood. Normal values are in the range of 135 to 145 meq/L. If values get too high, it can affect blood pressure and in the extreme may alter brain function. Low values are equally detrimental and are generally caused by medications like diuretics. Muscle cramps and lightheadedness are frequent symptoms of low sodium.
Potassium is the electrolyte which is most abundant inside the cell. Therefore serum levels of this chemical are low in comparison to sodium. Normal values are in the range of 3.5 to 5.0 meq/L. Large scale cell damage may cause significant increases in blood potassium levels. These changes may affect the electrical activity of the heart resulting in irregular beats or death.
Bicarbonate is the body’s buffering chemical as it maintains the correct acid/base (pH) balance of the blood. The chemical reactions of the body depend on the blood being close to neutral. Although shifts to the acid side are tolerated better than shifts to the basic side, either shift may affect the ability of the heart to beat. Normal values are in the range of 21 to 30 mg/dl.
Increased levels of CO2 may indicate dehydration or accumulated carbon dioxide levels which may occur with emphysema. Decreased levels of CO2 indicate metabolic acidosis and may be due to uncontrolled diabetes, severe infections, kidney disease, etc.
Blood urea nitrogen and creatinine are both products of protein breakdown. They are almost exclusively eliminated from the body by the kidney. If the BUN is allowed to accumulate in the blood, it crosses into the brain initially causing confusion then ultimately coma and death. Blood levels of BUN and Cr are also good indicators of kidney function. Increased values suggest kidney damage. Normal values for BUN range from 10 to 20 mg/dl and for Cr from 0.5 to 1.2 mg/dl.
Healthy Habits for the Kidney:
- Drink 6-8 glasses of water daily. This is particular important for people who are dieting as it helps to flush out the waste products of fat breakdown (called ketones).
- Limit the dose and duration of anti-inflammatories such as aspirin, Advil and Aleve. Use the lowest effective dose. These medications can affect kidney function.
- Keep your blood pressure under control. Aim for values under 120/80 mm Hg.
- Keep blood sugar in the normal range as sugars may clog the kidney filtration system and reduce GFR.
- Reduce salt consumption, as retention of salt and water causes increased blood volume, higher blood pressure and more work for the kidney.
Next week: Understanding Your Blood Work Part II: Glucose