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Pathology testing for chronic kidney disease plays an extremely important role in the diagnosis, monitoring, and management of kidney disease. The kidneys are responsible for filtering waste, balancing fluids in the body, regulating blood pressure, creating hormones that help to produce red blood cells, and promoting bone health.
Pretty important, right?
So, it’s essential to keep these little organs working well! However, when things do go wrong, it is crucial to understand the tests and examinations available to assess kidney function. Below is a list of the key tests your doctor can provide to monitor kidney health.
Unfortunately, in some cases, KD may have already occurred before you have even developed symptoms. Due to this, anyone over the age of 50 must maintain a yearly check-up to assess overall health and assess kidney function. Individuals with an increased risk of KD should also, at the very least, have annual check-ups much earlier in life, for example, at 40 years of age.
Pathology tests provide essential information about the health of your kidneys and the nature of any underlying disease. These tests also help healthcare professionals hopefully detect KD at an early stage, identify the specific type and severity of disease, and provide treatment options that will help prevent further damage and improve patient outcomes. Understanding the different testing available is of key importance when managing kidney health.
Let’s discuss the tests and examinations available, focussing on the critical tests doctors use to diagnose and monitor KD. It is crucial to note that there is no single test that provides a complete picture; therefore, multiple tests may be needed for comprehensive evaluation. It is recommended you have several tests performed to asses kidney health, what one test may miss, another will find!
Tests may be divided into different categories;
Creatinine and BUN are two key tests used to assess kidney function and the progression of the disease. Creatinine is the waste product created by normal muscle wear and tear. Creatinine levels are checked with another kidney function marker, BUN. The two tests together indicate overall kidney function.
Normal creatinine levels can vary due to;
Dehydrated people may have higher creatinine. Serum creatinine ranges are lower for women as women have less muscle mass, which results in a lower rate of creatinine formation and excretion. BUN levels can increase during pregnancy.
Although low creatinine levels can be seen in those with low muscle mass, this is generally not considered a serious medical problem.
High, Low, & Normal Creatinine Levels: What This Blood Test Means (emedicinehealth.com)
These tests are both reliable measures of kidney function, they are a common assessment to measure how well the kidneys filter waste products, which is one of the primary functions kidneys are required to do.
It is important to note, creatinine can increase after a big meal or a heavy weight session and as stated, levels are impacted by dehydration. Therefore, this test is not as reliable as GFR as an overall kidney function reading.
Procedure: A simple blood test is all that is required.
The GFR test measures how well your kidneys filter waste products and excess fluids from the blood. A GFR over 90 is considered normal. AS early KD can have no symptoms, a GFR test is a precious tool to assess kidney function. This test is particularly important if you have an increased risk of KD, especially if you have diabetes.
This test is the most reliable indicator of kidney function and will dictate the stage of kidney damage. Therefore, it is used to screen for kidney damage or determine a patient’s progression and stage of kidney damage.
GFR can be measured by injecting a tracer substance, which needs to be filtered by the kidneys. The concentration in the blood and urine is measured over time. Depending on the results of this test, patients can be placed into five separate categories.
eGFR is an estimation of your GFR. It is an estimated value calculated using a formula that takes age, gender, race and serum creatinine levels into account. It can also be calculated using your cystatin C level instead of or in addition to your blood creatinine level. When looking at the eGFR, the higher the number, the better. In general, an eGFR lower than 60 is a sign your kidneys may not be working as well as they could be. A reading lower than 15 is a marker of kidney failure.
This test is only accurate in stages 3-5 of kidney damage. Muscle mass can affect results as the calculation is based on an assumed muscle mass level according to age, gender, and race.
Can my GFR get better? | National Kidney Foundation
Monitoring electrolyte levels provides important information about your overall kidney function and can guide supplement and dietary recommendations. Kidney dysfunction can lead to an imbalance of electrolytes.
The main electrolytes that become an issue are;
High potassium (hyperkalemia) is of most concern.
Testing electrolytes is an integral part of managing and evaluating kidney health. It also helps assess the effectiveness of treatment strategies. Looking at the status of all minerals can give us information on how they are working in balance with one another and, as described, can indicate any dietary changes or supplement prescriptions required.
Please note that some levels can be altered due to dehydration, so they may not accurately assess the blood status of a specific mineral.
The pH of the blood should be between 7.35-7.45 for metabolic processes, this test measures the alkalinity and acidity of the blood. The kidneys play a major role in maintaining the body’s pH balance. Kidney disease affects the balance of the body’s pH, mostly due to the imbalance of electrolytes. Testing pH levels can tell us whether the kidneys are under a lot of pressure, as keeping pH balance is one of their essential functions. This test is not good enough on its own to asses kidney function, it needs to be done with other testing to get a clearer picture of kidney function.
The foods we eat immediately affect blood pH, so one blood reading may not reflect what is usually happening with blood pH.
Image via [PDF] [Cystatin C and cardiovascular risk]. | Semantic Scholar
The most common method of estimating glomerular filtration rate (eGFR) is through the measurement of serum creatinine. Cystatin C is a protein made by the cells in your body. When kidney function is working well, cystatin is kept at the right level, as kidney function declines cystatin increases. This test can have discrepancies in those with a high muscle mass.
The concentration of cystatin C in the blood is inversely related to the GFR. As kidney function declines, the concentration of cystatin C in the blood increases. Measuring cystatin C levels in the blood can provide valuable information about kidney function, complementing serum creatinine.
The advantage of this test is that it can detect mild decreases in kidney function before significant damage occurs. To compare, creatinine only increases with 50% damage to the kidneys.
Non-renal factors such as inflammation, thyroid issues, corticosteroid medication, cancer, chemotherapy and aging can impact cystatin C levels regardless of kidney function. In these cases, this test may not be able to provide accurate results.
Image via Kidney Tests (Kidney Function Panel) | Chronic Portal
Blood cell counts are not only important from a diagnosis perspective, it is an important test to monitor and give an indication of overall health. It is important to monitor iron levels, as when KD develops anaemia can be an issue. The kidneys produce the hormone erythropoietin (a blood-building hormone), and this declines as the progression of disease begins to take hold. As this falls, you will find that so too do your haemoglobin levels.
Inflammation can also disrupt this reading in assessing for anaemia, however, this is a good test to monitor health and track the progression of anaemia. It also helps assess how supplementation/dietary changes impact the state of anaemia moving forward.
Human transforming growth factor beta 1 (TGF-β1), plays an essential role in regulating various cellular processes. It is particularly significant in the context of tissue homeostasis, immune regulation and the pathogenesis of diseases, including fibrosis and cancer. Renal fibrosis involves accumulating scar tissue in the kidney, leading to dysfunction. TGF-β1 is considered to play a significant role in this process.
TGF-β1 is involved in wound healing and tissue repair. It stimulates the production of extracellular matrix components such as collagen and fibronectin, which are essential for tissue regeneration. Excessive activity of TGF-β1 is seen in cancer, fibrosis, and inflammation.
TGF-b1 – Lab Results explained | HealthMatters.io
Vitamin D deficiency has been found to increase the progression of CKD. This may be due to a number of factors, including:
An important factor linked with vitamin D deficiency in those with kidney disease is reduced kidney function, as the final stage of converting vitamin D into its active form, calcitriol, occurs in the kidneys. So, when kidney function declines, there is a progressive decline in the activity of 1-alpha hydroxylase, the enzyme required to convert vitamin D to its active form.
Depleted vitamin D levels have significant implications for bone health, mineral metabolism, the immune system and overall health in those with KD.
Vitamin D also helps regulate phosphorus levels in the blood, which is also important for bone health.
Part of treating KD includes monitoring phosphorus levels. High phosphate levels are often seen in kidney damage. If your kidneys are not functioning well and you are not undergoing dialysis treatment, your kidneys may be having trouble removing phosphorus from your body. As phosphorus and calcium work together and due to the individual needs of those with KD, it is essential to monitor this mineral. Testing helps monitor the progression of CKD and the effectiveness of treatments used to control phosphorus levels.
High blood phosphate can lead to low blood calcium. This increases the risk of weakened bones and osteoporosis.
This can be performed as a simple blood test or as a 24-hour urine collection.
The parathyroid glands and kidneys are closely linked through their role in regulating calcium and phosphorus balance. The progressive decline in kidney function due to CKD disrupts the balance of calcium, phosphorus and PTH regulation. As kidney function continues to decline, the kidneys’ ability to convert vitamin D to its active form is impaired. As a result, there is decreased absorption of calcium from the intestines and reduced calcium reabsorption in the kidneys. These changes trigger a response from the parathyroid glands, leading to excessive secretion of PTH, a condition known as secondary hyperparathyroidism.
Elevated PTH levels contribute to the imbalance of calcium and phosphorus levels. Secondary hyperparathyroidism contributes to vascular calcification due to calcium deposit in blood vessels. This process can increase the risk of cardiovascular events and complications.
Secondary hyperparathyroidism is a key factor in the development of renal osteodystrophy, a condition characterized by bone abnormalities and increased fracture risk.
PTH testing is a key diagnostic and monitoring tool when dealing with CKD.
Anion gap is a measurement used to check for the acid-base balance of your blood and/or an electrolyte imbalance. It is a calculation of the difference between the amounts of negatively charged electrolytes, such as chloride and bicarbonate and the positively charged electrolytes, such as sodium, in the blood.
The anion gap is calculated based on the results of individual electrolyte blood tests, which are commonly used in routine blood work as follows-
Causes of a high anion gap include;
Anion Gap Blood Test: What It Is, Purpose, Risks & Results (clevelandclinic.org)
Ultrasound is best utilised to examine for any urinary obstruction, such as kidney stones. This is a safer option to other techniques because it does not use radiation. However, deep structures may not be able to be viewed in obese patients.
This test involves taking a small sample of the organ via a needle and then having it analysed. It is used to find the cause of kidney disease and to see if the cause is reversible (from a Western medical viewpoint). A biopsy can sometimes detect the cause of kidney damage, whereas other methods are unsuccessful.
Please note this can be a painful procedure. Also, in cases of kidney malignancies, having a biopsy could potentially cause cancer to spread.
I hope this serves as a valuable reference for you moving forward.
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