Nephrologists rely on a layered set of tests, starting with routine blood and urine work and escalating to imaging, biopsy, and specialized panels depending on what the initial results reveal. The backbone of every nephrology workup is a handful of blood markers that estimate how well your kidneys filter waste, paired with urine tests that detect protein or blood that should not be there. Beyond these staples, the specific tests a nephrologist orders depend heavily on whether the concern is a sudden kidney injury, slowly progressing chronic disease, a transplant evaluation, or something rarer like an inherited condition.
Blood Tests That Measure Kidney Filtration
The single most common test in nephrology is serum creatinine, a waste product your muscles produce at a fairly steady rate. Healthy kidneys clear creatinine efficiently, so a rising level signals that filtration is slipping. A nephrologist rarely looks at creatinine in isolation, though. Creatinine feeds into an equation that produces your estimated glomerular filtration rate, or eGFR, which is the number that actually stages kidney disease. Blood urea nitrogen, or BUN, is usually drawn at the same time. BUN is considered less precise because diet, hydration, and liver function all nudge it around, but reviewing creatinine and BUN together gives clinicians a fuller picture than either value alone.1Emergency Medicine Clinics of North America. Blood Urea Nitrogen and Creatinine
For some patients, creatinine-based estimates are unreliable. People with unusually high or low muscle mass, older adults, and those with certain dietary patterns can have creatinine levels that mislead. In those situations, a nephrologist may add cystatin C, a small protein produced by virtually all cells in the body. Cystatin C is less affected by muscle mass and has been established as an early and accurate marker of chronic kidney disease when creatinine falls short.2PubMed Central. Cystatin C as a biomarker of chronic kidney disease: latest developments Current guidelines recommend cystatin C specifically when creatinine-based eGFR is not thought to be accurate enough for clinical decision-making.3PubMed. Discordances Between Creatinine- and Cystatin C-Based Estimated GFR and Adverse Clinical Outcomes in Routine Clinical Practice
That said, cystatin C is not a universal upgrade over creatinine. A large study tracking patients with moderate chronic kidney disease found that adding cystatin C to the filtration-rate equation improved accuracy only slightly and did not help detect disease progression any better.4Health Technology Assessment. Accuracy of glomerular filtration rate estimation using creatinine and cystatin C for identifying and monitoring moderate chronic kidney disease So your nephrologist is likely to order cystatin C selectively rather than on every visit.
What Urine Tests Reveal
A standard urinalysis checks for blood, protein, glucose, and signs of infection using a dipstick, sometimes followed by examination under a microscope. Microscopy can reveal things automated dipstick machines miss, such as pathological casts (tiny cylindrical clumps that form in kidney tubules), unusual crystals, and misshapen red blood cells that point toward glomerular bleeding rather than a lower urinary tract source.5PubMed Central. Diagnostic Utility of Urine Microscopy in Kidney Diseases When a nephrologist specifically requests urine microscopy rather than relying on an automated analysis, it is usually because they suspect a disease process that leaves behind those telltale signs.
Beyond a simple dipstick, nephrologists pay close attention to how much protein leaks into urine. The most convenient screening tool is a spot urine albumin-to-creatinine ratio, or ACR. Because collecting urine over a full 24 hours is inconvenient and error-prone, the ACR from a single sample estimates the same information. In diabetic kidney disease, the random-sample albumin-to-creatinine ratio has shown strong sensitivity and specificity compared with a full 24-hour collection, making it a practical alternative.6PubMed Central. Quantitative Micro-albuminuria Assessment from ‘Random Voided Urinary Albumin: Creatinine Ratio’ Versus ’24 hours Urinary Albumin Concentration’ for Screening of Diabetic Nephropathy The correlation between a spot ACR and a full 24-hour proteinuria measurement remains strong across different stages of kidney disease and different types of glomerular disease.7Nephrology Dialysis Transplantation. Correlation Between 24-H Proteinuria and Spot Urine Albumin-Creatinine Ratio in Biopsy-Proven Glomerular Diseases
There are limits, though. When proteinuria is very heavy, the correlation weakens. And in non-diabetic kidney disease, a total protein-to-creatinine ratio may actually outperform albumin-to-creatinine ratio at predicting how much total protein is being lost, because some kidney diseases spill proteins other than albumin.8Nephrology Dialysis Transplantation. Assessing proteinuria in chronic kidney disease: protein–creatinine ratio versus albumin–creatinine ratio Your nephrologist will choose between these tests based on the suspected diagnosis.
Imaging the Kidneys
Ultrasound is the workhorse imaging tool in nephrology. It requires no radiation, no contrast dye, and it gives a quick read on kidney size, shape, and whether urine is backing up due to an obstruction. Beyond diagnosis, ultrasound also guides hands-on procedures like kidney biopsy and the placement of dialysis catheters.9PubMed Central. Renal relevant radiology: use of ultrasound in kidney disease and nephrology procedures Shrinkage of both kidneys on ultrasound, for example, is a classic sign that chronic damage has been building for a while, while a single enlarged kidney with a dilated collecting system points to an acute obstruction like a stone.
CT scans and MRI come into play when ultrasound cannot provide enough detail, such as mapping a complex cyst, evaluating a suspected tumor, or planning for transplant surgery. The concern with CT is contrast dye, which can temporarily stress the kidneys. MRI uses gadolinium-based contrast instead, and while that sounds safer, gadolinium carries its own risk in people with very low kidney function. In patients with severely reduced filtration, conditions like acid-base disturbances and high phosphorus levels can increase the amount of free gadolinium circulating in the body, raising the risk of toxicity.10PubMed Central. Gadolinium-Based Contrast Media Nephrotoxicity in Kidney Impairment
The feared complication historically was nephrogenic systemic fibrosis, a severe scarring condition. With newer gadolinium agents, however, that risk has dropped dramatically. A joint consensus from the American College of Radiology and the National Kidney Foundation noted zero cases of nephrogenic systemic fibrosis in nearly 5,000 administrations of newer-group contrast agents to patients with advanced kidney disease.11PubMed. Use of Intravenous Gadolinium-based Contrast Media in Patients with Kidney Disease So if your nephrologist orders an MRI with contrast despite your reduced kidney function, they have weighed the risk and judged that skipping the scan could be more harmful than doing it.
Kidney Biopsy
When blood and urine tests point to a kidney problem but cannot pin down the exact disease, a biopsy is often the only way to get a definitive answer. The procedure involves guiding a needle into the kidney, usually under ultrasound, and extracting a tiny core of tissue for examination under a microscope. It is used worldwide for investigating kidney disorders, and technical advances have made it safer and more informative than it was decades ago.12JAMA. Renal Biopsy A biopsy can distinguish between disease types that look identical on lab work, such as different forms of glomerulonephritis, lupus nephritis, or amyloidosis. The results directly change treatment: one pattern might call for immunosuppression, another for a wait-and-watch approach.
Your nephrologist will typically check clotting tests and blood pressure before the procedure and ask you to stop blood thinners in advance. The main risk is bleeding, which usually resolves on its own but occasionally requires observation or intervention. Biopsy is not ordered casually; it is reserved for situations where the tissue diagnosis will meaningfully change the management plan.
Electrolytes, Bone Minerals, and Other Routine Panels
Kidneys do far more than filter waste. They regulate potassium, sodium, calcium, phosphorus, and acid-base balance. As kidney function declines, these systems start to drift. A nephrologist routinely orders a comprehensive metabolic panel that captures sodium, potassium, bicarbonate, calcium, and phosphorus. Low bicarbonate can signal metabolic acidosis, a common complication of advanced kidney disease that accelerates further kidney damage if left untreated.
Parathyroid hormone, or PTH, is another test that appears on most nephrology panels once kidney disease reaches a moderate stage. Failing kidneys produce less active vitamin D, which causes calcium to drop and stimulates the parathyroid glands to overproduce PTH. Over time this leads to weakened bones and vascular calcification. Tracking PTH alongside calcium, phosphorus, and vitamin D levels helps the nephrologist manage what is broadly called chronic kidney disease–mineral and bone disorder.
A complete blood count is standard as well. The kidneys produce erythropoietin, the hormone that drives red blood cell production. Declining kidney function often means declining erythropoietin, which leads to anemia. Your nephrologist may also check iron studies, ferritin, and transferrin saturation to determine whether iron deficiency is compounding the problem.
Tests for Acute Kidney Injury
When kidney function drops suddenly over hours or days rather than months, the diagnostic priorities shift. One of the first questions is whether the kidneys themselves are damaged or whether the problem is upstream, such as severe dehydration or low blood pressure reducing blood flow to the kidneys. A classic tool for sorting this out is the fractional excretion of sodium, or FENa, which measures how much sodium the kidneys are holding onto versus letting go. A meta-analysis pooling data from hundreds of patients found that using a threshold of one percent, FENa distinguishes intrinsic kidney injury from prerenal causes with roughly 90 percent sensitivity and 82 percent specificity.13PubMed Central. Diagnostic Performance of Fractional Excretion of Sodium for the Differential Diagnosis of Acute Kidney Injury
FENa is most useful in straightforward cases. In complex medical situations like decompensated liver disease, the picture gets murkier. One study in patients with cirrhosis found that FENa still outperformed fractional excretion of urea in distinguishing structural kidney injury from other causes, but neither test was perfect.14Journal of Clinical and Experimental Hepatology. Fractional Excretion of Sodium and Urea in Differentiating Acute Kidney Injury Phenotypes in Decompensated Cirrhosis A nephrologist interprets these numbers in context rather than relying on a single cutoff.
Newer biomarkers are entering clinical practice for detecting acute kidney injury earlier than creatinine can. A multicenter study found that a combination of two urinary markers called TIMP-2 and IGFBP7, measured just six hours after a triggering event, predicted acute kidney injury with an area under the curve of 0.85, outperforming creatinine at that early time point. Urinary NGAL and plasma cystatin C also showed strong early detection performance.15Journal of Neonatal Surgery. Novel Biomarkers for Early Detection of Acute Kidney Injury These are not yet universally ordered, but they are becoming more common in intensive care settings where catching kidney injury early can change the course of treatment.
Screening for Monoclonal Protein Diseases
Some kidney diseases are driven by abnormal proteins produced by rogue immune cells, a category broadly called monoclonal gammopathies. These include conditions like light-chain deposition disease and certain forms of amyloidosis. To screen for them, nephrologists order serum protein electrophoresis and serum free light chains. A study comparing screening strategies found that using serum protein electrophoresis combined with serum free light chain assays detected plasma cell disorders as effectively as the traditional approach that required a urine sample, potentially eliminating the need for urine protein electrophoresis in many cases.16American Journal of Clinical Pathology. Are Renal Reference Intervals Required When Screening for Plasma Cell Disorders With Serum Free Light Chains and Serum Protein Electrophoresis? If these screening tests come back abnormal, the workup typically escalates to a bone marrow biopsy and kidney biopsy to confirm the diagnosis.
Genetic Testing in Nephrology
Genetic testing in kidney disease has moved from a niche academic exercise to a clinically meaningful tool. An estimated 10 percent or more of kidney diseases in adults and as many as 70 percent of chronic kidney diseases in children have a genetic cause.17PubMed Central. Advancing Genetic Testing in Kidney Diseases: Report From a National Kidney Foundation Working Group Conditions like autosomal dominant polycystic kidney disease, Alport syndrome, and Fabry disease all have identifiable genetic signatures. A genetic diagnosis can change management, inform family screening, and sometimes make a patient eligible for targeted therapies.
Genetic testing has also revealed surprises in populations thought to have a clear explanation for their kidney disease. Among patients carrying high-risk APOL1 gene variants, which are associated with kidney disease in people of African ancestry, nearly one in ten turned out to have a concurrent and distinct genetic kidney disease when formal testing was performed.18Kidney International Reports. Prevalence of Mendelian Kidney Disease Among Patients With High-Risk APOL1 Genotypes Undergoing Commercial Genetic Testing in the United States Findings like that have pushed the field toward broader genetic testing, especially when a patient’s disease does not fit a neat clinical pattern or when family members show signs of kidney trouble.
Transplant-Related Testing
If you are being evaluated as a kidney transplant candidate or donor, the testing landscape expands considerably. Beyond the standard bloodwork, nephrologists and transplant teams order human leukocyte antigen, or HLA, typing. HLA molecules sit on the surface of your cells and help your immune system distinguish self from foreign. The closer the match between donor and recipient HLA, the lower the risk of rejection. Modern molecular typing methods have become remarkably specific, though keeping up with the rapid changes in this technology is a challenge even for specialists.19PubMed. HLA Epitope Matching in Kidney Transplantation: An Overview for the General Nephrologist
Alongside HLA typing, transplant teams perform crossmatch testing to check whether a recipient’s blood contains antibodies against the donor’s cells. A virtual crossmatch analyzes the recipient’s existing anti-HLA antibodies against the donor’s HLA type using lab data, allowing a preliminary compatibility assessment before a physical crossmatch is done.20PubMed Central. Principles of Virtual Crossmatch Testing for Kidney Transplantation A positive crossmatch, meaning the recipient has antibodies against the donor, is generally a red flag that raises the risk of hyperacute rejection. Transplant candidates with high levels of pre-formed antibodies, often from prior transfusions, pregnancies, or a previous transplant, may need desensitization protocols before they can receive a kidney.
Cardiac Markers in Kidney Patients
Heart disease is the leading cause of death in people with chronic kidney disease, so nephrologists frequently check cardiac biomarkers. The tricky part is interpretation. Cardiac troponin, the standard marker for heart attacks, runs higher in kidney patients even when nothing acute is happening to the heart. Studies report that roughly 43 to 68 percent of people with chronic kidney disease have troponin levels above the 99th percentile of the general population, and average levels climb as kidney function worsens.21PubMed Central. Cardiac Troponins in Kidney Disease That means a mildly elevated troponin in someone on dialysis does not automatically signal a heart attack the way it would in someone with normal kidneys. Nephrologists and cardiologists have to look at trends over time and combine troponin with other clinical information rather than relying on a single value.
BNP and NT-proBNP, markers commonly used to evaluate heart failure, behave similarly. They run higher in kidney disease partly because the kidneys help clear them and partly because the cardiovascular strain of chronic kidney disease genuinely elevates them. Your nephrologist may track these alongside echocardiograms to monitor fluid overload and cardiac function, but always with the understanding that the usual cutoff values need to be interpreted differently in the setting of reduced kidney filtration.
Drug Monitoring and Nephrotoxin Surveillance
Some medications are cleared through the kidneys, which means doses that are safe for someone with normal function can accumulate to toxic levels as kidneys falter. Nephrologists routinely order drug levels for medications with narrow therapeutic windows, including certain antibiotics, anticonvulsants, and immunosuppressants used in transplant patients. Tacrolimus and cyclosporine, for instance, require regular trough-level monitoring because even small shifts in blood concentration can mean the difference between rejection and toxicity.
On the flip side, nephrologists also watch for medications that damage the kidneys. Nonsteroidal anti-inflammatory drugs, certain chemotherapy agents, and some contrast dyes are well-known offenders. Identifying drug-induced kidney injury early is an active area of research, with novel biomarkers being studied to catch damage before creatinine rises.
Home Testing and Point-of-Care Devices
An emerging frontier is letting patients check their own kidney markers at home. A clinical feasibility study in kidney transplant recipients tested whether patients could use a portable device at home to measure creatinine from a fingerstick blood sample. The home creatinine results matched standard lab values closely, with all paired results classified as clinically acceptable.22PubMed Central. Patient Self-Testing of Kidney Function at Home, a Prospective Clinical Feasibility Study in Kidney Transplant Recipients Potassium measurement was less reliable, with only about two-thirds of paired results meeting clinical equivalence standards. For transplant patients who need frequent blood monitoring but live far from a clinic, home creatinine testing could reduce the burden of travel while catching rejection or drug toxicity earlier. The technology is still being refined, but it points toward a future where some routine nephrology monitoring moves out of the lab and into the living room.