Nephrologist: kidney diseases

A nephrologist is a physician who specializes in the prevention, diagnosis, and treatment of kidney disease at all stages, from early impairment to end-stage renal failure, including preparation for renal replacement therapy and post-transplant management. Their goal is to slow the loss of kidney function, reduce cardiovascular risks, and maintain the patient's quality of life. [1]

A nephrologist's work includes assessing symptoms and risk factors, ordering laboratory and imaging tests, interpreting results, and selecting personalized treatment. Management often requires a team approach involving a physician, cardiologist, endocrinologist, nutritionist, and other specialists. [2]

A nephrologist oversees patients before and after transplantation, managing immunosuppression, preventing complications, and long-term follow-up. They also manage treatment during dialysis and educate patients on how to participate consciously in their treatment. [3]

A separate area of expertise is pediatric nephrology and pregnancy issues in chronic kidney disease. These situations require more frequent monitoring, fine-tuning of therapy, and coordination with an obstetrician-gynecologist and pediatrician. [4]

When to see a nephrologist

Reasons for consultation include changes in a general urine analysis, the presence of protein or blood, edema, foam in the urine, persistently elevated blood pressure, decreased urine output, lower back pain with fever, as well as unexplained fatigue and itchy skin. Early referral to a specialist reduces the risk of disease progression and cardiovascular complications. [5]

A nephrologist is mandatory if primary kidney disease is suspected, if function is rapidly deteriorating, if the diagnosis is complex, or if a kidney biopsy is necessary. A consultation is also indicated when preparing for renal replacement therapy and if the estimated glomerular filtration rate is below 30 ml per minute per 1.73 square meters. [6]

Patients with diabetes, hypertension, obesity, a family history of kidney disease, and cardiovascular disease should undergo regular screening for chronic kidney disease with an estimated glomerular filtration rate (EGFR) and urine albumin-to-creatinine ratio (UACR). Albuminuria is an early indicator of kidney damage. [7]

In acute conditions - sudden decrease in urine output, severe weakness, confusion, severe shortness of breath, chest pain, high fever with pain when urinating - immediate emergency care is required, as this may indicate acute kidney injury or a severe infection. [8]

Table 1. Common complaints and what the doctor will do

Complaint	Why is it important?	What will a nephrologist check?	First steps
Foam in the urine, swelling	Possible albuminuria and sodium retention	Urinalysis, albumin to creatinine ratio, blood biochemistry	Salt restriction, medication clarification
High blood pressure	Pressure damages the glomeruli	Home blood pressure monitoring, blood and urine tests	Selecting therapy to control blood pressure
Blood in urine	Risk of glomerular damage	Microscopy of sediment, albuminuria, ultrasound	Exclusion of urological causes, referral according to indications
A sharp decrease in urine	Sign of acute injury	Creatinine, electrolytes, ultrasound diagnostics	Discontinuation of nephrotoxic agents, restoration of volume

How does a nephrologist make a diagnosis?

The basic kit includes a complete urinalysis, quantitative assessment of albuminuria using the albumin-to-creatinine ratio in a single urine sample, and estimated glomerular filtration rate (GFR) based on creatinine using current equations without race adjustment. If there is any doubt or if the estimate is inconsistent with the clinical picture, the cystatin C rate or a combined estimate is calculated. [9]

The albumin-to-creatinine ratio is a sensitive marker of early glomerular damage. A confirmed value of 3 mg/mmol or higher is considered clinically significant. For values between 3 and 70 mg/mmol, a repeat early morning sample is recommended for verification. A value of 70 mg/mmol or higher does not require confirmation. [10]

Instrumental diagnostics include ultrasound examination of the kidneys and urinary tract to assess size, structure, and the presence of obstruction. Computed tomography and magnetic resonance imaging are performed as indicated, taking into account the safety of contrast agents in patients with reduced renal function. A kidney biopsy is performed if immune-inflammatory diseases are suspected, the course of the disease is atypical, or rapid changes are observed. [11]

A nephrologist assesses overall cardiovascular risk, anemia, mineral-bone disorders, nutrient deficiencies, and nutrition, as chronic kidney disease is a systemic condition affecting blood vessels, bones, blood, and metabolism. This determines not only treatment but also the frequency of follow-up. [12]

Table 2. Basic laboratory tests by a nephrologist

Study	What does it show?	When is it prescribed?	How to interpret
General urine analysis	Leukocytes, erythrocytes, protein, cylinders	To everyone upon initial contact and dynamically	Nitrites and leukocytes in symptoms of infection, erythrocytes in glomerular damage
Albumin to creatinine ratio	Early glomerular injury	Screening of risk groups and treatment monitoring	<3 mg per mmol is normal, 3-30 is a moderate increase, >30 is a pronounced increase
Creatinine and estimated glomerular filtration rate	Filtering function	Any suspicion of damage	Glomerular filtration rate categories from G 1 to G 5
Cystatin C	Clarification of the true function	Inconsistency with clinical presentation, extreme body weight values, advanced age	Helps confirm chronic kidney disease

How is chronic kidney disease classified?

Chronic kidney disease is defined as a persistent decline in kidney function for more than three months or evidence of structural damage with clinical consequences. The assessment is based on two axes: glomerular filtration rate and albuminuria category. This approach standardizes diagnosis and prognosis. [13]

The glomerular filtration rate is divided into five categories of decreasing function from G 1 to G 5. This helps determine risks, frequency of monitoring and the timing of preparation for renal replacement therapy. [14]

Albuminuria categories from A1 to A3 reflect the degree of glomerular filter damage. The higher the albuminuria, the higher the risk of progression and cardiovascular events, even with a relatively preserved glomerular filtration rate. [15]

The combination of glomerular filtration rate and albuminuria categories determines individual risk and the intensity of treatment and monitoring. This risk-based approach underlies current recommendations. [16]

Table 3. Classification by glomerular filtration rate

Category	Glomerular filtration rate, ml per minute per 1.73 square meters	Clinical interpretation
G 1	≥ 90	Normal or elevated in the presence of other signs of damage
G 2	60-89	Slightly reduced in the presence of other signs of damage
G 3a	45-59	Moderately reduced
G 3b	30-44	Significantly reduced
G 4	15-29	Severe decline
G 5	< 15	Renal failure

Table 4. Albuminuria categories

Category	Albumin to creatinine ratio, mg/g	Albumin to creatinine ratio, mg/mmol	Description
A 1	< 30	< 3	Normal or slightly elevated
A 2	30-300	3:30	Moderately elevated
A 3	> 300	> 30	Highly elevated

Table 5. Assessment of the risk of progression by a combination of the glomerular filtration rate and albuminuria categories

Combination of categories	Prognostic risk	Surveillance tactics
G 1-G 2 with A 1	Short	Periodic monitoring and correction of risk factors
G 1-G 2 with A 2, or G 3a with A 1	Moderate	Regular monitoring, nephroprotective pharmacotherapy
G 3b with A 2, or G 3a with A 3	High	Intensive nephroprotection, frequent monitoring and consultation with a nephrologist
G 4-G 5 or A 3 at any speed	Very tall	Nephrologist supervision, preparation for renal replacement therapy

Nephroprotection: goals and first steps

Basic goals include blood pressure control, reduction of albuminuria, smoking cessation, salt restriction, and weight management. Standardized blood pressure measurements are preferred, and systolic pressure should be reduced to guideline targets if tolerated and safe. [17]

Diet plays an independent role: sodium intake is recommended to be less than 2 g per day, equivalent to approximately 5 g of table salt, as well as individualized protein intake with the help of a clinical nutritionist. Emphasis is placed on fresh produce, and potassium and phosphorus levels are monitored as needed. [18]

It is important to avoid dehydration, excessive use of nonsteroidal anti-inflammatory drugs, and uncontrolled use of contrast agents. In case of pain, alternatives should be considered in consultation with a physician to reduce the risk of acute kidney injury. [19]

The patient is recommended age- and condition-appropriate vaccinations, regular monitoring of blood sugar levels for diabetes, lipids, anemia, and mineral-bone disorders. This combination of measures simultaneously reduces the rate of functional loss and overall cardiovascular risk. [20]

Table 6. Nephroprotection goals and daily measures

Direction	Target	Practical steps
Pressure	Lowering systolic pressure to a safe target	Home monitoring, therapy selection, salt reduction
Albuminuria	A decrease by a clinically significant amount	Optimization of therapy, control after 3-6 months
Nutrition	Sodium less than 2 g per day	Avoid adding salt and choose foods with low salt content
Smoking	Complete refusal	Smoking cessation support and programs

Drug therapy with proven benefit

Angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers reduce protein in the urine and slow the progression of chronic kidney disease. After starting or increasing the dose, creatinine and potassium are monitored for 1-2 weeks; a moderate change in creatinine is expected. Combining both groups is not recommended. [21]

Sodium-glucose cotransporter type 2 inhibitors are indicated for adults with chronic kidney disease as part of standard therapy, including those with diabetes, to slow the decline in kidney function and reduce cardiovascular risk. A number of health systems have confirmed the benefit of these drugs with an estimated glomerular filtration rate (EGFR) starting at approximately 20 ml per minute per 1.73 square meters. [22]

In patients with diabetes mellitus and persistent albuminuria despite therapy with an angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker, the addition of a nonsteroidal mineralocorticoid receptor antagonist, such as finerenone, is considered, provided potassium and glomerular filtration rate are normal. This further reduces the risk of renal and cardiovascular outcomes. [23]

The choice of hypoglycemic therapy for diabetes with chronic kidney disease includes priority classes with proven nephroprotection and cardioprotection. Current standards emphasize the role of sodium-glucose cotransporter type 2 inhibitors as first-line therapy, depending on the glomerular filtration rate, as well as the possible addition of glucagon-like peptide type 1 receptor agonists if necessary. [24]

Table 7. Main drug groups for chronic kidney disease

Group	Who is it indicated for?	Expected effect	What to control
Angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker	Albuminuria, arterial hypertension	Reduction of albuminuria, protection of glomeruli	Creatinine and potassium after 1-2 weeks
Sodium-glucose cotransporter type 2 inhibitor	Adults with chronic kidney disease, including diabetes	Slower decline in function, fewer hospitalizations	Volume, risk of genital infections
Nonsteroidal mineralocorticoid receptor antagonist	Diabetes with albuminuria during basic therapy	Additional nephro- and cardioprotection	Potassium, creatinine
Diuretics and other antihypertensive agents	Control of pressure and swelling	Reducing the risk of progression and events	Electrolytes, symptoms

Acute conditions: what is considered urgent?

Acute kidney injury is a rapid, deterioration in kidney function within days, characterized by an increase in creatinine and changes in urine output. Common causes include dehydration, infection, drug effects, and urinary tract obstruction. Initial steps include addressing the underlying cause, discontinuing potentially nephrotoxic drugs, and volume restoration. [25]

Nonsteroidal anti-inflammatory drugs (NSAIDs) can cause acute kidney injury, especially in the elderly, with reduced kidney function, dehydration, heart failure, or when taken concomitantly with an angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker (ARB) and a diuretic. Self-medication with such drugs without consulting a doctor is not recommended. [26]

During pregnancy, the use of nonsteroidal anti-inflammatory drugs after the twentieth week carries a risk to the fetus due to the effect on the kidneys and the volume of amniotic fluid; such drugs should be avoided unless strictly indicated and under specialist supervision. [27]

If signs of obstruction, sepsis, persistent hyperkalemia, a sharp drop in glomerular filtration rate, increasing dyspnea, or severe uremic symptoms occur, emergency medical care and possibly hospitalization are required. [28]

Table 8. Red flags requiring urgent action

Situation	What to do	For what
A sharp decrease in urination	Go to emergency room immediately	Risk of acute injury
High temperature and pain when urinating	Urgent assessment and treatment	Risk of sepsis and obstruction
Persistent hyperkalemia according to tests	Emergency correction	Risk of arrhythmia
Combination of painkillers, dehydration	Stop and replace fluids under control	Prevention of functional decline

When is a nephrologist absolutely necessary?

Current guidelines recommend referral to a nephrologist in cases of persistently high albuminuria, markedly reduced function, or a rapid decline in filtration rate, as well as resistant hypertension and difficult-to-treat concomitant disorders such as anemia or mineral-bone disorders. If the estimated risk of terminal failure within five years is 3% to 5%, consultation is also advisable. [29]

Classic referral criteria include an albumin-to-creatinine ratio of 70 mg/mmol or greater, the combination of significant albuminuria greater than 30 mg/mmol with painless blood in the urine, a persistent decrease in filtration rate of 25% or more to a more severe category, a decrease of 15 ml/min/1.73 square meters per year, and less than 30 ml/min/1.73 square meters.[30]

Children and adolescents with signs of chronic kidney disease, pregnant women with chronic kidney disease, or those with severe albuminuria also require specialist consultation. This allows for timely treatment adjustments and safe monitoring. [31]

In cases of diagnostic uncertainty, suspicion of an immune-inflammatory lesion, or the need for a kidney biopsy, the decision is made by a nephrologist, taking into account the risks, benefits, and alternatives. [32]

Table 9. Criteria for referral to a nephrologist

Criterion	Threshold	Comment
Albumin to creatinine ratio	≥ 70 mg/mmol	Direction independent of filtration speed
Albuminuria greater than 30 mg/mmol and painless hematuria	Yes	Rule out urological causes
Decrease in filtration rate	< 30 ml per minute per 1.73 square meters	Mandatory consultation
Rapid decline of function	≥ 15 ml per minute per 1.73 square meters per year or ≥ 25% with category transition	Intensive diagnostics and correction

Diet and lifestyle for kidney disease

Limiting sodium to less than 2 g per day helps control blood pressure and swelling. It's helpful to read food labels, avoid adding salt, and choose fresh foods over processed ones. Protein, potassium, and phosphorus intake are adjusted individually with the help of a nutritionist, taking into account the stage of the disease and any associated conditions. [33]

A diet emphasizing vegetables, fruits, whole foods, healthy fats, and adequate fiber supports metabolic health. For those prone to hyperkalemia, food types and portions should be carefully selected, and for those with mineral-bone disorders, excess phosphorus should be limited, especially from supplements and carbonated beverages. [34]

The drinking regimen should be discussed with a physician: in cases of edema, heart failure, and low filtration rate, fluid restriction is sometimes required, while in cases of a tendency toward dehydration, adequate intake is recommended. Going to extremes on your own is undesirable. [35]

Moderate-intensity physical activity, smoking cessation, and weight control complement drug therapy and improve prognosis. These are as important components of therapy as medications, and their effect is additive with drug therapy. [36]

Table 10. Dietary guidelines for chronic kidney disease

Component	Recommendation	Note
Salt	Less than 2 g of sodium per day	About 5 g of table salt
Protein	Individually by stage	With the participation of a nutritionist
Potassium	Individually	Correction of hyperkalemia
Phosphorus	Limiting excess	Avoid phosphate additives

Preparing for your visit and what to bring

It's helpful to bring a blood pressure diary with dates and times of measurements, a list of all medications and supplements with dosages, recent test results, and a list of your questions. This saves time and helps tailor treatment more precisely. [37]

Before testing the albumin-to-creatinine ratio, an early morning sample is preferred, and if the result is between 3 and 70 mg/mmol, a repeat test is recommended. This improves diagnostic accuracy. [38]

If you are taking painkillers, especially nonsteroidal anti-inflammatory drugs (NSAIDs), be sure to tell your doctor. Together, you can develop a safer pain management strategy. [39]

If you have diabetes and chronic kidney disease, discuss your blood sugar and blood pressure control goals ahead of time to create a comprehensive plan that includes medications that protect your kidneys and heart. [40]

Brief summary

A nephrologist is a key specialist in the early detection and slowing of kidney disease progression. The modern approach is based on assessing glomerular filtration rate and albuminuria, blood pressure monitoring, a sodium-restricted diet, proven medications, and timely referral to a specialist based on clear criteria. This comprehensive approach reduces the risk of progression to renal failure and cardiovascular events. [41]