Acute renal failure - Diagnosis

Laboratory and instrumental diagnostics of acute renal failure

A clinical blood test may show moderate anemia and an increase in ESR. Anemia in the first days of anuria is usually relative. It is caused by hemodilution, does not reach a high degree and does not require correction. Blood changes are typical during exacerbation of urinary tract infection. In acute renal failure, there is a decrease in immunity, as a result of which there is a tendency to develop infectious complications: pneumonia, suppuration of surgical wounds and sites of exit to the skin of catheters installed in central veins, etc.

At the beginning of the oliguria period, the urine is dark, contains a lot of protein and cylinders, its relative density is reduced. During the period of diuresis recovery, the low relative density of urine, proteinuria, almost constant leukocyturia as a result of the release of dead tubular cells and the resorption of interstitial infiltrates, cylindruria, erythrocyturia are preserved.

In patients with a high risk of developing acute renal failure, including after major operations, it is necessary to monitor creatinine levels daily. Diagnosis of acute renal failure requires determination of urea concentration, but this study cannot be used in isolation, nevertheless, this indicator characterizes the severity of catabolism. Even if acute renal failure is suspected, it is extremely important to monitor the patient's blood electrolytes and, above all, the amount of potassium. A decrease in sodium levels indicates hyperhydration.

Biochemical monitoring of liver function is important. It is necessary to conduct a study of the blood coagulation system. Acute renal failure is characterized by impaired microcirculation with the development of DIC syndrome.

ECG monitoring is necessary, as it is a good way to monitor the potassium content in the heart muscle and possible complications from the heart. In 1/4 of patients, acute renal failure may manifest as arrhythmia, up to cardiac arrest, increased muscle excitability, hyperreflexia.

General urine analysis may reveal hematuria, proteinuria. In case of symptoms of exacerbation of urinary tract infection, bacteriological urine analysis is necessary.

During the recovery period, it is necessary to determine the SCF based on endogenous creatinine.

Renal ultrasound can determine the presence of obstruction, kidney size and parenchyma thickness, and the level of blood flow in the renal veins. Isotope renography can detect asymmetry of the curves, indicating obstruction of the urinary tract.

X-ray monitoring of the chest organs is necessary. The condition of the lungs is of great importance. This primarily concerns hyperhydration of the lung tissue or nephrogenic edema, a specific clinical and radiological syndrome. At the same time, the dynamics of the heart size are monitored to exclude pericarditis. Hyperhydration of the lung tissue often serves as the main indication for urgent hemodialysis with ultrafiltration.

Correctly and timely identification of the cause of acute renal failure will allow the patient to be brought out of critical condition faster, and will also increase the likelihood of reversibility of functional disorders in the kidneys.

The diagnosis of acute renal failure is rarely difficult.

Differential diagnosis of acute renal failure

At the first stages of differential diagnostics, it is necessary to identify a possible cause of acute renal failure. It is important to differentiate prerenal and renal forms of renal failure, since the first form can quickly develop into the second. It is also necessary to distinguish the postrenal form of acute renal failure, which developed against the background of urinary tract obstruction, from renal renal failure. For this purpose, excretory urography with high doses of contrast agent, isotope renography and ultrasound are used. Retrograde ureteropyelography is used less often. Determining the size of the kidneys using ultrasound helps to distinguish acute renal failure from chronic renal failure, to identify or exclude a violation of the outflow of urine through the urinary tract.

If the patient has anuria (oliguria) with severe anemia in the absence of a source of bleeding, then this rather indicates a chronic nature of the renal syndrome. Severe anemia is not typical for acute renal failure.

It is important to determine the time of onset of anuria, the symptoms preceding it, the presence of a history of chronic renal diseases, the presence of anemia. Often, renal syndrome is the first manifestation of progressive renal disease with the development of chronic renal failure or decompensation syndrome of latent chronic renal failure. In these cases, it is always accompanied by anemia.

With the development of polyuria, the patient's condition quickly improves, despite the high concentration of nitrogen metabolites: it may even increase slightly due to intense dehydration. Usually, the development of polyuria to the maximum level takes several days or weeks. Delayed onset of polyuria or limitation of diuresis at the level of 1.0-1.5 l, instability of diuresis increase indicate, as a rule, an unfavorable general somatic status, the addition of complications in the form of sepsis or other purulent processes, the presence of an undiagnosed disease or injury.

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Differential diagnosis of anuria and acute urinary retention

For differential diagnosis of true anuria and acute urinary retention, it is necessary to ensure that there is no urine in the bladder by percussion, ultrasound, or bladder catheterization. If less than 30 ml/h of urine is excreted through a catheter inserted into the bladder, it is necessary to urgently determine the content of creatinine, urea, and potassium in the blood.

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Differential diagnosis of acute and chronic renal failure

The following allows you to quickly differentiate acute renal failure from chronic renal failure:

• study of general symptoms and anamnesis data;
• assessment of the appearance of urine;
• assessment of the dynamics of azotemia and diuresis;
• Determination of kidney size (ultrasound, X-ray)

It is also necessary to establish the form of acute renal failure (prerenal, renal, postrenal).

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Indications for consultation with other specialists

Considering the polyetiology of acute renal failure and the possibility of its occurrence in any clinical department, joint actions of doctors of various specialties are absolutely necessary in the treatment of acute renal failure.

All patients with suspected acute renal failure or an established diagnosis of "acute renal failure" are recommended to consult and undergo dynamic observation by a nephrologist, as well as specialists in detoxification and intensive care. In case of diagnosis of renal acute renal failure associated with obstruction of the renal vessels, for example, with their thrombosis, it is necessary to involve a vascular surgeon in the treatment. In the development of the renal form of acute renal failure due to exogenous intoxication, the help of toxicologists is necessary. In the case of postrenal acute renal failure, treatment and observation by a urologist is indicated.

Formulation of the diagnosis "acute renal failure"

The diagnosis of "acute renal failure" briefly expresses the essence and completeness of the entire pathological process. The main diagnosis should reflect:

• the underlying disease that caused acute renal failure;
• leading syndromes;
• complications in order of their severity.

In each case, it is necessary to determine the place of acute renal failure in the pathological process - whether it is a manifestation of the underlying disease or its complication. This has not only a formal-logical, but also a significant significance, since it characterizes the underlying pathological process.

The diagnosis of acute renal failure includes determination of:

• the underlying disease that caused acute renal failure;
• form of acute renal failure (prerenal, postrenal or renal);
• stage of the disease (initial manifestations, oliguric, diuretic or recovery).