Urinalysis above or below normal: causes in athletes and what to do

“Protein in the urine”, “erythrocytes”, “high specific gravity” — such entries appear often on an athlete's form and are frightening. However, a significant part of these deviations is a temporary response to training or dehydration. Others, conversely, may be the first signal of kidney damage, rhabdomyolysis, or a metabolic disorder. The editorial team examines the most frequent deviations in a urinalysis and the logic of action for each of them.

Protein in the urine

A small amount of protein in the urine after intense training is a well-known physiological response. It is linked to a change in the permeability of the glomerular filter and saturation of tubular reabsorption during load. Such proteinuria usually disappears within 24–48 hours.

Temporary proteinuria is also caused by fever, dehydration, severe stress, and cold. A separate variant is orthostatic proteinuria, when protein appears only in an upright position, which occurs in young people and is usually benign.

Persistent proteinuria in morning urine collected after several days without training requires further workup. For an accurate assessment, the albumin/creatinine or protein/creatinine ratio in a spot urine sample is determined, as recommended by the KDIGO guidelines.

Among athletes, a separate risk group is those who use anabolic steroids: the development of focal segmental glomerulosclerosis with marked proteinuria has been described. Persistent protein in the urine in such a situation is a reason for an immediate nephrologist consultation.

Blood and myoglobin in the urine

A positive reaction to blood on a test strip may mean three different things: erythrocytes, free hemoglobin, or myoglobin. Microscopy helps distinguish them: if there are no erythrocytes in the sediment while the strip is positive, hemoglobin or myoglobin is likely.

Hematuria after exercise is a frequent finding in runners, cyclists, and players of contact sports. It usually disappears within a few days. The AUA/SUFU guideline on microhematuria defines it as 3 or more erythrocytes per high-power field on microscopy and recommends assessing risk factors before a urological examination.

Myoglobinuria is a much more serious situation. It indicates massive muscle damage, that is, rhabdomyolysis. The urine becomes dark, the color of tea or cola, and severe pain and weakness in the muscles appear. This is an emergency, since myoglobin can damage the kidneys.

If hematuria persists after rest, especially in older people, smokers, or those with pain, it requires examination by a urologist or nephrologist to rule out stones, infections, and diseases of the kidneys and bladder.

Specific gravity, ketones, and glucose

High urine specific gravity (above 1.020–1.030) in an athlete most often means inadequate hydration. This is characteristic of training in the heat, cutting weight before competitions, and insufficient drinking on days with several training sessions.

Persistently low specific gravity (around 1.005 and below) usually indicates a large fluid intake. However, persistently dilute urine together with thirst and frequent urination may indicate impaired concentrating function of the kidneys or endocrine disorders and requires checking.

Ketones in the urine are expected with a low-carbohydrate diet, prolonged fasting, and a marked energy deficiency. For an athlete who is not deliberately restricting carbohydrates, ketonuria may be a sign of inadequate nutrition and part of the RED-S picture.

Glucose in the urine is not detected in a healthy person. Its appearance most often indicates an elevated blood sugar level and requires a glucose test and glycated hemoglobin. Ketones together with glucose in the urine are an alarming combination that requires immediate medical evaluation.

Leukocytes, nitrites, and other findings

Elevated leukocytes in the urine together with positive nitrites most often indicate a bacterial urinary tract infection. Characteristic symptoms are burning during urination, frequent urges, and lower abdominal pain. The diagnosis is confirmed by a urine culture.

Leukocytes without nitrites may be linked to infection with bacteria that do not produce nitrites, inflammation, stones, or improper urine collection. Therefore with such a finding the test is often repeated with strict adherence to hygiene.

Crystals in the urine (urates, oxalates, phosphates) often depend on the diet, the concentration of the urine, and its pH. Isolated crystals without symptoms usually have no significance, but abundant crystalluria together with lower back pain may indicate urolithiasis.

Hyaline casts after exercise are a normal finding, whereas erythrocyte or granular casts in urine collected at rest indicate kidney damage and require a nephrologist consultation.

What to do with deviations: a practical plan

The first rule is not to draw conclusions from a single test taken after training. Most post-exercise changes disappear within 24–72 hours, so a repeat test after rest often clears everything up.

1. repeat the test after 48–72 hours without intense training;
2. collect the first morning midstream portion with adherence to hygiene;
3. hydrate well the day before, but do not drink excessively before collection;
4. inform the doctor about supplements, drugs, and menstruation;
5. with persistent changes — further workup: albumin/creatinine, blood creatinine and cystatin C, kidney ultrasound, urine culture.

You should see a doctor urgently with dark, tea- or cola-colored urine after exercise, severe muscle pain, noticeable blood in the urine, fever with lower back pain, and also with the appearance of glucose and ketones together with feeling unwell.

For prevention, a gradual increase in load, adequate hydration, careful use of nonsteroidal anti-inflammatory drugs, and avoiding the uncontrolled use of drugs that can damage the kidneys are important.

A regular urinalysis at rest is a good way to have your own “baseline” against which later results can be compared.

Editorial conclusions

Deviations in a urinalysis in athletes are often a temporary response to training or dehydration: protein, erythrocytes, and casts usually disappear after a few days of rest.

However, myoglobinuria, persistent proteinuria or hematuria at rest, glucose and ketones in the urine require a doctor's attention. The key to correct interpretation is a repeat test under standard conditions.

We also advise reviewing materials on what a urinalysis shows, on the glomerular filtration rate in athletes, and on rhabdomyolysis after training.

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