Lysine - Quantitative Urine 24 Hr Test

The Lysine - Quantitative Urine 24 Hr test is a specialized metabolic investigation that measures the total amount of lysine excreted in all urine produced during a complete 24-hour period. The test may be used to investigate inherited amino-acid transport disorders, renal aminoaciduria, lysinuric protein intolerance, cystinuria, and selected abnormalities involving lysine metabolism or kidney tubular function.

Lysine is an essential amino acid, meaning that the body cannot produce enough of it and must obtain it from dietary protein. Lysine is required for normal growth, protein synthesis, tissue repair, enzyme and hormone production, immune function, and the formation of carnitine and collagen-related structures.

After dietary proteins are digested, amino acids are absorbed through the intestine and enter the bloodstream. The kidneys filter amino acids and normally reabsorb most of them through specialised transport systems in the renal tubules. Only limited quantities are ordinarily lost in urine. Increased urinary lysine may occur when an inherited transport defect prevents normal kidney reabsorption or when generalised tubular dysfunction causes multiple amino acids to spill into urine.

A 24-hour collection measures total lysine excretion throughout an entire day. This can provide a more integrated assessment than a single random urine specimen, although urinary amino-acid excretion is still influenced by age, diet, protein intake, kidney function, medicines, illness, and collection completeness.

The result cannot independently diagnose a specific inherited disorder. It should be interpreted with quantitative plasma amino acids, other urinary amino acids, urine cystine, kidney function, clinical symptoms, family history, newborn-screening information, and molecular genetic testing when appropriate.

Benefits of the Lysine Quantitative Urine Test

• Measures total lysine excretion over a complete 24-hour collection period.
• Supports the evaluation of suspected lysinuria or abnormal renal lysine transport.
• May contribute to the assessment of lysinuric protein intolerance.
• Can form part of the biochemical evaluation of cystinuria.
• Helps assess disorders involving cationic amino acids such as lysine, arginine, and ornithine.
• May provide evidence of kidney tubular amino-acid loss.
• Can be interpreted with plasma amino acids and genetic testing.
• May assist monitoring in patients with an established metabolic or transport disorder.
• Provides quantitative information rather than only indicating whether lysine is present.
• Supports specialist evaluation by a metabolic physician, nephrologist, geneticist, or paediatrician.

Clinical Indications and Applications

Lysinuric Protein Intolerance: Lysinuric protein intolerance is a rare inherited disorder caused by impaired transport of cationic amino acids, particularly lysine, arginine, and ornithine, in the intestine and kidneys. It is associated with pathogenic variants in the SLC7A7 gene.

Affected individuals may have high urinary excretion of cationic amino acids, especially lysine, while plasma lysine, arginine, and ornithine may be low or occasionally within their reference intervals. Symptoms can include poor tolerance of protein-rich food, vomiting after protein intake, poor growth, enlarged liver and spleen, muscle weakness, osteoporosis, blood-cell abnormalities, lung involvement, and episodes of high blood ammonia.

Cystinuria: Cystinuria is an inherited disorder affecting the renal transport of cystine and the dibasic amino acids lysine, ornithine, and arginine. Increased urinary cystine can form recurrent kidney stones because cystine is relatively insoluble. Lysine itself generally does not form stones, but its increased urinary excretion can support the biochemical pattern of the transport defect.

A complete cystinuria assessment generally includes quantitative cystine, lysine, ornithine, and arginine rather than lysine alone. Stone analysis, urinary pH, imaging, family history, and genetic testing may also be required.

Renal Tubular Dysfunction: Generalised proximal tubular dysfunction can cause multiple amino acids and other filtered substances to be lost in urine. Urinary amino-acid testing may contribute to the assessment of Fanconi syndrome, selected inherited kidney disorders, mitochondrial disease, medication-related tubular injury, or other acquired renal conditions.

Other Aminoacidurias: Abnormal urinary lysine may appear with broader patterns of aminoaciduria. The significance depends on whether lysine alone, cationic amino acids, or many unrelated amino acids are elevated.

Abnormal Newborn or Metabolic Screening: Quantitative urine amino-acid measurement may be used as a follow-up investigation after an abnormal newborn-screening result or when a child has unexplained developmental, neurological, nutritional, liver, renal, or metabolic findings.

Monitoring a Confirmed Disorder: A metabolic specialist may use serial urinary lysine measurements with plasma amino acids, ammonia, growth assessment, nutrition review, and organ-function testing to monitor selected patients.

Why Doctors Recommend This Test

Doctors recommend this test when symptoms, family history, kidney stones, biochemical abnormalities, or screening results suggest an amino-acid transport or metabolic disorder. Measuring urinary lysine can help determine whether an excessive amount is being lost through the kidneys.

The pattern of accompanying amino acids is often more informative than lysine alone. In lysinuric protein intolerance, urinary lysine is typically increased with arginine and ornithine. In cystinuria, cystine, lysine, ornithine, and arginine may all be elevated. Generalised tubular dysfunction may cause a broader range of amino acids to increase.

A 24-hour measurement may help calculate total daily excretion and, in selected cases, renal lysine clearance. Renal clearance calculations may require simultaneous fasting plasma lysine, total urine volume, collection duration, and other laboratory values.

Quantitative urine lysine is not a general nutrition test and does not directly measure whether dietary protein intake is adequate. A high urine result can coexist with low plasma lysine when a transport defect causes excessive renal loss.

Preparation Before the Test

Follow the collection instructions supplied by Focus Diagnostics. The laboratory will provide an approved 24-hour urine container and explain whether a preservative is required. Do not discard the preservative, rinse the container, or add acid or another substance yourself.

The referring doctor may advise continuing a normal diet so the collection reflects usual amino-acid intake. In other situations, a controlled diet or timed fasting plasma sample may be required. Follow the metabolic specialist's instructions exactly.

Inform the doctor about prescription medicines, non-prescription medicines, amino-acid supplements, protein powders, nutritional formulas, vitamins, herbal products, and specialised metabolic diets. Do not stop treatment or alter a prescribed diet without medical advice.

Provide the patient's age, height, weight, clinical symptoms, family history, dietary information, medicines, and suspected diagnosis. Age is particularly important because amino-acid excretion and reference intervals differ between infants, children, adolescents, and adults.

Tell the laboratory about kidney disease, liver disease, recent illness, fever, burns, malnutrition, pregnancy, parenteral nutrition, or recent major dietary changes. These factors may affect amino-acid results.

Plan the collection on a day when every urine specimen can be collected. Ask whether the container must be refrigerated, frozen, protected from light, or kept in another controlled condition. Follow the supplied storage instructions.

How Is the 24-Hour Urine Sample Collected?

Select a convenient starting time, commonly after waking in the morning. At that time, empty the bladder into the toilet and do not add this first specimen to the container. Record the exact starting date and time.

After discarding the first specimen, collect every urine sample produced during the following 24 hours. This includes urine passed during the day, overnight, and during bowel movements. Use a clean collection aid if supplied by the laboratory.

At the same time on the following morning, collect the final urine specimen and add it to the container. For example, if the first urine was discarded at 7:00 AM on the first day, include the urine passed at approximately 7:00 AM on the next day.

Keep the container securely closed and store it exactly as directed. Prevent contamination with stool, toilet paper, menstrual blood, tap water, soap, powder, disinfectant, or cleaning products.

If any urine is missed, spilled, or discarded accidentally, contact the laboratory. The collection may need to be restarted because missing one specimen can produce a falsely low total lysine result. Do not extend the collection to compensate unless instructed.

Return the complete specimen promptly with the start time, finish time, and required patient information. The laboratory records the total urine volume, mixes the specimen, and analyses an aliquot using an appropriate quantitative amino-acid method, such as liquid chromatography with tandem mass spectrometry or another validated technique.

Normal Reporting Time

The report for the Lysine - Quantitative Urine 24 Hr test is generally available within 7 to 10 working days. This is a specialised metabolic investigation that may require batch processing or analysis at a referral laboratory.

The turnaround time may vary because of sample transport, preparation, quality-control requirements, repeat analysis, confirmation of abnormal values, or specialist interpretive review. Patients should confirm the expected reporting time with Focus Diagnostics.

Who Should Consider This Test?

• Patients with suspected lysinuric protein intolerance.
• Individuals undergoing biochemical evaluation for cystinuria.
• Patients with recurrent cystine kidney stones or a family history of cystinuria.
• Children with poor growth, protein intolerance, or unexplained metabolic symptoms.
• Patients with unexplained high ammonia after protein intake.
• Individuals with suspected renal tubular dysfunction or aminoaciduria.
• Patients with an abnormal plasma amino-acid or newborn-screening result.
• Individuals with a known amino-acid transport disorder requiring monitoring.
• Patients referred by a metabolic specialist, nephrologist, geneticist, or paediatrician.
• Individuals able to complete an accurate 24-hour urine collection.

Understanding the Test Results

The result may be reported as the total amount of lysine excreted during 24 hours, a concentration, or another method-specific unit. Interpretation depends on age, total urine volume, dietary protein, kidney function, other amino-acid results, and collection completeness.

Elevated Urinary Lysine: Increased lysine excretion may occur in lysinuric protein intolerance, cystinuria, renal tubular transport disorders, generalised aminoaciduria, and selected acquired conditions. The result does not identify the specific cause by itself.

Marked urinary lysine with increased arginine and ornithine and low or normal plasma cationic amino acids may support lysinuric protein intolerance. Genetic testing for biallelic pathogenic variants in SLC7A7 can confirm the diagnosis when clinical and biochemical findings are compatible.

Elevated lysine with cystine, ornithine, and arginine may support cystinuria. Cystine measurement is central because cystine causes stone formation. Genetic testing involving the relevant transport genes may be considered.

Result Within the Reference Interval: A result within the laboratory's expected range means that increased 24-hour lysine excretion was not detected during that collection. It does not completely exclude an intermittent, mild, age-dependent, diet-related, or clinically complex transport disorder.

Low Urinary Lysine: Low excretion may reflect reduced dietary protein, low plasma lysine, incomplete collection, or another nutritional or metabolic factor. It cannot independently diagnose lysine deficiency.

The doctor may request quantitative plasma amino acids, a full urine amino-acid profile, urinary cystine, ammonia, liver and kidney function tests, urine creatinine, genetic testing, imaging, and nutritional assessment.

Clinical Limitations

Incomplete urine collection is a major limitation. Missing urine can falsely lower the calculated excretion, while collecting beyond 24 hours may falsely increase it. Incorrect total volume or timing also affects accuracy.

Diet, protein intake, supplements, medicines, age, illness, kidney function, liver function, and sample storage can influence amino-acid results. A single measurement may not represent the long-term biochemical pattern.

Lysine alone cannot differentiate cystinuria from lysinuric protein intolerance or generalised renal aminoaciduria. The pattern of plasma and urinary amino acids is essential.

Reference intervals differ substantially by age, analytical method, unit, and collection type. The laboratory's report should be used instead of unrelated reference ranges.

Important Safety Information

Seek urgent medical care for confusion, unusual sleepiness, persistent vomiting, breathing difficulty, seizures, sudden neurological changes, or suspected high ammonia. Acute metabolic decompensation can require emergency treatment.

Do not increase or restrict protein, lysine, arginine, or other amino acids based only on this result. Inherited metabolic disorders require individualized dietary and medical management.

Patients with suspected cystinuria should not begin or stop stone-prevention medicines without consulting a nephrologist or urologist. Hydration, urinary alkalinisation, diet, and medicines require personalised supervision.

This information is intended for general education and does not replace diagnosis or advice from a metabolic specialist, geneticist, nephrologist, paediatrician, or dietitian.