Citrate 24 Hour Test

If you have ever passed a kidney stone or worry about forming one, urinary citrate is one of the most useful numbers you can know. Citrate (citric acid salt) is your body's built-in defense against calcium stones. It works by grabbing onto calcium in your urine and keeping it dissolved, preventing the calcium from clumping into crystals that eventually become stones. A 24-hour urine collection measures how much citrate your kidneys are excreting, and a low result, called hypocitraturia, means that defense system is underperforming.

The standard threshold is 320 mg per day: anything below that is considered low. Among people who form kidney stones repeatedly, about 32.2% have hypocitraturia, compared to only 14.3% of people who do not form stones. That makes low citrate one of the most common correctable metabolic problems behind calcium kidney stones.

The test is straightforward. You collect all your urine over 24 hours, and the lab reports total citrate excretion. The number itself tells you how much protective citrate your kidneys are putting out. But interpreting it well means understanding what drives that number up or down, and what you can do about it.

Why Your Body Sometimes Runs Low on Citrate

The single biggest factor controlling urinary citrate is your body's acid-base balance. When your blood becomes even slightly more acidic, your kidneys respond by pulling citrate back out of the urine and using it as a chemical buffer. The result: less citrate reaches your bladder, and your stone risk goes up. Anything that shifts your body toward a more acidic state, whether it is diet, medication, or an underlying condition, can lower your citrate.

This is why kidney function matters so much when reading your result. In people with chronic kidney disease, the body often accumulates acid silently, and urinary citrate drops as a consequence. In fact, the ratio of citrate to creatinine in a spot urine sample may be a better indicator of hidden acid buildup than standard blood tests, because it reflects the kidney's active effort to compensate rather than the blood level that is being defended.

Several everyday factors also play a role. Diets high in nondairy animal protein push the body toward acidity and are linked to lower citrate (roughly 20 mg/day less for every additional 10 grams of animal protein per day). Higher body weight is associated with modestly lower citrate (about 4 mg/day less per 1 kg/m² increase in BMI). Having high blood pressure is linked to about 95 mg/day less citrate, and gout is associated with about 104 mg/day less. Low vegetable fiber intake and low fluid intake are additional risk factors.

On the flip side, eating more potassium-rich foods is associated with higher citrate excretion (roughly 53 mg/day more per 1,000 mg of dietary potassium). If you are a stone former with low citrate, increasing your intake of fruits and vegetables is one of the simplest places to start.

The Calcium-to-Citrate Ratio: A Sharper View of Risk

Your citrate level alone is informative, but comparing it to how much calcium is in your urine gives an even clearer picture. The urinary calcium-to-citrate ratio captures the balance between the stone-promoting force (calcium) and the stone-blocking force (citrate) in a single number.

If your kidney function is normal, a ratio above 0.25 may signal intense stone-forming activity. In one study of stone formers versus non-stone formers, this cutoff identified severe stone risk with 89% sensitivity and 57% specificity. That means the ratio caught about 89 out of 100 people with the most active stone disease. A high ratio was also linked to lower bone mineral density and increased markers of bone breakdown, suggesting that the same metabolic imbalance driving stones may also be weakening bone.

This ratio is highest in early morning urine, which helps explain why overnight and early morning hours represent a peak window for stone crystal formation. If you are collecting a spot urine sample rather than a full 24-hour collection, the timing of the sample matters.

What Moves This Biomarker

Urinary citrate is responsive to both lifestyle changes and medications. Here is what the evidence shows about the most impactful levers.

Diet and lifestyle: Increasing potassium intake from fruits, vegetables, and other whole foods is associated with higher citrate excretion in observational studies. Getting more vegetable fiber and drinking enough fluid to maintain adequate urine volume are also linked to better citrate levels. Reducing nondairy animal protein may help by lowering your body's acid load.

Potassium citrate supplementation: This is the primary medical treatment for low citrate. At a dose of 60 mEq per day, potassium citrate raises urinary citrate by approximately 400 mg/day and increases urinary pH by about 0.7 units. The effect begins within the first hour of dosing and reaches its peak by the third day with regular use. Higher doses (60 mEq/day) are recommended for severe hypocitraturia (citrate below 150 mg/day), with lower doses for milder cases. Potassium citrate is preferred over sodium citrate because the sodium form can increase urinary calcium, partially undermining the benefit. This data comes from prescribing information for the medication.

Combination therapy: Combining a thiazide diuretic with potassium citrate may be more effective than either alone, because thiazides lower urinary calcium by roughly 50% while the citrate supplement restores the citrate that thiazides modestly reduce. This is supported by American Urological Association guidelines.

Some people, however, do not respond to potassium citrate as expected. This phenomenon, sometimes called citrate resistance, means that despite receiving adequate potassium, urinary citrate does not rise sufficiently. If you supplement and retest without meaningful improvement, that is important information to share with your clinician.

Several common medications can lower your citrate and are worth knowing about if you are monitoring stone risk:

Sources: Welch et al.; Pelzman et al.; Seitz and Jaworski; Mandel et al.; Melnick et al.

What this means for you: if you are taking any of these medications and have a history of kidney stones, testing your urinary citrate gives you a concrete way to assess whether the drug is shifting your stone risk. Topiramate deserves special attention because its effect is large, but the good news is that citrate levels recover after stopping the drug, with one study showing an increase from 225 mg/day to 614 mg/day after cessation. Combining topiramate with other acid-producing medications or a ketogenic diet further increases stone risk and should be avoided.

How to Read Your Result

Because acid-base status, kidney function, and medications all strongly influence citrate excretion, always consider these factors before interpreting a number in isolation. Certain lab methods can occasionally affect the result, so confirm with your lab if a value seems inconsistent with your clinical picture.

If your level is below 320 mg/day, it means your urine lacks enough of this natural stone inhibitor. This is especially relevant if you also have elevated urinary calcium, because the combination amplifies risk far more than either abnormality alone. A calcium-to-citrate ratio above 0.25 is an additional red flag worth discussing with your clinician.

If you have chronic kidney disease, your citrate may be low even without any other classic stone risk factors. In this setting, a spot urine citrate-to-creatinine ratio can be a useful marker of acid retention that blood tests may miss.

Questions This Biomarker Can Answer

• Is my body producing enough of its natural defense against calcium kidney stones?
• Could a medication I take be lowering my stone protection without my knowing?
• Is my diet shifting my body's acid-base balance in a way that increases stone risk?
• Is the balance between calcium and citrate in my urine putting me in a high-risk zone for stone formation?
• If I have chronic kidney disease, is my body silently accumulating acid even though my blood tests look normal?