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Titratable Acid Capacity of Serum (TAC) – Measured as a qualitative probe for serum

Published: August 9, 2026Updated: August 16, 2026

This test evaluates how much acid a sample of your blood can neutralize, which helps assess kidney function and acid-base balance.

Quick summary

["A simple blood test to check kidney ability to regulate acid levels in your body."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
26009-1
Short code
T palldm Ab Titr Ser HA
Synonyms
T palldm Ab Titr Ser HA
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ha
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What This Test Measures

Titratable acid capacity (TAC) reflects the amount of weak acids in your serum that can react with a base (like sodium hydroxide) during titration. It indirectly measures how well your kidneys filter and excrete hydrogen ions, which is critical for maintaining your body’s acid-base balance.

Why It’s Done

Your healthcare provider may order this test if you have symptoms like fatigue, muscle weakness, or signs of kidney disease. It can also be part of broader metabolic evaluations, especially in patients with chronic kidney conditions or acid-base disorders.

When to Expect Results

Results are qualitative (yes/no or present/absent) rather than numeric, so you’ll receive a clear pass/fail or qualitative indication rather than a specific value.

What to Expect Before the Test

No special preparation is typically needed. You may fast for 8–12 hours before the blood draw if instructed, but this test does not require fasting.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Low TAC levels may indicate impaired kidney function, metabolic acidosis, or other conditions affecting acid excretion. High levels could suggest overcompensation from conditions like diabetes or severe dehydration. This test is less commonly used than direct pH or bicarbonate measurements but can be valuable in specific clinical scenarios.

Short name

TAC (Serum)

Frequently asked questions

What does a low TAC mean?
A low TAC suggests your kidneys may struggle to remove excess acid from your blood, which could signal kidney dysfunction or metabolic acidosis. Your doctor will discuss further testing or treatment options based on your overall health.
How is this test different from a pH test?
Unlike a pH test, which measures the direct acidity of your blood, TAC assesses the *capacity* of your serum to neutralize acid. It’s a complementary measure often used alongside other acid-base indicators like bicarbonate levels.
Can diet affect this test?
Dietary factors like high protein intake (which increases acid load) or certain medications (e.g., diuretics) may influence acid metabolism, but this test itself doesn’t require strict dietary restrictions. Your provider will consider your overall health context.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy