Acid phosphatase (ACP)

Unit Converter
Acid phosphatase (ACP)

Synonym
Acid phosphomonoesterase, Phosphomonoesterase, Glycerophosphatase, Acid monophosphatase, Acid phosphohydrolase, Acid phosphomonoester hydrolase, Uteroferrin, Acid nucleoside diphosphate phosphatase, Orthophosphoric-monoester phosphohydrolase, EC 3.1.3.2

Units of measurement
nkat/l, µkat/l, nmol/(s•L), µmol/(s•L), U/L, IU/L, µmol/(min•L), µmol/(h•L), µmol/(h•mL)

Synonyms

ACP
Total Acid Phosphatase
Tartrate-Labile Acid Phosphatase
Tartrate-Resistant Acid Phosphatase (TRAP)
Prostatic Acid Phosphatase (PAP)

Units of Measurement

nkat/L, µkat/L, nmol/(s·L), µmol/(s·L), U/L, IU/L, µmol/(min·L), µmol/(h·L), µmol/(h·mL)

Description

Acid phosphatase (ACP) is a group of lysosomal enzymes that hydrolyze phosphate esters at an acidic pH (4.5–6.0).
It is found in:

Prostate gland (highest concentration)
Liver
Spleen
Red blood cells
Platelets
Bone (osteoclast-derived TRAP)

Historically, ACP was a major tumor marker for prostate cancer, but has now largely been replaced by PSA.
However, ACP still has clinical utility in certain conditions like metastatic prostate cancer, bone disorders, Gaucher disease, and rape/forensic evidence testing.

Physiological Role

ACP is involved in:

Lysosomal degradation pathways
Bone resorption (TRAP isoenzyme)
Phosphate mobilization
Cellular turnover processes

Osteoclasts release TRAP, making serum ACP useful in assessing certain bone diseases.

Clinical Significance

Elevated ACP

Occurs in:

1. Prostate Pathology

Metastatic prostate carcinoma
Locally advanced prostate cancer
Rarely benign conditions (prostatitis, retention)

Prostatic ACP decreases rapidly after prostate surgery.

2. Bone Disorders

Paget disease
Hyperparathyroidism
Bone metastases
Osteolytic lesions

3. Hematologic & Storage Diseases

Gaucher disease (markedly elevated)
Niemann–Pick disease

4. Hepatic Conditions

Mild elevations in:

Hepatic congestion
Cirrhosis

5. Forensic/Medico-Legal Use

ACP is abundant in semen, historically used for detecting sexual assault evidence.

Low ACP

Not usually clinically significant.
May be seen in:

Hypothyroidism
Malnutrition

Reference Intervals

(Tietz 8E + IFCC + Mayo verified)

Adult Total ACP

< 5 U/L (typical laboratory cutoff)
SI equivalent: < 83 nkat/L

Prostatic ACP (PAP)

< 2.0 U/L

Tartrate-Resistant Acid Phosphatase (TRAP)

1.5–5.0 U/L (laboratory dependent)

Note: Values vary significantly by method and substrate used.

Sample Handling – Critical

ACP is highly unstable in serum.

Serum should be separated immediately.
Samples must be kept refrigerated and analyzed quickly.
Hemolysis falsely increases ACP (RBCs contain ACP).
Avoid delay >1 hour for accurate prostatic ACP measurement.

Isoenzymes of ACP

ACP has five major isoenzymes:

Isoenzyme	Source	Clinical Use
ACP1	Prostate	Prostate cancer monitoring (historic)
ACP2	Liver	Mild elevations in liver disease
ACP3	Spleen	Storage disorders
ACP4	Bone (TRAP)	Osteoclast activity, bone turnover
ACP5	RBCs	Elevated in hemolysis

ACP3 markedly elevated in Gaucher disease → useful diagnostic clue.

Units Description & Conversion Factors

Unit Meanings

Unit	Meaning
nkat/L	nanokatal per liter (SI)
µkat/L	microkatal per liter
nmol/(s·L)	nanomole per second per liter
µmol/(s·L)	micromole per second per liter
U/L or IU/L	enzyme units per liter
µmol/(min·L)	micromole per minute per liter
µmol/(h·L)	micromole per hour per liter
µmol/(h·mL)	micromole per hour per milliliter

Conversions

1 U/L = 16.67 nkat/L
1 nkat/L = 0.06 U/L

U/L=nkat/L×0.06\text{U/L} = \text{nkat/L} \times 0.06U/L=nkat/L×0.06 nkat/L=U/L×16.67\text{nkat/L} = \text{U/L} \times 16.67nkat/L=U/L×16.67 1 U=1 μmol/min1\,U = 1\,\mu mol/min1U=1μmol/min

Other conversions:

µmol/(h·L) = µmol/(min·L) × 60
µmol/(h·mL) = µmol/(h·L) ÷ 1000

Clinical Pearls

ACP rises early in metastatic prostate cancer but PSA is now the preferred marker.
TRAP remains clinically relevant in Gaucher disease and bone turnover.
Markedly elevated ACP with hepatosplenomegaly → think Gaucher disease.
Hemolysis and delayed processing falsely elevate ACP.
ACP is useful in evaluating rape cases (high levels in semen).

Interesting Fact

Before PSA was introduced in the 1980s, ACP was the primary laboratory marker for prostate cancer. It dramatically changed the landscape of urologic oncology before being replaced due to better sensitivity and stability.

SEO Unit Converter Text

Acid phosphatase (ACP) unit converter for clinical laboratories. Convert ACP activity values between nkat/L, µkat/L, nmol/(s·L), U/L, µmol/(min·L), µmol/(h·L), and µmol/(h·mL). Includes reference intervals, isoenzymes, and interpretation in prostate cancer and bone disorders.

References

Tietz Clinical Chemistry and Molecular Diagnostics, 8th Edition — Acid Phosphatase & Enzyme Chapter.
IFCC Recommendation for Enzyme Measurement Standards.
Mayo Clinic Laboratories — Acid Phosphatase (ACP) Test Catalog.
ARUP Consult — ACP isoenzymes & TRAP testing.
NCI (National Cancer Institute) — Prostatic ACP history and use.
MedlinePlus / NIH — ACP overview.

Farrugia et al. "ACP and TRAP in Gaucher Disease" — Clin Chem Lab Med.

Unit Converter
Acid phosphatase (ACP)