The value of percentage free prostate specific antigen (PSA) in the detection of prostate cancer among patients with intermediate levels of total PSA (4.0–10.0 ng/mL) in Nigeria

Figures & data

Table 1 The values of PSA and its derivatives.

Variable	Mean (SD, range)
tPSA (ng/mL)	6.6 (1.7, 4.1–9.9)
fPSA (ng/mL)	2.9 (1.3, 0.7–6.0)
%fPSA	0.48 (0.16, 10–80)

Table 2 The %fPSA and histological diagnosis.

%fPSA	Prostate cancer	BPH	Total
⩽10	1	0	1
11–20	8	1	9
21–30	4	2	6
31–40	1	3	4
41–50	0	44	44
51–60	0	20	20
61–70	0	13	13
71–80	0	8	7
Total	14	91	105

Figure 1 The ROC curve showing the sensitivity (true-positive rate) against (1 – specificity) (false-positive rate) for %fPSA levels. The AUC was 0.99, and P < 0.001.

Figure 2 A decision plot showings the sensitivity (true-positive rate) and specificity (true-negative rate) curves of %fPSA levels. The point where the lines cross is the optimum threshold level. From the plot the decision level for %fPSA that optimally identified all the patients with cancer of the prostate (true positive) or nodular hyperplasia (true negatives) was <40%.

Table 3 The sensitivity, specificity and PPVs at various thresholds of %fPSA.

%fPSA threshold	Sensitivity (%)	Specificity (%)	PPV (%)
<40	100	93.4	70.0
<35	92.9	95.5	72.2
<30	85.7	96.7	80.0
<25	78.6	97.8	84.6
<20	57.1	98.9	88.9
<15	35.7	100	100
<10	7.14	100	100

Table 4 Gleason scores and %fPSA values of the 14 patients with prostate cancer.

Patient	Gleason score	%fPSA
1	2	38
2	3	28
3	3	21
4	5	16
5	5	17
6	6	21
7	6	22
8	6	22
9	6	15
10	6	14
11	7	14
12	7	16
13	7	12
14	9	10

Table 5 The variation in the optimum %fPSA based on race.

Study	Country (race) population size	Target tPSA range (ng/mL)	Optimum %fPSA threshold	Sensitivity (%)
Present	Nigerians (Black), 105	4.1–9.9	<40	100
[6]	Americans (Black), 79	4.1–9.9	<25	95
	(white), 647	4.1–9.9	<25	95
[21]	Americans (Black), 222	2.5–9.9	<35.2	95
	(white), 298	2.5–9.9	<29.2	95
[18]	Japanese, 301	4.1–9.9	<15.5	85
[17]	Japanese, 97	4.1–9.9	<17	91

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