Performance of serum C-reactive protein as a screening test for smear-negative tuberculosis in an ambulatory high HIV prevalence population.
BACKGROUND
Delayed diagnosis has contributed to the high mortality of sputum smear-negative tuberculosis (SNTB) in high HIV prevalence countries. New diagnostic strategies for SNTB are urgently needed. C-reactive protein (CRP) is a non-specific inflammatory protein that is usually elevated in patients with tuberculosis, but its role in the diagnosis of tuberculosis is uncertain.


RESULTS
To determine the diagnostic utility of CRP we prospectively evaluated the performance of CRP as a screening test for SNTB in symptomatic ambulatory tuberculosis suspects followed up for 8 weeks in KwaZulu-Natal, South Africa. Confirmed tuberculosis was defined as positive culture or acid-fast bacilli with granulomata on histology, and possible tuberculosis as documented response to antitubercular therapy. The CRP quotient was defined as a multiple of the upper limit of normal of the serum CRP result. Three hundred and sixty four participants fulfilled entry criteria: 135 (37%) with confirmed tuberculosis, 114 (39%) with possible tuberculosis, and 115 (24%) without tuberculosis. The median CRP quotient was 15.4 (IQR 7.2; 23.3) in the confirmed tuberculosis group, 5.8 (IQR 1.4; 16.0) in the group with possible tuberculosis, and 0.7 (IQR 0.2; 2.2) in the group without tuberculosis (p<0.0001). The CRP quotient above the upper limit of normal had sensitivity 0.98 (95% CI 0.94; 0.99), specificity 0.59 (95% CI 0.50; 0.68), positive predictive value 0.74 (95% CI 0.67; 0.80), negative predictive value 0.96 (95% CI 0.88; 0.99), and diagnostic odds ratio 63.7 (95% CI 19.1; 212.0) in the confirmed tuberculosis group compared with the group without tuberculosis. Higher CRP quotients improved specificity at the expense of sensitivity.


CONCLUSIONS
In high HIV prevalence settings a normal CRP could be a useful test in combination with clinical evaluation to rule out tuberculosis in ambulatory patients. Point-of-care CRP should be further evaluated in primary care clinics.
Department of Medicine, Edendale Hospital, Pietermaritzburg, University of KwaZulu-Natal, KwaZulu-Natal, South Africa. wilsondpk@gmail.com
Douglas
D
Wilson
Motasim
M
Badri
Gary
G
Maartens
D017088:AIDS-Related Opportunistic Infections / Q000175:diagnosis*; D000328:Adult; D002097:C-Reactive Protein / Q000032:analysis*; D005260:Female; D015658:HIV Infections / Q000150:complications* / Q000453:epidemiology; D006801:Humans; D008297:Male; D008403:Mass Screening / Q000379:methods / Q000592:standards*; D019095:Point-of-Care Systems; D011237:Predictive Value of Tests; D015995:Prevalence; D012680:Sensitivity and Specificity; D013019:South Africa; D014376:Tuberculosis / Q000150:complications / Q000175:diagnosis*
D002097:C-Reactive Protein
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