The present field based study showed that the PIMA analyzer gave comparable results with the reference methodologies for different CD4 ranges; one of the important characteristics for the validation of a new technology. The study could analyze more than 300 samples (range 369 to 508) samples at each CD4 range; <250, 251–350, 351–500 and >500 cells/mm3 and the analysis showed very low relative bias within the PIMA and reference methodologies. Before distribution of the machines to various centers the inter machine comparison showed less than 10 percent%CV for both high and low CD4 counts for either the stabilized blood samples or fresh blood samples indicating good precision. The onsite inter-instrument variation was also within the 10% limit indicating the efficient use of PIMA analyzer as POC machine. The sensitivity and specificity of the PIMA analyzer to identify the patients with CD4 count less than 350, was found to be 91%. This indicated that the use of PIMA would put additional burden on the treatment providers as the treatment would be given to the patients who still have CD4 counts above 350. However the analysis showed that more than 50% mismatched results were between CD4 counts of 320 to 380; indicating that most of the patients would need ART in short time. The previously reported study has showed higher sensitivity but lower specificity to identify patients with CD4 counts lower than 350 cells (8). Previous studies have also shown less precision for the finger prick samples and also indicated that the finger prick sample collection required adequate training for correct use of the samples (7,8,12). Our study confirmed that the finger prick samples could be tested on PIMA analyzer with slightly less efficiency and also confirmed the requirement of the operator training for proper collection of finger prick sample to avoid multiple pricks. It was observed that in case of insufficient and improper finger-prick sample collection, the reliability of the CD4 counts by PIMA analyzer was questionable. Also our study participants preferred to give venous blood sample. The primary reasons were requirement of blood collection for other investigations using venous blood and a fear of being subjected to multiple pricks if sufficient volume of blood is not obtained in a single prick. Hence the finger prick blood sample could be the method of choice when only CD4 testing has to be carried out. The PIMA CD4 analyzer is battery operated and the reagents are stable at room temperature making it suitable for use in the areas where the reliable electric supply is not available and the ambient temperatures are often high. The cartridges have shelf life of six months making it suitable for remote areas where the shipment, delivery and storage, would be difficult. The testing does not require any additional equipment. The analyzer can be used after a minimum training and can be run by the clinical staff such as nurses where multi-tasking may be necessary due to shortage of trained staff or lack of sufficient workload .
The stabilized blood samples could be tested reliably by PIMA analyzer indicating amenability of the system for participation in the External Quality Assurance Scheme.
Unlike other CD4 enumerating equipments, in PIMA analyzer, the complete process of staining takes place in the equipment itself. Hence the sample throughput would be relatively low and the analyzer would be useful at the centres with 10–20 patients load/day. However, it is not expected that peripheral centres will have higher patient load and more than one machine could be installed in the centres if required.
The countrywide national ART roll out programme in India comprises of 300 ART centers and 550 linked centers with 3,64,000 adult populations on ART by January 2011 . The availability of CD4 counts in selected centers required either long distance travel for the patient or transport of the sample to the laboratory. This resulted in missed visits of the patients and problems in patient management. The loss to follow up of HIV infected patients after the diagnosis has been reported to be in the range of 16 to 25% in India , personal communication]. Although multiple factors are responsible for loss to follow up, availability of CD4 testing at point of care will help in reducing the number of clinic visits, thus helping in reducing loss to follow up. A recent report from Africa showed that POC CD4 testing could successfully reduce the pretreatment loss to follow-up . Also the implementation of 350 CD4 count as a cut off for ART initiation instead of earlier cutoff of 250 would increase the burden on CD4 testing facility. Hence the decentralization of CD4 testing by providing CD4 count at primary health centers in combination with HIV diagnosis could enable proper monitoring of disease progression and ART initiation at the primary health centers only and would maximize the public health benefit of POC technology.
The PIMA analyzer does not provide percentage of CD4+ cells; hence, it would not be useful for monitoring the paediatric population younger than 5 years. As the movement of the paediatric patients/samples is difficult in the periphery, unavailability of CD4 percentage at the peripheral centre could be one of the limitations of this POC machine. In such cases the dual platform technology can be used by using absolute lymphocyte counts from hematology analyzer or from peripheral blood smear and the absolute CD4 counts from PIMA analyzer to calculate CD4 percentages. However the disadvantages would be of influence of the variation due to another system.
The cost of the PIMA analyzer is lesser than the available single platform CD4 machines and the cost of the cartridge is around 10 US$ which is slightly higher which might pose problem if not procured in bulk amount where the cost benefit could be obtained.
In conclusion, the study showed that the POC PIMA CD4 analyzer would be suitable for use in remote areas with minimum or no infrastructure. The availability of the CD4 counts on the same day of sample collection would reduce the number of repeat visits and improve patient management. Hence the integration of POC CD4 testing into the national AIDS control program would facilitate the better patient management in HIV infection.